Reactive N in Agric Environ Industry in India

ABOUT THE BOOK

ABOUT THE AUTHORS

• Bijay Singh • Mithilesh K. Tiwari • Yash P. Abrol

INDIAN NATIONAL SCIENCE ACADEMYBahadur Shah Zafar Marg, New Delhi-110002

Professor Bijay Singh, ICARNational Professor, has been workingon different aspects of nitrogen inrice-wheat cropping system for morethan two decades. His contributionson nitrogen balance in soil-plantsystems have lead to betterunderstanding for (i) enhancingnitrogen use efficiency in rice-wheatcropping system (ii) fertilizer nitrogenrelated environmental pollution, and(iii) integrated nutrient management.He is a fellow of Indian NationalScience Academy, National Academyof Agricultural Sciences and IndianSociety of Soil Science. He is decoratedwith several awards notably the RafiAhmad Kidwai Memorial Prize ofICAR. He is continuing work onincreasing fertilizer nitrogen useefficiency in rice and wheat at PunjabAgricultural University, Ludhiana.

Dr. Mithilesh K. Tiwari is Director ofthe South Asian Regional Centre of theInternational START Programme that isresponsible for nurturing regionalcooperation for studies on GlobalChange with particular emphasis nowon Climate Change Adaptation. Heheads the Centre on Global ChangeProject of CSIR and the Radio andAtmospheric Sciences Division,National Physical Laboratory at NewDelhi. He is an active Core TeamMember of the Indian Nitrogen Group.He has extensively contributed to thegrowth of several major national levelresearch programmes in space sciences.His research interests are atmosphericenvironmental change processes andimpacts. Currently member of INSA’sNational Committee for SCAR, he alsoserved the National Committees for IGBPand COSPAR.

Professor Yash P Abrol, formerly Headof the Division of Plant Physiology atthe Indian Agricultural ResearchInstitute, New Delhi, subsequent toserving as CSIR Emeritus Scientist andINSA Senior Scientist (1996-2001; 2001-2005), is at present associated with theDepartment of Environmental Botany,Hamdard University, New Delhi asAdjunct Professor and INSA HonoraryScientist,. He has immensely contributedto nitrogen research and has publishedprofusely in reputed journals. He isactively involved in organizing INDIAN

NITROGEN GROUP under the aegis ofthe Society for Conservation of Nature.He is a Fellow of the INSA, IndianAcademy of Sciences, National Academyof Sciences and NAAS. He receivedseveral awards notably ICAR NationalFellowship, FAI Dhirubhai MorarjiMemorial, R.D. Asana, Sukumar Basu,VASVIK and FICCI awards.

In Agriculture, Industry and Environment in India

Precipitation

Gaseous Losses

Nitrates Ammonium

Nitrites

Organic Residues

Organic Matter

Clay Minerals

Plant ConsumptionDenitrification

Leaching

Nitrificationthrough bacteria

Fixation

Mineralization

Jammu &Kashmir

HimachalPradesh

Uttaranchal

Rajasthan UttarPradesh

Sikkim

Bihar

WestBengal

TripuraMizoram

Manipur

NagalandMegalaya

Assam

ArunachalPradesh

Orissa

JharkhandMadhya PradeshGujarat

Mumbai(Bombay)

Maharashtra

AndhraPradesh

Goa

Lakshdeep

Karnataka

KeralaTamilNadu

Chennai (Madras)

Andaman & Nicobar

Kolkata(Calcutta)Chha

ttisgar

h

DELHI

Punjab

Atmospheric N2

WetlandVegetation

Denitrificationby denitrifyingbacteria

AssimilationNitrification bynitrifying bacteria Nitrites

(NO2)

Nitrogen(NO2)

Ammonium (NH4+)(NH4

+)

Nitrification bynitrifying bacteria

Open Water

Oceans containing CO(NH2)2

Seagull

Decayingdead animal

Nitrogen fixing soil bacteria

Decomposition(Bacteria andfungi)

Ammonification

The current status of reactive nitrogen which consists of all biologically, chemically and radiatively active nitrogencompounds in terrestrial, coastal and atmospheric realms and development of technologies to minimize nitrogenimpacts on the environment needs to be addressed in the right perspective. The development of policy to controlunwanted reactive N release in the environment is difficult because much of the reactive N release is relatedto food and energy production and reactive N species can be transported great distances in the atmosphereand in aquatic systems.

This publication is an outcome of the activities of the Indian Nitrogen Group, a national network of scientistsconcerned with issues related to reactive nitrogen. It presents an overview of reactive nitrogen in agriculture,industry and environment in India. Since reliable quantitative information about several aspects of reactivenitrogen in the country is not yet available, it should prove very valuable for the scientific community in termsof initiating projects to fill the gaps. It should also help planners in agriculture, industry and energy productionto guide future expansion in the economy in a way that the delicate balance between inputs and outputs ofreactive nitrogen in the environment is maintained.

Reactive Nitrogen in Agriculture,Industry and Environment in India

Bijay SinghM.K. Tiwari

andY.P. Abrol


i

© Indian National Science AcademyBahadur Shah Zafar Marg, New Delhi-110002

EPABX Nos.: 23221931-23221950 (20 lines)Fax : 91-11-23231095, 23235648E-mail : [email protected]; [email protected] : http://www.insaindia.org

Published by Shri SK Sahni, Executive Secretary on behalf of Indian National Science Academy, Bahadur Shah Zafar marg, New Delhi-110002and printed at Aakriti Graphics, New Delhi.

Foreword

The Indian National Science Academy (INSA), New Delhi, is the adhering body in India to the InternationalCouncil for Science (ICSU) and its affiliated International Unions / Committees / Commissions, etc. Ajoint National Committee of IGBP-WCRP-SCOPE, formed by INSA, looks after and supports the activitiesand implementation of various projects in these areas. The Committee decided that a series of statusreports be prepared on specific topics by leading Indian experts so that Indian work be highlighted atvarious general awareness be created among scientists and science students.

Recent assessments of the state of the environment across India indicate that the country’s risingeconomic prosperity is also putting the environment under stress. Human food and energy productionhas dramatically increased the amount of atmospheric N2 that is converted into reactive forms. As aconsequence there is a wide variety of beneficial and detrimental effects. Reactive nitrogen is thus associatedwith both growing economy in terms of food production and industry, and environmental degradation.Burgeoning human population depends upon food production made possible by synthetic nitrogenfertilizers. Combustion of fossil fuels adds more reactive nitrogen to air, water and soil. This distortionof the nitrogen cycle, while raising agricultural yields, causes degradation of water and air quality,biodiversity, ecosystem services and human health. Meanwhile, reactive nitrogen deficiencies on farmlandin many regions of the country continue to create economic and health hardships, and accelerate landdegradation. The development of policy to control unwanted reactive N release in the environment isdifficult because much of the reactive N release is related to food and energy production and reactiveN species can be transported great distances in the atmosphere and in aquatic systems. Although thenitrogen cycle provides a framework for assessing broad scale or even global strategies to improve nitrogenuse efficiency, nitrogen cycling occurs at region scale and policies can be implemented and enforced atthe national or provincial/state levels. Multinational efforts to control N loss to the environment are surelyneeded, but these efforts will require commitments from individual countries and the policy-makers withinthose countries.

The present booklet dealing with ‘Reactive Nitrogen in Agriculture, Industry and Environment inIndia’ is the third in the IGBP-WCRP-SCOPE series, and presents an overview of reactive nitrogen inagriculture, industry and environment in India. The information compiled by the authors should helpplanners in agriculture, industry and energy production to guide future expansion in the economy in away that the delicate balance between inputs and outputs of reactive nitrogen in the environment ismaintained.

Date: January, 2008 M VijayanPlace: New Delhi President

Indian National Science Academy

Reactive Nitrogen in Agriculture, Industry and Environment in India iii

4 Bijay Singh, MK Tiwari and YP Abrol

BLANK

Reactive Nitrogen in Agriculture, Industry and Environment in India 5

Fax: (0542) 2368174 Phones: (Off) (0542) 2368399E-mail: [email protected] (Res) (0542) 2369093

[email protected] (Mob) +91 9335178355

BANARAS HINDU UNIVERSITYEcosystems Analysis Laboratory

J.S. SINGH PhD FTWAS FNA FASc FNASc DEPARTMENT OF BOTANYVARANASI-221005, INDIA

Preface

While majority of the Indian agricultural soils are deficient in usable forms of nitrogen, uneven/excessive/improper/inappropriate use of N fertilizers, coupled with contributions from industrial effluents/exhausts,animal wastes and geo-deposits have led to widespread pollution of groundwater and eutrophication ofsurface waters posing a severe problem for public health and the ecosystem. The ozone-depleting andgreenhouse effects of NOx gases from various farm and non-farm sources may pose new concerns fornitrogen-carbon balance. There is no escape from the use of fertilizers to sustain food production, andthe environmental consequences of accumulation of reactive N are the same, regardless of whether thefertilizers are of chemical or biological origin. Therefore, the challenge now facing Indian agriculture isto further enhance the productivity of our agricultural system without adversely impacting our environmentand ecology. This necessitates an integrated understanding of nitrogen in India’s agriculture, industry andenvironment so as to identify the appropriate sites for intervention towards a more sustainable Nmanagement regime.

At the request of the IGBP-WCRP-SCOPE National Committee, Professor Y.P. Abrol a pioneer researcherin the area of reactive nitrogen and Fellow of the Indian National Science Academy, agreed to distill thecurrent thinking in India with regard to various aspects of the nitrogen cycle with special reference toreactive N in the lndian context, and to summarise the current knowledge as well as identify the gapsin it for informed decisions on further research and policy. Professor Abrol chose two coauthors on thebasis of their expertise, strong and long presence in the field, and commitment to interdisciplinaryunderstanding on various aspects of nitrogen.

The article provides state-of-the-art review integrating global literature and India-specific information asappropriate. I am sure the material provided here will be of use to scientists and science students interestedin SCOPE and IGBP.

J S SinghChairman,IGBP-WCRP-SCOPE National Committee

v


Contents

Foreword .... iii

Preface .... v

Abstract .... 1

Outline .... 1

Reactive nitrogen – definition and scope .... 2

Nitrogen fluxes, cycle and cascade effects .... 5

Nitrogen fluxes and cascade effects in India .... 5

Reactive nitrogen in Indian agriculture .... 8

Reactive nitrogen from use of fossil fuels in industry, transport and energyproduction in India .... 18

Atmospheric nitric oxide (NO) and nitrous oxide (N2O) .... 22

Emission of reactive nitrogen as ammonia from terrestrial ecosystems .... 24

Nitrate-nitrogen in groundwater bodies .... 26

Nitrogen in rivers, coastal ecosystems and oceans .... 32

Challenges and options for mitigation of environmentallyimportant reactive nitrogen, research and planning .... 34

References .... 36


Reactive Nitrogen in Agriculture, Industry andEnvironment in India

Molecular form of nitrogen (N2) is unusable by the vast majority of living organisms. It must be transformedor fixed into other forms collectively known as reactive nitrogen which includes all biologically, chemicallyand radiatively active nitrogen compounds in the atmosphere and biosphere. The flows of reactive N in terrestrial,aquatic and atmospheric ecosystems in India are being increasingly regulated by inputs, use efficiency andleakages of reactive N from agriculture and growing use of fossil fuels for energy. In the last three decades,use of reactive N in the form of chemical fertilizers has kept pace with production of food grains and at presentmore than 11 Tg is being applied annually to agroecosystems in the country. As for cereal-based agriculture,recovery of N by rice and wheat at on-farm locations in India rarely exceeds the 50% mark so that a largeportion of total N fixed biologically, applied as fertilizers or recycled as organic manures leaves agroecosystemsto reach atmosphere or aquatic realms. The greatest challenge in improving N use efficiency lies in developingprecision management of reactive N in time and space. Coal burning power plants and combustion of oilin road transport contributed up to 33% each in total NOx emissions in India. With around 49% growthas compared with levels in 2000, NOx emissions are estimated to be more than 7 Tg in 2020. Agriculturalactivities in India account for more than 80% of the total N2O emissions – including 60% from the use ofN fertilizers and 12% from burning of agricultural residues. Application of fertilizers and the livestock in agriculturesector are the major contributors to NH3 emissions. In Asia, reactive N transfers to the atmosphere by NH3volatilization are expected to reach 19 Tg N year–1 in the next three decades; 29% being India’s contribution.With very high groundwater development along with high fertilizer N use, the northwestern region in thecountry has been categorized as the high risk zone for nitrate-N pollution of groundwater bodies. At severalplaces sources other than fertilizer N are more important for high nitrate-N levels in groundwater. ReactiveN is being exported in the form of nitrate out of watersheds of river Ganga at the rate of 601 kgN year–1 km–2. Total reactive N in annual river runoff from South Asia amounts to more than 4 Tg. Of thisaround 30 % is added to Arabian Sea adversely affecting its biogeochemical processes. Use of increasingamounts of reactive N in the form of fertilizers in Indian agriculture and efficient management of fertilizerN will remain at the forefront of issues to improve the reactive N balance over both the short- and long-term. Reactive N emissions from fuel combustion (NOx) can be reduced by following strict policies but reducingthe introduction of new reactive N in food production seems to be very difficult in countries like India havingburgeoning populations. It is now technically feasible to decrease reactive N creation from fossil fuel combustionto a point where it becomes just a minor disturbance to the reactive N cycle. Challenge ahead is to followthe three stage strategy of the International Nitrogen Initiative in terms of assessing knowledge of N flows,developing region specific solutions and implementing scientific, engineering and policy tools.

OUTLINE

Nitrogen is necessary for all forms of life and a crucial component in the increased production of foodto feed the continuously increasing human and animal populations. In many ecosystems on land andsea, the supply of nitrogen controls the nature and diversity of plant life, the population dynamics ofboth grazing animals and their predators, and vital ecological processes such as plant productivity andthe cycling of carbon and soil minerals. This is true not only in wild or unmanaged systems but in mostcroplands and forestry plantations as well. We live in a world surrounded by nitrogen but more than99% of this nitrogen is not available to more than 99% of living organisms. It is all about having enoughof right kind of nitrogen, often called reactive or ‘fixed’ nitrogen converted from the non-reactive N2 formthat determines such fundamentals of life as the extent of plant growth which in turn determines to alarge extent the dynamics of food supply. Since the beginning of the last century, mankind has injectedincreasing amounts of reactive nitrogen into the environment, intentionally as fertilizer and unintentionallyas a by-product of combusting fossil fuels. As a result nitrogen cycle is being altered causing possible


grave impacts on biodiversity, global warming, water quality, human health, and even the rate of populationgrowth in several parts of the world.

Nitrogen cascade, defined as the sequential transfer of nitrogen through environmental systems(including temporary storage within each system), leads to multiple linkages among the ecological systemsmagnifying the consequences and human health effects of nitrogen. Of course, still there are regions indeveloping world, where still not enough reactive nitrogen is available to sustain the human population.Human activities are responsible for a large proportion of emissions of nitrogen-containing trace gases,including 40% of the nitrous oxide, 80% or more of nitric oxide, and 70% of ammonia releases on aglobal basis. The result is increasing atmospheric concentrations of the greenhouse gas nitrous oxide,of the nitrogen precursors of smog, and reactive nitrogen that falls from the atmosphere to fertilizeecosystems. The burning of fossil fuels such as coal and oil releases previously fixed nitrogen from long-term storage in geological formations back to the atmosphere in the form of nitrogen-based trace gasessuch as nitric oxide. High-temperature combustion also fixes a small amount of atmospheric nitrogendirectly. Altogether, the operations of automobiles, factories, power plants, and other combustion processesemit more than 20 Tg per year of fixed nitrogen to the atmosphere. According to an estimate out oftotal emission of 26.77 million tons of NOx in Asia, China and India accounted for 42 and 17% of theemissions in the year 2000. It is also estimated that by 2020, India alone will be contributing NOx tothe tune of 7.1 million tons annually from road and rail transport sectors. Greatly increased transportof reactive nitrogen by rivers into estuaries and coastal waters is also a matter of great concern as reportsare already pouring in regarding O2-deficiency in Indian coastal waters due to enhanced nitrogen loadingfrom land. Since ill effects of excessive reactive nitrogen such as green house effect and damage to ozonelayer due to emission of N2O or acid rain are not confined to political boundaries, developing countrieslike India and China which need to support huge populations by producing enough food by increasinguse of nitrogen fertilizers will remain in the eyes of the world until and unless some remedial measuresare taken right now.

The reactive nitrogen is now attracting increased attention from scientists, environmentalists,governments and industry. Excess nitrogen in our environment represents a human perturbation of thenatural cycle of nitrogen in the environment. Industrial emissions of nitric oxide to the atmosphere mustbe reduced as soon as possible. The problem of excess nitrogen can be addressed by more judiciousand efficient applications of nitrogen fertilizer in agriculture, and by better management of wetlandecosystems that return nitrogen to the atmosphere in its nearly inert or unreactive form, N2. In fact itis the ultimate goal of the scientific community to provide policy makers with reliable estimates of reactivenitrogen transfers to different ecosystems and to describe balanced, cost-effective and feasible strategiesand policies to reduce the amount of reactive nitrogen where it is not wanted.

REACTIVE NITROGEN – DEFINITION AND SCOPE

Nitrogen as it exists in its inert state as N2 - is the most abundant element in the earth’s atmospherebut, in this form, is almost wholly unusable by the vast majority of living organisms. It must be transformedinto a variety of other forms, together called “reactive nitrogen”, in order to be biologically functional.The diverse pool of nitrogen forms termed as reactive nitrogen includes all biologically, chemically,radiatively and/or photochemically active nitrogen compounds in the atmosphere and biosphere (Gallowayet al., 1995). It includes forms of nitrogen, such as ammonia (NH3) and ammonium (NH4

+), nitric oxide(NO), nitrogen dioxide (NO2), nitric acid (HNO3), nitrous oxide (N2O), and nitrate (NO3

–), and organiccompounds such as urea, amines, proteins and nucleic acids. Structure and functioning of terrestrial,


freshwater and marine ecosystems and chemistry and/or radiative balance of the atmosphere are alteredby the availability of reactive N (Vitousek et al. 1997).

Reactive nitrogen can be created both through natural processes and anthropogenically. Under naturalconditions, the triple bond that binds two nitrogen atoms together as N2 is broken either by lightningor by microbes able to carry the process known as biological nitrogen fixation (BNF). In the oceans BNFis carried out primarily by cyanobacteria, commonly known as blue green algae. Prior to mid-19th century,the supply of reactive N for food production was either through BNF, animal manures, rotation of cropsor fallow and it could support the small human population existing during those times. Thereafter withgrowth of human population at a very high rate, these sources could not support the needed expansionof agriculture. In 1900s Haber-Bosch process was invented and it allowed mass production of fertilizerby synthesizing ammonia from nitrogen and hydrogen. Even after 100 years, this process remains themost economical anthropogenic means of creating reactive nitrogen and is responsible for sustaining nearly40 % of the current world population due to its ability to increase crop yields (UNEP and WHRC, 2007).Where there is not enough reactive nitrogen, soil fertility declines, serious land degradation may occur,and agricultural productivity is reduced. As a consequence, populations that rely directly on these agriculturalsystems cannot produce enough food to survive. However, where too much reactive nitrogen has beenintroduced by humans, its positive outcomes can be outweighed by negative ones, ultimately threateningthe very ecosystems it initially supports.

Reactive nitrogen can swiftly move among different media of air, soil and water. It can contributeto higher levels of ozone in the lower atmosphere, causing respiratory ailments and damaging vegetation.A portion of reactive nitrogen is converted to nitrous oxide which contributes to both the greenhouseeffect and to stratospheric ozone depletion. From the atmosphere, it can fall to the surface as atmosphericdeposition which leads to acidification of soils and water bodies, and inadvertent fertilization of treesand grasslands, creating unnatural growth rates, nutrient imbalances, decreasing or altering biodiversityand corrosion of buildings, bridges and other human made structures,. Leaching out of the soils, reactivenitrogen can reach groundwater and surface water bodies making them unfit for human consumptionor use. Reactive nitrogen also promotes eutrophication in coastal ecosystems, which can negatively impactfish stocks and biodiversity. Eventually, most reactive nitrogen is denitrified back to molecular nitrogen.Abrol et al. (2007) have compiled salient features of cycling of N originating from agrecosystems in terrestrial,aquatic and atmospheric realms in India.

The most common forms of inorganic nitrogen in the environment are diatomic nitrogen gas (N2),nitrate (NO3

– ), nitrite (NO2–), ammonia (NH3) and ammonium (NH4

+). The species that predominatedepend on the chemical, physical, and biological environment. Some reactive N species important inthe context of food production, fossil fuel combustion and environmental degradation are describedbelow:

NH4+ and NO3

– (ammonium and nitrate): The two ionic species of reactive N are abundantly presentin soil solution of terrestrial ecosystems. Roots of plants take N as NH4

+ and/or NO3– from soil solution.

Plants can take both the ionic species with equal ease but relative abundance of the two species in thesoil solution is governed by factors such as pH, Eh, aeration status and texture of the soil. At any time,concentration of NH4

+ and NO3– in the soil solution is low but as these are taken up by plant roots

these are replenished through mineralization of soil organic matter and organic manures or throughapplication of N fertilizers such as urea, ammonium sulphate, calcium ammonium nitrate and anhydrousammonia. Role of reactive N in food production is governed by supply of NH4

+ and NO3– to crop plants

through biological and anthropogenic sources.


Nitrate-N in the soil solution can be lost from the root zone via leaching when water percolatesdown the soil profile and reach natural water bodies. Nitrate-N is also denitrified to N2O and N2 if anaerobicconditions occur in the soil and there is sufficient supply of C to denitrifiers. Ammonium-N is readilyadsorbed on soil exchange complex and does not move down the profile in large amounts. However,it gets converted to NH3 gas if along with high soil pH soil surface gets dried and weather is windy (BijaySingh and Yadvinder Singh, 2003).

NOx (nitrogen oxides): Generic term used for a group of highly reactive gases containing nitrogen andoxygen in varying amounts. Nitrogen oxides are formed when fuel is burned at high temperatures, asin a combustion process. The primary man made sources of NOx are motor vehicles, electric utilities,and other industrial, commercial, and residential sources that burn fuels. NOx can also be formednaturally. Depending upon excess air used during combustion and the gas temperature in the boiler, nitricoxide (NO) is produced in thermal power plants by the oxidation of atmospheric nitrogen duringcombustion of the fuel. The contribution of nitrogen contained in the fuel in the production of NO isvery small. Most of the nitrogen oxides are colorless and odorless. Only exception seems to be nitrogendioxide (NO2) which along with particles in the air can be seen as a reddish-brown layer over manyurban areas.

Nitrogen oxides can be transported over long distances and is one of the main ingredients involvedin the formation of ground-level ozone (lowest part of atmosphere extending up to between 8 and 16km high), which can trigger serious lung damage and respiratory problems. Ozone production in thetroposphere is mainly due to the oxidation of CH4, CO and hydrocarbons in the presence of NOx (Crutzen,1974; Chameides and Walker, 1973). NOx reacts to form nitrate particles, acid aerosols, as well as NO2,which also cause respiratory problems. It contributes to formation of acid rain and to nutrient overloadthat deteriorates water quality. NOx can contribute to atmospheric particles that cause visibilityimpairment. NOx indirectly influences the radiation budget of the atmosphere through O3, which possiblyrepresents 10–15% of the total anthropogenic greenhouse radiative forcing in the atmosphere (Laciset al., 1990, Wild et al., 2001). NOx also influences the oxidation capacity of the atmosphere throughOH and nitrate.

NH3 (ammonia): The atmosphere receives reactive N in the form of NH3 from aquatic and terrestrialecosystems. In the atmosphere it is either deposited or transformed into an ammonium aerosol. Beforedeposition, ammonium aerosols contribute to fine particulate matter and regional haze concentrationsin the atmosphere. According to Seinfeld and Pandis (1998) and Penner et al. (2001), ammonia playsan important role in the direct and indirect effects of aerosols on radiative forcing and thus on globalclimate change.

N2O (nitrous oxide): When emitted into the atmosphere it disperses and is not rapidly deposited backto the ground like NOx or ammonia. It has a troposphere residence time of approximately 100 yearsand is increasing at a rate of 0.2–0.3% per year (Prather et al., 2001). On a molecule for molecule basis,N2O has a global warming potential over 200 times greater than that of CO2. Nitrous oxide is a greenhousegas in the troposphere but some nitrous oxide makes its way up into the stratosphere where it has anotherundesirable effect - it contributes to thinning of the ozone layer. Destruction of stratospheric ozone, whichprotects us from harmful effects of UV radiation, is caused by chlorine and bromine released fromhalocarbons - the CFCs that have been so widely used in refrigeration, in aerosol cans, insulation andflame retardants. Nitrous oxide plays its part when it is converted to nitric oxide which acts as a catalystin the reactions in which chlorine and bromine destroy ozone.


NITROGEN FLUXES, CYCLE AND CASCADE EFFECTS

Nitrogen cycle consists of transformations of molecular nitrogen through fixation into forms of reactivenitrogen, including those which support the earth’s biota, and back to its molecular state throughdenitrification. The cycling of nitrogen among its many forms is a complex process that involves numeroustypes of bacteria and environmental conditions. The natural nitrogen cycle has been altered through humanactivity in terms of creation of artificial processes to produce more reactive nitrogen to support increasedlevels of agriculture. In general, the nitrogen cycle has five steps: (1) nitrogen fixation (N2 to NH3/ NH4

+

or NO3–), (2) nitrification (NH3 to NO3

–), (3) assimilation (incorporation of NH3 and NO3– into biological

tissues), (4) ammonification (organic nitrogen compounds to NH3) and (5) denitrification (NO3– to N2).

The creation of reactive nitrogen occurs both through natural processes and through humaninterventions. Biological nitrogen fixation (BNF) constitutes transformation of gaseous nitrogen into usableor reactive forms by microbes often existing in a symbiotic relationship with leguminous plants. In theoceans, BNF is carried out primarily by cyanobacteria, commonly known as blue-green algae.Anthropogenically, Haber-Bosch process is used to synthesize ammonia from nitrogen and hydrogen gasesand nearly 100 years after its invention, it still remains the most economical means of fixing nitrogen.Nitrification is a two-step process in which NH3/ NH4

+ is converted to NO3–. First, the soil bacteria

nitrosomonas and nitrococcus convert NH3 to NO2–, and then another soil bacterium, nitrobacter, oxidizes

NO2– to NO3

–. Assimilation is the process by which plants and animals incorporate the NO3– and NH4

+

formed through nitrogen fixation and nitrification. Plants take up these forms of nitrogen through theirroots, and incorporate them into plant proteins and nucleic acids. Animals are then able to utilize nitrogenfrom the plant tissues. Assimilation produces large quantities of organic nitrogen, including proteins, aminoacids, and nucleic acids. Ammonification is the conversion of organic nitrogen into ammonia. The ammoniaproduced by this process is excreted into the environment and is then available for either nitrificationor assimilation. Denitrification is the transformation of reactive nitrogen back to inert gaseous nitrogenin the atmosphere, carried out primarily by bacteria in soils and water bodies.

Nitrogen cascade is a sequence of effects when excessive reactive nitrogen, in its many forms, readilymoves among terrestrial, aquatic and atmospheric realms accumulating a series of primarily negativeenvironmental consequences for ecosystems and human health. In Figure 1 Galloway et al. (2003) hasshown multiple linkages among ecological and human health effects of reactive nitrogen molecules asthey move from one environmental system to another.

NITROGEN FLUXES AND CASCADE EFFECTS IN INDIA

Using data from different sources (Bhatt, 2002; FAI, 2000; Agricultural Statistics at a Glance, 1999),Velmurugan et al. (2008) attempted to quantify different nitrogen fluxes involved in N cycle in agroecosystemsin India. The data shown in Figure 2 were worked out for 1995-96 reference period. In the absenceof reliable quantitative studies, large uncertainties were associated with many estimates shown inFigure 2, but these seem to be very good estimates to begin with. As better quantification of differentprocesses and fluxes associated with reactive nitrogen in India become available, improved versions ofnitrogen cycle and cascade effects will become possible in the years to come.

In 1995-96, 10.8 Tg N was applied as nitrogenous fertilizers to agricultural soils in India; another1.14-1.18 Tg N was added through biological nitrogen fixation. Velmurugan et al. (2008) estimated thesoil N pool other than forest to be as large as 1046 to 2581 Tg N. The proportion of N contained insoil which is actively recycled in the soil-plant system is not known with certainty. Crude estimates showthat Indian agricultural systems produce annual harvest that removes ~4.13 Tg N from the total crop


N pool of ~12.47 Tg N. Further, ~1.9 Tg N is removed from the crop N pool and used for fuel, whichin turn released N2O into atmosphere. The nitrogen contained in plants was either recycled or was suppliedto consumers such as animals (~5.81 Tg N) or people (~0.57 Tg N). India has the largest livestockpopulation in the world and the livestock biomass N pool was estimated to be ~1.62 Tg of N. The animalsin turn may return a portion of the N to the system as manure. Animals, such as birds or insects alsoharvest some N and may return it to the system as excreta and corpse which are difficult to estimate.Organic manure is one of the important sources of N used in crop production. It is produced from crop,animal and human wastes and added ~0.17 Tg N to the soil during 1995-96.

The wet N deposition (NO3– and NH4

+) in agricultural soils in India during 1995-96 as estimatedby Velmurugan et al. (2008) worked out to be ~0.81 Tg N. Nitrate N leaching beneath agricultural soilsand through runoff was estimated to be ~0.06 Tg N. This agricultural leaching and run-off results innitrate pollution of ground water bodies or N enrichment of river systems. Since irrigation is one of theessential components of modern agricultural production systems, ground water is utilized to irrigate~36.25 M ha in India. As a result, 0.11 Tg N in the form of NO3

– contained in the ground water isbrought back into the agricultural production system. About 25% of N reaching river systems is expectedto end up in the sea. The concentration of NO3

–, NO2– and NH4

+ in the surface waters of mangrovesin the eastern coast of India near Chennai was found to be very high (35.3, 23.0 and 157μg of the chemicalspecies l–1 respectively) which are associated with regions receiving agricultural wastewater from land-based sources (Velmurugan et al. (2008).

Fig. 1: Illustration of the nitrogen (N) cascade showing the sequential effects that a single atom of N can have in variousreservoirs after it has been converted from a nonreactive to a reactive form. Abbreviations: GH- greenhouse effect;

NH3– ammonia; NO3

– - nitrate; NOx- nitrogen oxide; N2O- nitrous oxide; PM- particulate matter (Source: Galloway et al., 2003)


There is substantial movement of N in and out of India from neighbouring countries through windand water flows but reliable estimates are hardly available. In 1995-96, 0.07 Tg N comprising food grains(0.02 Tg N) and animal products (0.05 Tg N) was imported and 0.11 Tg N comprising food grains (0.09Tg N) and animal products (0.02 Tg N) was exported from India (Velmurugan et al., 2008). FertilizersN import which account for 2.00 Tg N (1995-96) is not included in this estimate, but added to the Nfertilizer addition into the soil. The detailed estimation methodology, individual products and N equivalentsare given by Bhatt (2002).

Total N2O emissions from India were in the order of 0.23 Gg in 1990 and 0.26 Gg in 1995 indicatinga marginal growth (Garg et al., 2001). National estimate of N2O emission from manure use is lackingand most of the research focuses on point/experimental field emission of N2O. Further, reliable estimateof manure use in agriculture in various districts of the country is hardly available and the existing N2Oemission data at national level is estimated using Inter-governmental Panel on Climate Change (IPCC)emission co-efficient. The uncertainties associated with such data sets are high as single co-efficient basedestimate can not be reliable.

The NOx emission from India in 1995 was estimated to be 3.46 Tg and grew at about 5.6% perannum between 1990 and 1995 (Garg et al., 2001a). The regional distribution also indicated a closerelationship with coal as well as oil products consumption. Uttar Pradesh, Maharashtra, Madhya Pradesh,Andhra Pradesh and Tamil Nadu were the largest five NOx emitting states in 1995 (Garg et al., 2001b).Total NH3 emission in 2000 was reported to be 7.4 Tg which is 27% of Asian emission (Streets et al.,

Fig. 2: Simplified N cycle in agro-ecosystem of India (Velmurugan et al., 2008)


2003). The volatilization of applied N as NH3 and NOx is followed by deposition as ammonium (NH4)and oxides of nitrogen on soils and water and accounts for indirect NO2 emissions from soils (NATCOM,2004).

REACTIVE NITROGEN IN INDIAN AGRICULTURE

Agriculture is the mainstay of the Indian economy and it contributes about 22 percent of the gross domesticproduct and provides a livelihood to two-thirds of the population. Although livestock rearing is complementaryto agriculture, India has a huge live stock population of over 480 M (IASRI, 2006). The total area undercultivation is 169.7 M ha; an additional area of 0.4 M ha is under plantation crops (FAOSTAT, 2007).To meet the food needs of the burgeoning population, India will have to increase the production of foodgrains from the present level of 215 M t to 300 M t by 2020. It is an uphill task because prospects forexpanding irrigation, one of the driving forces behind yield increases, are becoming limited as are theprospects for converting marginal lands into productive arable land. New technologies such as geneticallyengineered, yield-increasing plants are also not expected to play major roles in increasing food productionin developing countries during the next two decades. This scenario suggests that future increases inproduction of rice, wheat and other cereals will continue to depend heavily on increased use of nutrients,particularly N, in each hectare of the land under agriculture. Indeed, fertilizer N - an essential componentof green revolution in India – has lead to a tremendous increase in food production since 1960’s.Consequently, despite large population increases over the same time period, starvation and malnutritionhave declined.

Forms of N (NO3– and NH4

+) which are taken up by plants can be made available for crop productionthrough chemical fertilizers, natural and anthropogenic biological N fixation and through recycling of plantand animal wastes. Fate of reactive N in agroecosystems assumes great importance because reactive Nfixed biologically or applied as fertilizer not only leads to increased crop production but can also get leakedfrom agroecosystems depending on how efficiently it has been used by crop plants. Portion of reactiveN emitted from agroecosystems end up in the form of N2O, NH3, NOx gases, leached as nitrate intoground and surface water bodies and can reach the coastal waters through rivers; these forms of leakedreactive N may lead to significant costs to society.

Industrial fixation of N for use as fertilizer represents by far the largest human contribution of newreactive N to N-cycle. Already, the quantity of fertilizer N used in India during the last 11 years (1995to 2005) is equal to the total quantity used up to 1994 (FAI, 2005). Area under cereal crops and N useefficiency are the two major drivers of future N fertilizer consumption in the country. During 1960 to1990, genetic improvements leading to development of highly fertilizer-responsive rice and wheat varietiesand improved management strategies resulted in a dramatic rise in productivity and production fromrice and wheat in India. For example, more than 75% of the total food grains produced in the countryare rice and wheat (FAI, 2005) and use of nitrogen fertilizers has contributed much to the remarkableincrease in production of rice and wheat in India during more than five decades (Fig. 3).

In the years to come, agriculture in India is going to witness a very delicate balance between inputsand outputs of reactive N. On the one hand, the demand of burgeoning population for enough and highprotein food will require substantial reactive N inputs into agroecosystems through chemical fertilizers,biological N fixation and recycling of organic wastes. But on the other hand, to ensure minimal leakageof reactive N from agriculture to other ecosystems, reactive N must be used efficiently to produce morefood with less reactive N inputs.


Reactive Nitrogen Inputs in Indian Agriculture

Using the approach followed by Parris and Rielle (1999) for some of the OECD (Organisation for EconomicCo-operation and Development) countries, Prasad et al. (2004) computed soil surface N balance foragricultural land of India for the year 2000-01. Fertilizer N input was calculated by summing the area-weighted portion of fertilizer sold in each state and multiplying by the N content of the fertilizer. Livestockmanure N production from different states was calculated as the number of live animals distinguishedin terms of general species (sheep, goats, cattle, buffaloes, horses, mules, donkeys, camels, pigs, poultry,yaks) (Agricultural Statistics at a Glance, 2003) multiplied by respective N excretion coefficients for theAsian region as given by the Intergovernmental Panel on Climate Change (IPCC,1996). That a largeproportion of animal excreta is not converted to manure and is used for other purposes was not consideredin working out N contributions from livestock manure. Although livestock manures represented a transferof already-fixed N from one place to another rather than addition of new reactive N, the data inTable 1 presents a complete picture of reactive N inputs to agricultural land in India. Interestinglyfertilizer N and biological N fixation – the sources of new reactive N constituted only 44 % of the totaladditions.

Fig. 3: Production of rice or wheat in relation to fertilizer N use in India during 1951 to 2004 (Source: FAI, 2005)

Table 1. Inputs of reactive N to surface soil of agricultural land of India during 2000-2001

Inputs Total N kg N ha-1

Tg % contribution

Inorganic fertilizers 11.50 32.48 57.76

Livestock manure 15.60 44.06 130.17

Nitrogen fixation 4.10 11.58 17.10

Atmospheric deposition 4.20 11.86 31.81

Source: Prasad et al. (2004)


The consumption of fertilizers varies significantly from state to state. The all-India per-hectareconsumption of fertilizer N was 59.2 kg in 2003/04 (FAO, 2005). While the North zone had aconsumption of more than 100 kg N ha–1, in the East and West zones the consumption was lower than50 kg ha–1 (Table 2). Among the major states, the per-hectare consumption of fertilizer N was more than100 kg in Punjab and Haryana. In Assam, Chattisgarh, Himachal Pradesh, Jammu and Kashmir, Kerala,Madhya Pradesh, Maharashtra, Orissa and Rajasthan, N consumption per hectare was lower than theall-India average of 59.2 kg ha–1. Rice occupied an area of 44.7 M ha and it accounted for 31.8 %(5.34 M t) of total fertilizer consumption in India during 2003/04 (Table 3). Fertilizer N use on irrigatedrice (103 kg ha–1) is almost double that on rainfed rice (56 kg ha–1). Wheat, grown largely under irrigatedconditions, accounts for 20.5 % (3.44 M t) of total fertilizer consumption in India. Fertilizer use per hectarein 2003/04 was: 137 kg (100 kg ha–1 N, 30 kg ha–1 P2O5 and 7 kg ha–1 K2O). Fertilizer use on irrigatedwheat (144.9 kg ha–1) is almost double that on rainfed wheat and the trend is similar for all the nutrients.Table 4 reveals that during 1999/2000 to 2003/04, 93.7 to 100 % of fertilizer N applied to agriculturalland was produced in India.

Nitrogen inputs from biological N fixation (field beans, soybeans, clover, alfalfa, pasture) as reportedin Table 1 were obtained from dry biomass production multiplied by the fraction of N in nitrogen-fixingcrops (Prasad et al., 2004). Area under green manuring was about 7 M ha (FAO 2005). BiologicalN fixation was found to be high in Andhra Pradesh (71.2 kg N ha–1) followed by Madhya Pradesh(38.7 kg N ha–1), Maharashtra (36.5 kg N ha–1) and Orissa (34.4 kg N ha–1). The use of biofertilizersis of relatively recent origin. Biofertilizers consist of N fixers (Rhizobium, Azotobacter, blue green algae,

Table 4. Production, import and consumption of fertilizer N in India (000’ t)

1999/2000 2000/01 2001/02 2002/03 2003/04

Production 10,873 10,943 10,690 10,508 10,575

Import 856 164 283 135 205

Consumption 11,593 10,920 11,310 10,474 11,076

Source: FAO (2005)

Table 2. Consumption of fertilizer (kg ha-1) in four zones of India during 2003/04

Zone Fertilizer N Fertilizer N+P2O5+K2O

East (Assam, Bihar, Jharkhand, Orissa, West Bengal) 49.0 75.8

North (Haryana, Himachal Pradesh, Jammu and Kashmir, Punjab, 102.9 140.1Uttar Pradesh, Uttranchal)

South ( Andhra Pradesh, Karnataka, Kerala, Tamil Nadu) 60.0 105.4

West ( Chattisgarh, Gujarat, Madhya Pradesh, Maharashtra, Rajasthan) 38.0 59.4

All India 59.2 89.8

Source : FAO (2005)

Table 3. Fertilizer use in rice and wheat during 2003-04 in India (Source: FAO, 2005)

Crop Gross cropped Share in fertilizer Fertilizer consumption (kg ha-1)area (M ha) consumption (%) N P2O5 K2O Total

Rice–irrigated 24.0 22.2 103.4 32.8 18.8 155.0

Rice–rainfed 20.7 9.6 56.6 14.5 6.5 77.6

Wheat–irrigated 22.8 19.7 105.6 32.1 7.3 144.9

Wheat–rainfed 2.9 1.3 55.7 15.9 4.3 75.9


Azolla) and fungi (mycorrhizae). A contribution of 20–30 kg N ha–1 has been reported from the use ofbiofertilizers under Indian conditions (FAO, 2005).

The use of organic manures is the oldest and most widely used practice of nutrient replenishmentin India. Prior to the 1950s, organic manures were almost the only sources of reactive N other thanatmospheric N deposition. Organic manures make a significant contribution to the supply of plant nutrientsand soil fertility. Since production of manure is dictated by livestock population, distribution and densityacross states and regions of the livestock population are important to study N balances. However, it shouldbe taken into account that a substantial proportion of cattle excreta is used for purposes other than supplyingnutrients. Thus estimates of total N inputs to agricultural soils as calculated in Table 1 by Prasad et al.(2004) seem to be on a higher side. At the present production level, the estimated annual productionof crop residues is about 300 M t. As two-thirds of all crop residues are used as animal feed, only one-third is available for direct recycling (FAO, 2005). The production of urban compost had been180.8 M t during 1996-97 (IASRI, 2006). In addition to improving soil physical and chemical properties,the supplementary and complementary use of organic manure also improves the efficiency of mineralfertilizer use.

Nitrogen Use Efficiency in Agroecosystems

During the last half-decade while fertilizer N consumption in India is touching new heights, the productionof both rice and wheat is plateauing (Fig. 4). In fact, fertilizer N efficiency in food grain production expressedas partial factor productivity of N (PFPN) has been decreasing exponentially since 1965 (Fig. 5). ThePFPN is an aggregate efficiency index that includes contributions to crop yield derived from uptake ofindigenous soil N, fertilizer N uptake efficiency, and the efficiency with which N acquired by the plantis converted to grain yield. A decrease in PFPN occurs as farmers move yields higher along a fixedN response function, unless other factors shift the response function up. The low PFPN during the lastdecade is due to low fertilizer N uptake efficiency and is of particular concern for the reactive N budgetbecause fertilizer N use in India is continuously increasing (Fig. 4). Cassman et al. (2002) defined the

Fig. 4: Time trends of fertilizer N consumption vis-à-vis area and production of rice and wheat in India (Source: FAI, 2005)


overall N use efficiency as the proportion of N inputs that are removed in harvested crop biomass, containedin recycled crop residues and incorporated into soil organic matter and inorganic pools. Applied N notrecovered in these sinks is prone to loss from the cropping system via leaching, denitrification andvolatilization and contributes to reactive N load that cascades through environment external to theagroecosystem.

Nitrogen contributions from soil in a given year/season and on a long-term basis can greatly alterapparent recovery efficiency of applied N (REN) because there occurs a large fertilizer N substitution ofsoil N. Although both indigenous soil resources and applied fertilizer N contribute to plant available Npool consisting of NO3 and NH4 ions, this pool represents a very small fraction of total soil-N. The amountof N derived from indigenous resources during a single cropping cycle typically ranges from 30-100 kgN ha–1 that represents only 1.5 to 5% of total soil N. The overall fertilizer N use efficiency can be increasedby achieving greater REN, by reducing the amount of N lost from soil organic or inorganic pools, or both.When soil-N content is increasing, the amount of sequestered N contributes to higher N use efficiencyand the amount of sequestered N derived from applied N contributes to a higher REN. Conversely, anydecrease in soil N stocks will reduce overall N use efficiency and REN.

A recent review on N use efficiency (Ladha et al., 2005) reported average single-year fertilizer Nrecovery efficiencies as 57% for wheat and 46% for rice in researcher managed experimental plots. Nitrogenrecovery in crops grown by farmers, however, is often much lower. A review of best available informationsuggests that average N recovery efficiency for fields managed by farmer’s ranges from 20-30% underrainfed conditions and 30 to 40% under irrigated conditions. Nitrogen use efficiency exceeding 40% isexpected to occur in response to improved N management practices. Cassman et al. (2002) found thatN recovery from on-farm locations averaged 31% for irrigated rice in Asia and 40 % for rice under fieldspecific management. For wheat grown in India, the recovery averaged 18% under poor weather conditionsbut 49% when grown under good weather conditions (Table 5). Ladha et al. (2005) compiled data on15N recovery by cereal crops and found that average REN 15N was 44% in the first growing season andtotal recovery of 15N fertilizer in the first and five subsequent crops was only around 50%.

Fig. 5: Fertilizer N efficiency of food grain production (annual food grain production divided by annual fertilizerN application) during 1965 to 2004 in India (Source: FAI, 2005)

0

20

40

60

80

100

120

140

160

180

1960 1970 1980 1990 2000Year

M t

food

gra

in/M

t N

fert

ilize

r


Management options to enhance fertilizer N use efficiency in agroecosystems has been describedin details by Acharya and Sharma (2007), Pathak and Ladha (2007) and Yadvinder-Singh et al. (2007).Fertilizer N use efficiency is controlled by crop demand for N, supply of N from the soil, fertilizers andmanures, and losses of N from the soil-plant system (Balasubramanian et al., 2004). Crop N demandis the most important factor influencing fertilizer N use efficiency. It is determined by biomass yields andphysiological requirements of tissue N. Solar radiation, temperature and moisture regimes determine thegenetic yield ceiling but actual crop yields are far below this threshold because it is neither possible, noreconomical to remove all limitations to growth. Hence, the interaction of climate and management causestremendous year-to-year variation in on-farm yields and crop N requirement. Physiological N efficiency- the change in grain yield per unit change in N accumulation in aboveground biomass is controlledby mode of photosynthesis (C3 or C4 photosynthetic pathway) and grain N concentration that is alsoinfluenced by N supply (Cassman et al., 2002).

Losses of Reactive Nitrogen from Agroecosystems

Reactive nitrogen leaves agroecosystems through leaching of inorganic nitrate or dissolved forms oforganic N, or through gaseous emissions to the atmosphere in the forms of NH3, NO, N2O, or N2.Essentially, all emitted NH3 is returned to the surface by deposition (van Breemen et al., 1982).Atmospheric N deposition may lead to eutrophication of natural ecosystems and loss of biodiversity.Water management in rice and wheat fields influences the extent of N losses due to nitrification-denitrification and ammonia volatilization. Up to 50% of the applied N can be lost throughdenitrification when alternating aerobic – anaerobic conditions prevail in rice fields. A vast majorityof soils, particularly in the Indo-Gangetic plains, are relatively coarse textured and experience frequentalternating wetting and drying cycles. Data in Table 6 provides a general idea of gaseous losses ofN occurring in flooded soils. Since these data have been generated from 15N balances, it indicateslosses via ammonia volatilization as well as nitrification-denitrification. Contribution of agriculture tonitrate enrichment of water bodies and transfer of NH3 and N2O to atmosphere are discussed inlater sections.

Table 5. Nitrogen fertilizer recovery by rice and wheat from on-farm measurements (Cassman et al. 2002)

Crop Region Number of farms Average N levels, REN, %kg N ha-1 (± SD) (± SD)

Rice Asia – farmers practice 179 117±39 31±18

Asia – field specific management 179 112±28 40±18

Wheat India – unfavourable weather 23 145±31 18±11

India – favourable weather 21 123±20 49±10

Table 6. Extent of gaseous N losses computed using 15N-balance approach from flooded rice soils in India

N application rate (kg ha-1) Method and time of Gaseous N loss Referenceand source N application (% of applied N)

180, Urea Basal 34-50 Rekhi et al. (1982)

180, Urea 3 splits 17-28 Rekhi et al. (1982)

58-116, Urea, (NH4)2SO4 Basal 46-50 Katyal et al. (1985)

100, Urea Basal 58 Mohanty and Mosier (1990)


Biologically Versus Synthetically Fixed Reactive Nitrogen in Agroecosystems

Before the advent of N fertilizers, farmers used to maintain 25 to 50% of their farm under legume cropswhich regenerated soil fertility through biological fixation of atmospheric dinitrogen (N2) by legume–rhizobial symbiosis. Although the harvested seed of some pulse (edible legume) crops contained muchof the N2 fixed by the legume plants, the residues of such pulse crops still constituted a net N input tosubsequent crops. Legume-based rotations are still common in several parts of India, particularly withlarge number of resource poor farmers. As is typical for cereal crops to take up 50% or less of the Napplied as N fertilizers, some legume rotations have also shown similar low N use efficiency (Giller andCadisch, 1995; Peoples et al., 1995b; Fillery, 2001). Some times it can be attributed to mismatch betweenthe timing of nutrient supply and demand in annual cropping systems, although it is generally arguedthat legume-based agroecosystems can maintain higher levels of synchrony between N supply and cropuptake, when compared to single or dual applications of N fertilizers (Becker and Ladha, 1997; Gliessman,1998). But the data are not conclusive. Some studies showed relatively greater N synchrony in legume-based systems (Diekmann et al., 1993), but others suggest that fertilizer based systems are superior (Harriset al., 1994; Cassman et al., 1996). The potential advantage of N fertilized systems is that crops canreceive multiple top-dressings during the growing season to better match N supply with crop N demand(Cassman et al., 2002). Crews and Peoples (2004) concluded that the ecological integrity of legume-based agroecosystems is marginally greater than that of fertilizer-based systems. There is thus no markeddifference in N use efficiency between the two systems.

Sufficient data do not exist to state conclusively that legume-N is less susceptible to ammoniavolatilization than fertilizer N (Crews and Peoples, 2004). Nitrate leaching has been found to occur inboth fertilized and legume-based cropping systems (Fillery, 2001; Poss and Saragoni, 1992). However,when leguminous crops are allowed to grow throughout the fallow season, these not only fix N, but alsoscavenge soil available N. Although there are relatively few studies that have directly compared nitrateleaching in legume and fertilizer-based systems, yet limited evidence suggests that in some cases, nitrateleaching may be reduced when N is supplied by legumes compared to N fertilizers (Crews and Peoples,2004). While a few studies have carefully compared N2O fluxes between legume-based and fertilizer-based farming systems, no direct comparisons have been made of NO fluxes (Davidson and Kingerlee,1997). Little difference between legume and fertilizer-based agricultures has been reported for N2Oemissions. In a literature review of N2O emissions from 87 different agricultural soils, Bouwman (1996)reported fluxes ranging between 0 and 4 kg N ha–1 year–1 for unfertilized control plots. Fields plantedwith legumes were found to maintain N2O fluxes as low as 0–0.07 kg N ha–1 year–1 (Conrad et al., 1983).

Integrated Management of Reactive Nitrogen Contained in Organic Manures and ChemicalFertilizers

Despite the fact that organic manures contain almost all the essential plant nutrients and produce severalother non-nutrient benefits, their value was principally assessed in terms of N only (Tandon et al., 1997).Nevertheless, these studies have revealed that (1) N contribution of organic amendments was highlyvariable, unstable, and typically low and (2) organic manures/amendments should supplement and notsupplant nutrient supplies through fertilizers (Katyal et al., 2001). As a result, combined use of chemicalfertilizers and organic manures, referred to as integrated nutrient management, and has emerged as animportant component of the soil fertility management research program in India.

In general, N release from organic amendments is slow and is considered to be better synchronizedwith removal of N by crop plants. Efficient integrated nitrogen management systems ensure that fertilizerN is applied only when adequate amount of N is not being mineralized from organic components. Fertilizer


N equivalence of organic materials is thus also influenced by the manner in which fertilizer N was integratedwith organic components of the system. Bijay-Singh et al. (1997) showed that poultry manure-N wasalmost as efficient as urea-N in increasing yield and N uptake of rice. On the other hand, rice yield fromcombined application of 12 t of farmyard manure (FYM) ha–1 and 80 kg N ha–1 was equal to an applicationof 120 kg N ha–1 as fertilizer (Maskina et al. 1988). Efficiency of N added from FYM as compared withurea, ranged from 42 to 53 % in rice (Yadvinder-Singh et al., 1995).

What can be Done with Increasing Nitrogen Use in Indian Agriculture?

With a population of around 1.1 billion, a growth rate of 1.4% and an ineffective population controlpolicy, it appears difficult to reduce the population of India in the 21st century. Following the linear relation(Zheng et al., 2002) between accumulation of N in the environment derived from anthropogenic reactiveN in Asia in the past four decades (Y, Tg, N year–1) with a total population (X, billion) as Y = 22.798*X– 34.383 (R2 = 0.98, p < 0.001), it does not seem possible to mitigate N-enrichment to any great extentbecause Indian agriculture will have to produce food for its burgeoning population by greatly relying onincreasing reactive N. Galloway et al. (2002) lists three specific needs for agriculture if it has to continueto produce enough food for the masses and at the same time protect the environment from reactive-N related problems: (1) reduced use of chemical fertilizers, (2) increased efficiency of reactive N use infood production, including recycling of agricultural wastes, and (3) increased denitrification of reactiveN that cannot be recycled. The first leads to reduced production of reactive N, the second keeps reactiveN in the agroecosystem and also helps achieve the first and the third eliminates the reactive N beforeit can leak to the environment. Under Indian conditions, maximum emphasis needs to be given on increasingN use efficiency in agroecosystems, particularly in rice and wheat based cropping systems as most ofthe reactive N is applied to these crops.

Strategies based on applying N at the right amount, right time, and in the right place have alreadybeen developed and are in use. Recent literature on improving N use efficiency has emphasized on achievinggreater synchrony between crop N demand and the N supply from all sources throughout the growingseason (Abrol, 1990; Abrol et al. 1999; Cassman et al. 2002). This approach explicitly recognizes theneed to efficiently utilize both indigenous and applied N because losses of N via different mechanismsincreases in proportion to the amount of available N present in the soil at any given time. Decisionsregarding improvements in fertilizer-N use efficiency will begin at the field scale where farmers need todeal with the variability in soils, climate, and cropping patterns. As there exists a large fertilizer-N substitutionvalue of soil N, it is important to know the amount and temporal variations of the indigenous N supplyduring crop growth for determining the optimal timing and amount of fertilizer N applications. Sinceindigenous N supply is highly variable in the same field over time as well as in different fields withina given agroecological region (Cassman et al. 2002), accurate predictions are not an easy task. This highdegree of variability and very small size of the indigenously available N relative to much larger backgroundof total soil N makes the prediction of indigenous soil N supply as one the key challenges for enhancingfertilizer N-use efficiency. Optimum moisture and temperature, insect and weed management, adequatesupply of nutrients other than N and use of best cultivars all contribute to efficient uptake of availableN and greater conversion of plant N to grain yield. In other words, only a well managed crop can leadto optimum N use efficiency and profit from applied N along with least possible N losses to the environmentby maintaining plant available- N pool at the minimum size required to meet crop N requirement at eachstage of growth.

Most of the fertilizer-N is lost during the year of application. Consequently, N and crop managementmust be fine-tuned in the cropping season in which N is applied. Two broad categories of conceptsand tools have been developed to increase N use efficiency. Those in the first category include genetic


improvements and management factors that remove restrictions on crop growth and enhance cropN demand and uptake. Management options that influence the availability of soil and fertilizer-Nfor plant uptake come in the second category. These include: site specific N application rates to accountfor differences in within-field variation in soil N supply capacity (in large fields), field specific N applicationrates in small fields, remote sensing or canopy N status sensors to quantify real-time crop N status,better capabilities to predict soil N supply capacity, controlled release fertilizers and fertigation. Ladhaet al. (2005) compared different strategies to improve N use efficiency on the basis of benefit costratio and limitations. If a new technology leads to at least a small and consistent increase in cropyield with the same amount or less N applied, the resulting increase in profit is usually attractiveenough for farmers to adopt such technologies. With very high benefit cost ratio and with no limitation,use of simple and inexpensive leaf colour chart assists farmers in applying N when the plant needsit. As the use of leaf colour chart can adequately take care of N supply from all indigenous sources,it ensures significant increase in REN and reduced fertilizer N use. This tool is particularly useful forsmall to medium size farms in developing countries. Similarly, precision farming technologies basedon gadgets like optical sensors have demonstrated that variable rate N-fertilizer application has thepotential to significantly enhance N use efficiency by crops like rice and wheat. Efforts are alreadyunderway to make these technologies available to farmers but it will take some time before thesewill become farmer friendly under Indian farming conditions.

Modern N management concepts usually involve a combination of anticipatory (before planting)and responsive (during the growing season) decisions. Improved synchrony, for example, can be achievedby more accurate N prescriptions based on the projected crop N demand and the levels of mineral andorganic soil N, but also through improved rules for splitting of N applications according to phenologicalstages, by using decision aids to diagnose soil and plant N status during the growing season (models,sensors), or by using controlled-release fertilizers or inhibitors. Important prerequisites for the adoptionof advanced N management technologies are that they must be simple, provide consistent and large enoughgains in fertilizer N use efficiency, involve little extra labour and be cost-effective.

Reactive Nitrogen in Animal Agroecosystems

Animal agroecosystems produce dietary protein (milk, eggs, and edible meat) from the consumption ofproteins produced by crop agroecosystems. Depending on animal species, ration and management,between 5 % and 45 % of the N in plant protein is converted to and deposited in animal protein. Theother 55 % – 95 % is excreted via urine and feces, and can be used as nutrient source for plant production.As in crop agroecosystems, most of the reactive N that enters the animal agroecosystem is lost to theenvironment over the course of a year (Galloway et al., 2003). Cattle, sheep and pigs have the largestshare in animal manure N production. The conversion of plant N into animal N is on average moreefficient in poultry and pork production than in dairy production, which is higher than in beef and sheepproduction. Typical rates of N-use efficiency for production of human-digestible protein from feed grainsand forages on farms are about 50 % to 60 % for fish, about 40 % to 50 % for poultry, about 35%to 40% for dairy and about 15 % to 30 % for beef (Galloway et al., 2003). The efficiency of the conversionof N from animal manure, following application to land, into plant protein ranges between 0 and60 %, while the estimated global mean is about 15 %. The other 40 % – 100 % is lost to environmentvia NH3 volatilization, denitrification, leaching and run-off during storage and/or following applicationof the animal manure to land. Relative large losses occur in confined animal feeding operations, as theseoften lack the land base to utilize the N from animal manure effectively. Nitrogen conversion in animalproduction systems can be improved by manipulating composition of the animal feed and proper


management of the animal manure. Of the total N consumed by animals, about 15 % is consumed byhumans. The remaining reactive N is lost as manure and waste (Smil 2001, 2002). Coupling of cropand animal production systems, at least at a regional scale, is one way to high N use efficiency in thewhole system.

The negative growth rate was recorded in cattle population in India in recent years (16th IndianLivestock Census, 2003; 17th Indian Livestock Census, 2005) due to mechanization in agriculture andeconomic considerations. Gupta et al. (2007) calculated the bovine population in the country in 2000as more than 271 × 106 (Table 7). Total dry matter consumed by bovine in India during 2000 was ofthe order of 471 Tg. Out of 210 Tg dung produced, only around 80 Tg was used as manure; similarquantity was used for making dung cakes (Table 8). Dung cake is utilized in most of the states of India,except Himachal Pradesh, Jammu and Kashmir and North-Eastern states and is less utilized in Keralaand Delhi (Gupta et al., 2007). Manure management includes storage and treatment of manure, beforeusing it as farm manure or burning as fuel. Production of N2O from animal manure depends on digestibilityand composition of feed, species of animals and their physiology, manure management practices. Nitrousoxide emission factors and total emission from manure management in India has been discussed in asubsequent section.

Table 7. Bovine population, dry matter excretion, N2O emission factors and emission estimates from bovinemanure management in India for the year 2000 (Adapted from Gupta et al., 2007)

Category Age Dry matter excreted Population N2O emission N2O emission(kg head-1 day-1) (× 1000)† factor (mg head-1 year-1) (kg)

Dairy indigenous Adult 1.93 ± 0.06 47877 9.7 ± 1.9 465.2 ±91.8

Dairy crossbred Adult 2.35 ± 0.07 8865 8 ± 1.6 70.9 ± 14

Non-dairy cattle Below 1 year 0.79 ± 0.02 17249 3 ± 0.6 52.2 ± 10.3(indigenous) 1-3 year 1.88 ± 0.05 30758 6.5 ± 1.3 200.3 ± 39.5

Adult 2.61 ± 0.07 68345 8.9 ± 1.7 605.5 ± 119.5

Non-dairy cattle Below 1 year 0.73 ± 0.02 3290 3.3 ± 0.6 10.8 ± 2.1(crossbred) 1-2.5 year 1.57 ± 0.04 3819 7.8 ± 1.5 29.6 ± 5.8

Adult 2.14 ± 0.06 3943 10.8 ± 2.1 42.6 ± 8.4

Dairy buffaloes Adult 2.65 ± 0.08 44295 11.0 ± 2.2 485.3 ± 95.7

Non-dairy buffaloes Below 1 year 1.26 ± 0.04 14090 5.2 ± 1 73.6 ± 14.51-3 year 2.4 ± 0.07 16362 9.9 ± 2 162.4 ± 32Adult 2.83 ± 0.08 12422 11.7 ± 2.3 145.5 ± 28.7

Total 271314 2343.8 ± 462.4

†Compounded annual growth rate in bovine population between 1997 and 2003 (16th Indian Livestock Census, 2003; 17thIndian Livestock Census, 2005) was applied to the population recorded in 16th livestock census to obtain population for theyear 2000 and animals below 3-months age group were excluded, due to their negligible dry matter excretion.

Table 8. Use pattern of bovine dung produced in India during 2000 (Adapted from Gupta et al., 2007)

Type of use % of total Quantity (Tg)

Dung cake 38.4 80.5

Biogas 7.4 15.6

Rangeland 14.0 29.4

Slurry and lagoon 1.0 2.1

Others 1.0 2.1

Manure 38.2 80.2

Total 209.8


REACTIVE NITROGEN FROM USE OF FOSSIL FUELS IN INDUSTRY, TRANSPORT AND ENERGYPRODUCTION IN INDIA

Fossil fuel combustion is a major source of NOx inputs to the atmosphere. There are two broad categoriesof sources for these emissions. Thermal NOx is generated by the oxidation of diatomic nitrogen as aby-product of combustion. In the second category, fuel NOx is formed when the nitrogen contained inthe organic compounds that comprise fossil fuels is released to the atmosphere. While thermal NOx isdominant for fuels with low nitrogen content such as natural gas and petroleum distillates, fuel NOx whichaccounts for 50–90 % of the emissions associated with heavier fuels such as residual oil and coal containingbetween 0.3% and 3.0 % N by weight (Seinfeld 1986). Estimations of NOx emissions are often not subjectto direct measurement but are instead inferred from data on fuel use. The consumption of different energycarriers such as hard coal, lignite, gasoline, residual fuel oil, natural gas, is multiplied by average emissioncoefficients that are derived from field observations and/or laboratory studies (Müller 1992). This approachis useful in generating order-of-magnitude emission estimates, but is unable to account for the role ofspecific technologies in mediating the relationship between fuel use and NOx emissions. This method,however, is often the best that can be done to estimate NOx emissions in developing countries, wheredisaggregated data on the disposition of fuel consumption by end use or process are often of low qualityor are entirely lacking (Mosier et al. 2002).

Garg et al. (2006) have attempted to provide aggregated energy consumption major fuel categoriesin India during 1985-2005. These data as listed in Table 9 along with default emission factors for differentsource categories (IPCC, 1996) were used by Garg et al. (2006) as the basis for working out NOx emissionsfrom energy sector. Wherever possible India specific emission factors were used. The NOx emissions frommobile vehicles are related to the air–fuel mix, combustion temperatures and the pollution control devicesinstalled in the vehicle. Diesel vehicles emit more NOx as compared to petrol driven vehicles. NOx emissionfrom heavy-duty vehicles is significantly higher than those for cars and light commercial vehicles. Otherthan these fossil fuel combustion source categories for NOx emissions, nitric acid production is the mainnon-energy source of NOx emissions (Garg et al., 2006). Nitric acid is produced from the catalytic oxidationof ammonia and nitrogen oxides are released in the process. Emissions are estimated from the amountof nitric acid produced.

Data pertaining to NOx emissions in India as listed in Table 10 (Garg et al., 2006) reveals that around2.11 Tg NOx were emitted in 1985 and these were increasing at a rate of about 4.5% per annum between1985–2005. Coal (mainly in power generation sector) and oil combustion have almost equal shares in

Table 9. Energy consumption during 1985–2005 in India (Garg et al., 2006)

Fuel type Units 1985 1990 1995 2000 2005

Bituminous coal Tg 116.7 165.8 231.2 289.0 347.0

Lignite Tg 8.1 13.8 21.8 22.7 31.0

Coking coal Tg 36.5 47.7 51.9 51.6 56.2

Natural gas BCMa 4.2 10.9 19.1 23.3 31.0

Oil products Tg 43.3 58.6 78.8 108.8 132.0

Motor gasoline Tg 2.3 3.5 4.7 6.6 9.0

Diesel Tg 15.9 23.6 34.9 42.0 43.0

Kerosene Tg 6.2 8.4 9.9 11.3 12.6

Heavy fuel oil Tg 9.6 10.8 12.9 16.2 18.6

Sources: Synthesized and compiled from CMIE (2000, 2005), OCC (1998), INC (2004) Enerdata database; IEA (2003); BCM(Billion Cubic Meter)


total NOx emissions. Road transport sector is the predominant source of NOx emissions contributing 34%to Indian emissions in 2005. Emissions from diesel combustion in transport sector have more than doubledduring 1985–2000. Power generations followed by industry are the next largest contributors. Analysisof changing sectoral NOx emission shares during 1985–2005 indicates an increase in power sector sharefrom 18% to 30% and road transport from 25% to 33% (Garg et al., 2006). On the contrary, the emissionshare of biomass burning has declined from 28% to 15%, other industries (10–6%) and railways(6–3%). It must be noted here that absolute emissions from all these sources have increased during thisperiod. Differential growth rates result in changing emission shares.

Using the default IPCC emission factors Singh et. al. (2007) estimated that the Indian road transportsector contributed about 0.3 Tg NOx emissions in 1980 which increased to 1.1 Tg in 2000. The diesel-powered vehicles were the dominant contributors and account for about 84% of the total NOx emissionsfor the road transport sector. It could possibly be due to higher consumption of diesel in freight and passenger(mass transport) transport vehicles which are mostly powered by diesel engines.

Field burning of crop residues constitutes an important source of NOx in India. According to Guptaet al. (2004), 40 Gg of NOx were emitted in 1994 due to field burning of wheat residues in the country.Recently, Sahai et al. (2007) estimated that the field burning of wheat residue was responsible for emissionsof 33±32 Gg of NOx for the year 2000.

Recently Ohara et al. (2007) developed a new emission inventory for Asia called Regional EmissionInventory in Asia (REAS) for the period 1980–2020. REAS is the first inventory to integrate historical,present, and future emissions in Asia. Emissions were estimated on the basis of activity data at districtlevels for China, India, Japan, South Korea, and Pakistan. For the other countries, national emissionswere estimated on the basis of activity data at the national level. Emissions of NOx from fuel combustionsources and non-combustion sources as part of anthropogenic activities were estimated from transformation(power) sectors (electricity and heat production, oil refineries, manufacture of solid fuels, and other energyand transformation industries); industry sectors (including iron and steel, chemical and petrochemical,non-ferrous metals, and non-metallic minerals); transport sectors (including aviation, roads, railways, andshipping); and other (mainly domestic) sectors (including agriculture, commerce and public, and residential).Emissions were estimated as a product of the activity data, emission factors, and removal efficiency of

Table 10. NOx emissions from different sectors in India (Tg –NOx)

Source categories 1985 1990 1995 2000 2005 CAGR % (1985-2005)

Power 0.377 0.620 0.964 1.283 1.547 7.3

Road 0.520 0.670 0.985 1.380 1.696 6.1

Rail 0.120 0.101 0.100 0.110 0.132 0.5

Navigation 0.010 0.012 0.014 0.018 0.023 4.3

Aviation 0.018 0.024 0.033 0.042 0.051 5.4

Cement 0.040 0.060 0.085 0.116 0.148 6.7

Steel 0.123 0.152 0.181 0.206 0.231 3.2

Brick 0.078 0.094 0.109 0.133 0.165 3.8

Other industries 0.204 0.229 0.263 0.287 0.315 2.2

Biomass burning 0.586 0.633 0.670 0.670 0.630 0.5

Nitric acid production 0.002 0.004 0.006 0.011 0.013 9.8

Other sectors 0.030 0.040 0.046 0.049 0.051 2.7

All India (Tg NOx) 2.110 2.640 3.460 4.31 5.020 4.4

Source: Garg et al. (2006)


emission controls. Region-specific emission factors for several emission species from subdivided sourcesectors were developed from a wide range of sources and were used to estimate emissions on districtand country levels. The estimates on district and country levels were divided into a 0.5°×0.5° grid byusing index databases – population data; information on the positions of large point sources; land coverdata sets and land area data sets. On-road vehicles were classified into seven types (light-duty gasolinevehicles, heavy duty gasoline vehicles, light-duty diesel vehicles, heavy-duty diesel vehicles, gasoline buses,diesel buses, and motorcycles). Motor gasoline and diesel oil consumption was distributed to each vehicletype by using traffic volume and fuel economy data, and then the emissions were estimated by usingcountry-specific emission factors by vehicle type.

Table 11. National NOx emissions in Asian countries during 2000 (Adapted from Ohara et al., 2007)

Country NOx (kt year-1)

India 4730

China 11186

Japan 1959

South Korea 1559

Indonesia 1653

Pakistan 640

Thailand 591

All Asia 27316

Table 12. Fuel consumption (PJ) between 1980 and 2003, mean emission factors for fuel combustion in 2000and NOx emissions in 2000 by region, sector and fuel type in India and Asia (Adapted from Oharaet al., 2007)

Region Year Power plants Industry Transport Domestic Total

Coal Oil others Coal Oil others Oil others Coal Biofuel others

Fuel consumption (PJ)India 1980 902 120 18 565 525 906 472 229 323 5920 284 10263

1990 2481 150 145 1141 865 1321 996 102 464 7051 514 15229

2000 5201 325 422 874 2382 1741 1273 0 355 7866 948 21387

2003 5655 310 567 987 2470 1758 1313 0 388 8239 1088 22776

China 1980 2410 963 105 5498 1605 875 640 402 3017 4751 595 20860

1990 6046 659 193 8836 8518 1439 1145 430 4655 5788 908 32618

2000 12679 604 457 10828 4447 1991 2726 236 3055 5289 2207 44520

2003 18584 714 440 13040 5436 2689 3347 239 3102 5401 2651 55644

Asia 1980 3856 4679 1325 7537 7738 3752 4385 634 3917 15602 3563 56986

1990 10248 4086 2815 11905 9804 6130 7360 532 5670 18532 5313 82395

2000 22284 3566 5766 13751 17070 8936 12135 241 3625 19420 8697 115490

2003 29984 3217 7011 16443 19121 10083 13262 264 3707 20172 9296 132559

Mean NOx emission factors for fuel combustion in 2000

China 298.8 279.2 161.2 241.8 79.8 78.6 1017.1 241.2 95.0 82.9 110.8 246.3

Asia - other 267.0 303.1 189.8 240.7 81.2 79.7 921.1 79.7 122.9 81.4 74.1 157.3than Chinaand Japan

Regional NOx emissions in 2000 (kt year-1)

India 1543 185 81 249 228 161 1564 0 45 618 56 4730

China 3788 169 74 2839 357 156 2773 57 290 439 245 11186

Asia 6012 842 717 3695 1217 690 9169 57 361 1588 763 27316


Total emissions of NOx in Asia were 27.3 Mt in 2000 (Table 11); China at 11.2 Mt (65%) and Indiaat 4.7 Mt (17%) were high-emission countries. Japan (7%), South Korea (6%), and Indonesia (6%) alsomade relatively large contributions. Table 12 lists sectoral and fuel-type consumption, mean emission factorsand emission of NOx for India, China and Asia as worked out by Ohara et al. (2007) following REAS.On Asia basis, NOx emissions from transport oil use were the largest (34%), followed by coal use inpower plants (22%) and industrial coal use (14%). For contributions by fuel type alone, oil use (41%)was slightly greater than coal use (37%). In China, the country with the largest emissions, coal-burningpower plants were the largest emitters (34%), followed by industrial coal use and transport oil use (bothat 25%). In India, the contributions of coal-burning power plants and transport oil use were dominant(both at 33%). Additionally, domestic biofuel use was a large contributor (13%) – larger than inChina (4%).

Ohara et al. (2007) compared the Asian total NOx emissions for 2000 as estimated by REAS andother inventories and found that the REAS value (25.1 Mt) was almost the same as the IIASA one (25.8Mt), whereas the TRACE-P value (22.7 Mt) was 10% lower, and that of EDGAR (31.1 Mt) 24% higher,than the REAS value. For Indian NOx emissions (Table 13), the REAS (4.7 Mt) and IIASA (4.6 Mt) valueswere very close, whereas the TRACE-P value (4.0 Mt) was slightly lower, and the EDGAR (6.3 Mt) valuehigher, than the REAS and IIASA values.

Total emissions of NOx in Asia between 1980–2003 showed a monotonic increase with no dips.Sectoral contributions to Asian NOx emissions revealed that emissions from the power plants, industry,transport, and domestic sectors contributed 17%, 29%, 37%, and 17%, respectively, in 1980 and 33%,22%, 35%, and 10%, respectively, in 2003 (Ohara et al., 2007). Contribution of power plants almostdoubled between 1980 and 2003. Indian and other South Asian NOx emissions in 2020 were estimatedat 7.1 Mt and 2.2 Mt, respectively (Table 14) – a rapid growth in emissions (by 49% in India and 122%in other South Asia) compared with 2000 levels (Ohara et al., 2007).

Table 13. Comparison of estimates of NOx emissions in India during 1995 and 2000a (kt year-1) (Adaptedfrom Ohara et al. 2007)

Study 1995 2000

Garg et al. (2001) 3460 –

Streets et al. (2001) 4500 –

Streets et al. (2003) TRACE-P – 4047

Ohara et al. (2007) IIASA 3470 4563

Ohara et al. (2007) EDGAR 3.2 5347 6285

Ohara et al. (2007) REAS 4377 4730aexcluding emissions from open biomass burning

Table 14. Projected regional NOx emissions (kt year–1) in 2010 and 2020 (Adapted from Ohara et al. 2007)

Region 2000 2010 2020

India 4730 5900 7052

South Asia other than India 992 1496 2201

China 11186 13990 15619

Japan 1959 1837 1837

All Asia 25112 31093 36124


Studies based on in situ observations over several locations in India indicate that the rural atmosphereis significantly influenced by the urban emission of NOx by transport and mixing (Chand and Lal, 2004;Varshney and Agarwal, 1992). As India is highly heterogeneous with respect to different agroclimatic featuresand with respect to emissions from urban and rural areas, synergetic use of a chemical transport modelsand satellite observations has been attempted by Kunhikrishnan et al. (2006) for better understandingof the NOx-related chemistry over India. They examined the regional characteristics of NOx inducedchemistry over India using output from the global model, Model of Atmospheric Transport and Chemistry–Max Planck Institute for Chemistry Version (MATCH-MPIC), retrievals of the tropospheric NO2 column,and corresponding emission estimates from the Global Ozone Monitoring Experiment (GOME) instrumenton board the ERS-II satellite, including an examination of the quality of the O3 simulation with respectto available MOZAIC profiles over India. They concluded that the mean regional NOx emission strengthfor India is close to 2.5 Tg N year–1 with a seasonal maximum (~3 Tg N year–1) during April and minimum(~1.6 Tg N year–1) during winter. The changes in the O3 concentrations with respect to NOx and non-methane hydrocarbon emissions from India show that southern India is relatively more sensitive to localemissions.

ATMOSPHERIC NITRIC OXIDE (NO) AND NITROUS OXIDE (N2O)

The NO emission from Asian cultivated soils (excluding the burning of crop residues) in 1980s and 1990shas been estimated at 0.8–1.2 Tg N year–1 (Zheng et al. 2002), which accounts for 16–24% of the globaltotal ranging from 1.6 to 8.4 Tg N year–1 (Davidson and Kingerlee, 1997; Delmas et al. 1997). Usingmodeling approach, Mittal and Sharma (2007) reported NO emission per unit of electricity in India as~4.8 g kWh–1. This compares to a U.S. average 3.5 ~4.8 g kWh–1 for the year 1995. For the year 1997,total NO emissions due to thermal power generation and vehicular transport in India were estimatedas 5.3 and 4.83 Tg, respectively. According to an estimate made by Sahai et al. (2007), 15±14 Gg NOwas produced from field burning of wheat residues in India during 2000.

The global atmospheric nitrous oxide concentration increased from a pre-industrial value of about270 ppb to 319 ppb in 2005 (Fig. 6). The growth rate has been approximately constant since 1980.More than a third of all nitrous oxide emissions are anthropogenic and are primarily due to agriculture(IPCC, 2007). Bouwman (1996) compiled data on N2O emissions from 87 different agricultural soils andreported fluxes ranging between 0 and 30 kg N2O-N ha–1 per year with unfertilized control plots rangingbetween 0 and 4 kg N ha–1 per year. Fields planted in legumes have been found to maintain N2O fluxesas low as 0–0.07 kg N ha–1 per year (Conrad et al., 1983). The estimate of N2O emission from agriculturalsoils and manure management in Asia for 1990s ranged from 1.1 to 1.4 Tg N year–1, accounting for17–32% of the latest global estimates of 3.9–6.3 Tg N year–1 (IPCC, 2001). Of the total anthropogenicemissions of NOx and N2O from Asian agriculture, about 68% is due to the combined contributions ofIndia and China.

Following IPCC methodologies (IPCC, 1996; Garg and Shukla, 2002), Garg et al. (2006) estimateddirect N2O emissions from soils (including use of synthetic fertilizers), field burning of agriculture cropresidue, manure management, indirect soil emissions, fossil fuel combustion, industrial activities namelyproduction of nitric acid, and waste sector in India (Table 15). Taking 178 Gg–N2O emissions for 1994as benchmark, there has been a noticeable lowering in direct N2O emission estimates from soils, includingfrom use of synthetic fertilizers. This is mainly due to the use of India specific emission factors that arelower by almost 30% than the IPCC default values. The previous emission factors were 0.93 kg ha–1

N2O–N for all types of crop regimes. The revised emission factors used for rice–wheat systems are 0.76for rice and 0.66 kg ha–1N2O–N for wheat for urea application without any inhibitors (Pathak et al., 2004).Agriculture sector activities account for more than 80% of the total N2O emission including 60% from


use of synthetic fertilizer, about 12% each from agriculture residue burning and indirect soil emissionsand about 3% from manure management (Garg et al., 2006).

Production of N2O occurs by both nitrification and denitrification during storage of animal manures.Emission factors for N2O for solid storage of animal manure in India as worked out by Gupta et al. (2007)varied from 3 to 11.7 mg head–1 year–1for different categories of bovine with a total annual emissionestimate of about 2344 kg N2O for the country (Table 7). Indigenous cattle were responsible for higheremission due to their larger population followed by buffalo and crossbred cattle.

Using geographical information system (GIS) interfaced Asia-Pacific Integrated Model (AIM / Enduse),which employs technology share projections for estimating future N2O emissions, Garg et al. (2004) analyzedreference scenarios and concluded that agriculture sector activities will account for more than 90% ofthe total N2O emissions in India presently, including 66% from the use of synthetic fertilizers, about 10%

Table 15. N2O emissions from various source categories in India in Gg-N2O (Source: Garg et al. 2006)

Source categories 1985 1990 1995 2000 2005 Compounded annual growth rate (%)

Synthetic fertilizer use 80 94 109 129 151 3.2Field burning of agricultural residues 15 18 21 21 20 1.4Indirect soil emissions 17 19 21 25 30 2.9Manure management 4 5 6 6 8 3.9Fossil fuel combustion 7 9 12 15 19 4.9Industrial processes 6 7 9 12 16 5.0Wastes 5 6 7 8 9 2.8

Total N2O 134 158 185 217 253 3.2

Fig. 6: Atmospheric concentrations of nitrous oxide over the last 10,000 years (large panels) and since 1750 (inset panels).Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red

lines). The corresponding radiative forcings are shown on the right hand axes of the large panels. (Source IPCC, 2007).


each from field burning of agriculture residues and indirect soil emissions, and about 5% from livestockexcretions. Use of synthetic fertilizers is the single largest source of N2O emissions presently and is projectedto retain this prominence in future (Table 16). Figure 7 shows the N2O emissions in the reference scenariosfor the years 2000 and 2020. The contribution of the agriculture sector, especially due to the use of syntheticfertilizers, is the dominant source of emissions, though it varies across the states.

EMISSION OF REACTIVE NITROGEN AS AMMONIA FROM TERRESTRIAL ECOSYSTEMS

Application of fertilizers and the livestock in agriculture sector are the major contributors to NH3 emissions.The estimates of NH3 in India are, however, highly uncertain as no country specific emission factor forNH3 is available as yet. Using emission factors proposed by Asman (1992), Parashar et al. (1998) estimatedthat the fertilizers applications were responsible for emission of about 1.17 Tg NH3 during 1993-94. Outof all the fertilizers, the urea application is responsible for more than 90 % of the total contribution due

2000 2020

0

750

1500

2250

3000

3750

4500

5250

>=6000

N2O ‘tons

Fig. 7: N2O emissions in India in the reference scenarios 2000 and 2020 (Source: Garg et al. 2004)

Table 16. N2O emission projections for India under the reference scenario

Source (Gg) 2000 2010 2020 2030

Coal combustion 9.9 16.8 24.0 28.0

Oil product combustion 2.0 3.6 6.4 10.0

Field burning of agricultural residue 33.9 41.5 42.6 33.4

Biological nitrogen fixation 5.6 6.6 7.8 9.1

Natural gas combustion 0 0 0 0

Synthetic fertilizer use 206.1 368.4 524.9 626.8

Livestock 12.2 14.1 16.3 18.8

Industrial processes 12.1 23.0 31.0 38.0

Indirect emissions 26.0 30.7 36.2 42.6

Total N2O (Gg) 307.8 504.6 689.0 806.7


to fertilizers. Loss of N via ammonia volatilization can be substantial when urea is top dressed. Placementof urea on the wet surface of alkaline soils promotes ammonia volatilization. If applied on the wet soilsurface following irrigation, as much as 42% of the applied 15N was lost due to volatilization (Katyalet al., 1987). However, deep placement of urea due to its application before irrigation and resultant reductionin losses of applied 15N from 42 to 15 % is also demonstrated from the work of Katyal et al. (1987).

Ammonia volatilization losses of reactive N fixed by legumes or applied through fertilizer N canbe substantial, especially in regions that are irrigated and/or have alkaline soils. Ferm (1998) observedthat about half of the ammonia that is volatilized is deposited in downwind ecosystems within a 50 kmradius, while the other half is deposited over a much broader region. Losses of ammonia following fertilizerapplications to upland and lowland cropping systems can range from ~0 to >50%, while losses fromflooded rice can reach as high as 80% (Peoples et al., 1995a). Fertilizer placement, the timing of application,soil temperature and fertilizer type determine loss rates (Peoples et al., 1995a). Ammonia volatilizationfrom legume residues may be high when they are left on the soil surface, but the losses do not appearto match those measured in some fertilized systems.

The contribution of livestock have been estimated to be 1.43 Tg of NH3 during 1993-94 (Parasharet. al. 1998). Out of these emissions, the cattle have been estimated to have the largest contributionamounting to 1.05 Tg followed by buffaloes which have been estimated to contribute about 0.28 TgNH3. The other categories of livestock like pigs, poultry, horses and sheep had very small contributionsin the total national NH3 emissions. These emission estimates were based on the emission factors proposedby Asman (1992) were developed using the feed intake ratios of West European cattle and may not trulyrepresent Indian conditions where the feed intake ratios are generally low.

Based on the available data from different stations in India, Kulshrestha et al. (2005) conductedprecipitation monitoring studies to work out regional patterns. The lowest NH4

+ median concentrationsof 9 μeq l–1 in the precipitation was observed over rural areas whereas a value of 14 μeq l–1 was recordedfor sub-urban areas. The urban areas precipitation showed the highest NH4

+ median concentration of22 μeq l–1; the industrial areas recorded a median value of 18 μeq l–1. The median depositional fluxesof NH4

+ species over rural, suburban, urban and industrial areas were estimated to be 10, 13, 18, 26μeq m2 yr–1, respectively (Kulshrestha et al., 2005). Although urban areas show high depositional fluxof NH4

+, values for rural areas are also substantially high and should contribute significant amount ofN to agricultural soils. However, no quantitative estimates are yet available for Indian conditions.

According to estimates made by Zheng et al. (2002), reactive N in Asia was transferred to theatmosphere by NH3 volatilization at a rate of ~ 4.6 Tg N year–1 in 1961 which increased to~ 13.8 Tg N year–1 in 2000. It is expected to reach ~ 18.9 Tg N year–1 in the next three decades. China’scontribution increased from ~ 25% in 1961 to ~ 39% in 2000, while India’s contribution decreasedfrom ~ 41% in 1961 to ~ 29% in 2000. In the next three decades, however, the contribution of Chinais expected to decrease to ~ 35% and that of India is anticipated to remain at ~ 29%. The NH3released to the atmosphere is redeposited to downwind terrestrial lands at a rate ranging from3.8 Tg N year–1 in 1961 to 15.7 Tg N year–1 in 2030, while the deposition to coastal waters stands ata rate of 0.8–3.4 Tg N year–1 over 1961–2030. As per estimates given by Zheng et al. (2002) human-excreted N, the temporal variation in livestock-excreted N is an indicator of the growth of animal husbandryin Asia. As Figure 8 shows, livestock production developed very rapidly in the 1980s–1990s. But itsdevelopment rate in the coming decades is expected to be slower and almost equal to that of1960s–1970s.


NITRATE-NITROGEN IN GROUNDWATER BODIES

Nitrate-N levels in relatively pollution free regions of world such as high altitude lakes and rivers andsnow clad mountains in central Himalayas is about 0.11 mg N l–1 (Sarin et al., 1992). According to Agrawalet al. (1999), water in a relatively pure system contains less than 0.22 mg N l–1 and concentrations higherthan this reflect anthropogenic or geological contributions. In oceans, which are the ultimate sink forterrestrial water, the average nitrate-N levels are 0.15 mg N l–1 (Mason and Moore, 1985). The UnitedStates Environmental Protection Agency (EPA) considers 3 mg NO3-N l–1as the level beyond which humanactivities may be taken as contributing nitrogenous compounds to the water bodies (Anonymous, 1987).The World health Organization (WHO) has recommended the limit of 10 mg NO3–N l–1 for drinkingwater which is equivalent to about 45 mg NO3 l–1 and it has also been accepted in India by the IndianCouncil of Medical Research.

Although studies have been performed attempting to link nitrate consumption to various illnesses,only methaemoglobinemia, (infant cyanosis or blue-baby syndrome) has been proven to result fromingestion of water containing nitrate concentrations more than 10 mg NO3–N l–1 (Kross, 1993). Methaemoglobinis probably formed in the intestinal tract of an infant when bacteria convert the nitrate ion to nitrite ion(Comly, 1987). One nitrite molecule then reacts with two molecules of hemoglobin to form methaemoglobin.This altered form of blood protein prevents the blood cells from absorbing oxygen which leads to slowsuffocation of the infant which may lead to death (Gustafson, 1993). An epidemiological investigationundertaken to assess the prevalence of methaemoglobinemia in areas with high nitrate concentrationdrinking water in Rajasthan in India revealed severe methaemoglobinemia (7%–27% of Hb) in all agegroups, especially in the age group of less than one year (Gupta et al., 2000). Many studies have beenperformed attempting to link stomach and gastrointestinal cancer to nitrate intake. Medical scientists claimthat nitrate represents a potential risk because of nitrosation reactions which, with appropriate substratespresent, form N-nitroso compounds which are strongly carcinogenic in animals (Forman, 1985). However,

Fig. 8: Livestock- and human-excreted nitrogen and its ammonia volatilization in Asia (Source: Zheng et al. 2002)


even at exposure to levels of 111mg l–1 there were no adverse conditions in infants except formethaemoglobinemia (Gustafson, 1993). Recurrent stomatitis has also been found to be associated withnitrates in drinking water (Gupta et al., 1999).

Adverse effects of nitrates in drinking water on animal health include methemoglobinemia in ruminantsand severe gastritis in monogastric animals, intestinal disorders in pigs, pregnancy related disorders inrats, depression, muscle tremors and incoordination in goats, loss of body weight and reduced waterconsumption in chickens, sexual disorders in sheep and hyperthyroid in foals (Prakasa Rao and Puttanna,2000).

Extent of Nitrate Pollution of Groundwater Bodies in India

An appraisal of risk of nitrate pollution of ground water in different parts of India can be made by consideringtogether the fertilizer N use per unit area and extent of ground water development for irrigation purposes.Excess nutrients in irrigation return flow, if not properly drained off, gradually infiltrate into aquifers. Usingthe data generated by reconnaissance of nitrate content in shallow ground waters by Central GroundWater Board (Handa, 1986), Agrawal (1999) categorized different states with respect to potential hazardof nitrate pollution of ground waters (Table 17). With the highest ground water development, averagenitrate content in ground water and average fertilizer N use, the states of Punjab and Haryana have beenplaced in the high risk zone. According to Agrawal (1999), irrigation without artificial drainage in thepoorly drained flat plains of Punjab and Haryana, comprising of a thick pile of unconsolidated andpermeable Late Quaternary-Holocene alluvial sediments (Lunkad, 1988), increases the nitrate pollutionhazard compared to that in the freely drained regions of northern and northeastern states and peninsularplateau in the southern part of the country. Agriculture is not intensive in northern and northeasternstates as reflected in the meager consumption of nitrogenous fertilizers and negligible ground water use.The situation in the peninsular states is in between the two extremes. Reports of ground water enrichmentwith nitrate-N from different parts of the country are summarized below.

Northwestern India: Depending upon availability of irrigation water, the coarse textured soils in thenorthwestern India are used for raising wheat as well as wetland rice. In this region there hardly occursany leaching of nitrate-N beyond the 2 m deep rooting zone of wheat crop (Katyal et al. 1987). On theother hand, rice grown in summer receives around 150 cm irrigation besides 33 cm of average rainfall.Under these conditions a large part of applied N is lost as nitrate via leaching to ground water. Interestingly,due to high percolation rates, soil under rice experiences alternating aerobic-anaerobic cycles that facilitate

Table 17. Risk of ground water nitrate pollution in different parts of India

Risk zone Average fertilizer N Average NO3 in Ground waterconsumption (kg ha-1) ground water development Region (states)

(mg l-1) (% of totalavailable in 1990)

Little or no risk 2 6-8 <2 Jammu and Kashmir, northeasternstates

Low risk 4-11 8-45 5-22 Himachal Pradesh, MadhyaPradesh, Orissa, Maharashtra

Moderate risk 14-53 13-50 16-40 Uttar Pradesh, Uttranchal, Bihar,Jharkhand, West Bengal, AndhraPradesh, Gujarat

High Risk 118-163 55-100 70-100 Punjab, Haryana

Source: Handa (1986), Agrawal (1999)


production of nitrate unlike in ideal rice soils. Thus as described by Bijay-Singh et al. (2007) in detail,nitrate N content in the ground water in Punjab have been consistently increasing since 1975 when firstsampling was made (Table 18). A significant correlation (r = 0.51*) was found to exist between the amountof fertilizer N applied per unit area per year and nitrate N concentration of well water in September 1975.Multiple correlation between well water nitrate N content and amount of fertilizer N applied in the vicinityof the wells and depth to water-table was 0.53** in September and 0.39* in June 1975, suggesting therebythat fertilizers may significantly increase nitrate N levels in the ground water in Punjab. As shown inTable 18, the geometric mean of nitrate N content registered an increase from 0.42 to 2.29 mg l–1 during1975 to 1988.

In 1992, ground water samples collected from 21 to 38 m deep tube wells located in cultivatedfields in different blocks of Punjab (fertilizer N use varying from 151 kg N ha–1 to 258 kg N ha–1) recordedgeometric mean nitrate N concentration of 3.62 mg l–1 (Table 19). Respectively, 78 and 22 % samplescontained less than 5 and 5–10 mg NO3

––N l–1 (Bajwa et al., 1993). Higher nitrate N concentrationsin ground water were observed in areas under rice, maize and orchards. In contrast to cultivated area,mean NO3

––N concentration in 367 water samples collected from 9 to 18 m deep hand pumps locatedin village habitations worked out to be 5.72 mg l–1 with 64 and 2 % samples containing 5–10 and >10mg NO3

––N l–1. In ground water samples collected from hand pumps located near animal feedlots ordairy farms representing a concentrated source of animal wastes in the outskirts of villages, mean NO3

–

–N concentration was observed to be 4.73+2.24 mg l–1. In 1999, several samples of water drawn fromshallow hand pumps contained nitrate-N levels much above the WHO limit of 10 mg N l–1 (Table 20).

Problem of ground water pollution by nitrates does not normally arise in areas where wetland riceis grown on fine textured ideal rice soils because nitrate is not normally formed under flooded conditions.Nitrate formed when soil is allowed to drain/dry may be promptly converted to nitrous oxide via

Table 18. Nitrate concentration (mg NO3-N l -1) in water samples from shallow wells (4 to 10 m deep) locatedin agricultural land in Ludhiana district in Punjab during 1975 to 1988

1975 1982 1988Jun Sep Jun Sep Nov / Dec

Number of observations 46 33 26 26 28

Range (mg NO3– – N1–1 ) 0.04-6.15 0.05-7.90 0.35-10.11 0.23-15.17 0.31-13.30

Geometric mean 0.42 0.42 1.48 2.13 2.29

(mg NO3– – N1–1 )

Correlation coefficient NS 0.51 NS 0.51 0.59(r) fertilizer Napplied vs NO3

N inwell water

Significant at 5% level of significance

Source: Bijay-Singh et al. (1995)

*Table 19. Nitrate concentration in water samples from tube wells in cultivated areas, hand pumps in villagehabitations and beneath feedlots in rural areas in the Punjab

Type of well Number mg NO3-N l-1 Per cent samples having

of samples Mean Range <5 mg l -1 5-10 mg l -1 >10 mg l -1

Tube wells 236 3.62+1.52 1.00 – 6.72 78 72 0Hand pumps 367 5.72+2.09 1.00 – 11.28 32 66 2Feed lots 45 4.73+2.24 1.24 – 10.44 47 51 2

Source: Bajwa et al. (1993)


denitrification. This is particularly true in case of typical or ideal rice soils, which possess very low percolationrates after these are puddled.

Malik (2000) anlaysed data on nitrate content of ground water samples collected by the Punjaband Haryana State Ground Water Boards. The number of observation wells in Punjab was 460 (including72 pizometers) while that in Haryana it was 534 (including 164 pizometers). The results pertaining tonitrate content of water samples in the two states are presented in Table 21. More than 33 % of the watersamples in Punjab and Haryana had nitrate level above the desired limit for drinking water standards.In about 17 % of the samples, the nitrate-N level exceeded 22 mg l–1. Very high nitrate content of groundwater samples suggests that sources other than fertilizers can substantially contribute nitrates to groundwater.

Delhi: In many national capital sub-regions, ground water is severely polluted by nitrate. Most of theseregions are under agricultural land use. As low as 4.4 mg N l–1 to abnormally high levels (22.2–228.8 mg N l–1) of nitrate in the ground water have been found at different places in the districts ofRohtak, Sonepat, Faridabad and Gurgaon sub-region (Datta, 2005). Ground water of the national capital

Table 21. Nitrate concentration in ground waters of Punjab and Haryana

Nitrate concentration (mg NO3-N l -1) Number of samples Average nitrate level (mg NO3-N l -1)

Punjab

0 - 10 328 (69.8) 3.2

10 -22 71 (15.1) 14.8

>22 71 (15.1) 53.1

Total 470 (100.0) 12.5

Haryana

0 - 10 222 (63.1) 3.4

10 -22 62 (17.6) 15.2

>22 68 (19.3) 63.0

Total 352 (100.0) 19.0

Punjab and Haryana

0 - 10 550 (66.9) 3.3

10 -22 133 (16.2) 15.0

>22 139 (16.9) 58.0

Total 822 (100.0) 14.4

Source: Malik (2000)

Table 20. Nitrate-N content (mg N l–1) in tube wells and hand pumps located in agricultural land in the fourblocks of Ludhiana district in Punjab in July 1999

Block Tubewells Hand pumpsRange Mean Range Mean

High Fertilizer UseJagraon 2.46–16.16 6.49 3.57–49.74 12.60Samrala 1.44–8.73 4.06 0.92-29.58 12.40

Low Fertilizer UsePakhowal 1.67–4.41 2.82 2.95–13.19 6.75Dehlon 1.32–9.25 4.29 0.15–20.64 8.67

Mean values of nitrate-N in 1992 were: Tube wells = 3.62+1.52 (n = 236),Hand pumps = 5.72 + 2.09 (n = 367)Source: Bijay Singh et al. (1995), Roopna Kaur (2000)


territory Delhi shows wide range in nitrate (2.2–355.5 mg N l–1) content. In 2003, nitrate levels in Delhiground water range from <0.22–30 mg N l–1 in Alipur Block; <0.22–35.3 mg N l–1 in Kanjhawala Block;0.44–7.11 mg N l–1 in City Block; 0.44–159.1 mg N l–1 in Najafgarh Block; 4.22–67.3 mg N l–1 in MehrauliBlock and 0.22–15.3 mg N l–1 in Shahdara Block. Large part of the area to the west, having very littlerecharge from rainfall, is severely affected by nitrate pollution of ground water (Datta et al., 1997).

Domestic wastewater effluents in Delhi exhibit nitrate-N concentration ranging from 4 to6.2 mg N l–1, which may be formed during aerobic treatment may also contribute to nitrate pollutionof ground water. However, lack of correlation between nitrate and chloride content reported by Dattaand Tyagi (1996) indicates that nitrate contribution from sewage is not significant in the whole area, exceptfor some specific locations. Ground water samples from the Indian Agricultural Research Institute farmarea showed non-uniform distribution of nitrate-N contents in most of the wells in 1990, 1991, 1995,2000, 2002 and 2003 (Datta, 2005). Analyses of soil cores indicated downward movement of two differentnitrate peaks up to 1.8 m and 5.8 m depth below ground level. This suggests that nitrate-N is movingdown in pulses. The relationship between NO3 and ä18O also suggests that the ground water in Delhioriginates from two or more isotopically distinct, non-point sources which vary spatially as well astemporarily, due to different degrees of evaporation/recharge (Datta et al., 1996, 1997) and differentamounts of fertilizer N applied.

Uttar Pradesh and Bihar: The range of concentration of nitrate-N in ground waters around Lucknowis 10–130 mg l–1 (Sehgal et al., 1989). Similarly in Barauni (Bihar), Mishra et al. (2000) has reportednitrate levels in ground water samples higher than the maximum permissible limit of 10 mg l–1. About7500 km2 of the upper Yamuna basin has been classified as an area sensitive to nutrient and contaminantleaching (Narula et al., 2003).

Maharashtra: The studies carried out by the Central Ground Water Board in the state of Maharashtrarevealed that out of 688 samples, 75 % of the samples had nitrate levels below the critical limit, 14 %have nitrate levels above 22.2 mg N l–1. While the districts of Bhandara, Nagpur and Pune showed nitrateconcentrations of above 10 mg N l–1, Jalna district had the highest percentage of samples (55.56 %)with nitrate concentrations above the permissible limits. Districts like Akola, Amravati, Chandrapur,Sholapur, Wardha, Yavatmal have nitrate concentrations above 22.2 mg N l–1. In studies carried out byDeshpande et al. (1999), ample evidence for nitrate pollution of ground water in Aurangabad districtof Maharashtra has been obtained.

South India: A study of ground water quality in Karnataka during 2000–2001 indicated 37% of habitations(numbering 20,929) are facing water quality problems and nitrate was a problem in 4,077 habitations(Nagaraj and Chandrashekaran, 2005). In the extensive GIS based survey based on 154,491 samples,nitrate-N content ranged from 22.4 to 1347.5 mg N l–1. A large number of villages were found to beaffected by high nitrate content in drinking water and pose a serious health problem. The relative numberof villages affected is given in parenthesis for some of the worst affected districts: Tumkur (35%), Mysore(20%), Kolar (21%), Raichur (10%), Mandya (5%), Devanagere (15%), Chamarajanagara (14%), Chitradurga(15%). These data suggest the presence of nitrate bearing rocks in geological formations as in some partsof Haryana. About 48% of the bore well waters of Mysore city contained more than 10 mg N l–1 of nitrate(Nagaraju and Sastri, 1999).

In Andhra Pradesh, wherever fertilizer applications are high, there is ample evidence of pollutionof ground waters by nitrate-N (Srinivasarao, 1998). Even in semi-arid regions of Deccan plateau nitrateleaching was prevalent (Patra and Rego, 1997). In Palar and Cheyyar river basin in Tamil Nadu, spatial


and seasonal variations have been analysed and relationship has been found between agricultural activitiesand nutrient chemistry of well water (Rajmohan and Elango, 2005). Nitrate content, however, was foundto be within WHO drinking water limits. In Chennai, nitrate-N levels in ground waters have been reportedin the range of 3 to 226 mg N l–1 (Rangarajan et al., 1996). Ground water samples in Swaminathapuram,Dindgal district, Tamil Nadu have been found to contain 1.4–3.8 mg N l–1 nitrate (Thirumathal andShivakumar, 2003).

Sources of Nitrates in Groundwater other than Fertilizers

Although there has been a concurrent rise in fertilizer usage with nitrate-N concentration in water, particularlywhere irrigation is practiced, there exist several other sources of nitrate-N, namely sewage effluent, animalexcreta, natural soil nitrate and decomposition of soil organic matter. In many regions, natural depositsof nitrate may constitute a major source for nitrate pollution of ground water. For example, in selectedlocations in Punjab, Haryana and western Uttar Pradesh, nitrate-N concentration in well water sampleswas several folds higher than the upper safe limit (Table 22).

Given that there are no major geological deposits in the central Punjab where fertilizer N applicationrates are the highest in the state, area and major water polluting industries are few, major source of nitratein ground water could either be sewage and animal wastes and/or agricultural chemicals – particularlyN fertilizers. The area is densely populated and raw or inadequately treated sewage is either dischargedinto irrigation channels or quite often discharged into pits or depressions from where the pollutants couldpercolate down into the ground water. The region also has a high density of cattle population. A closescrutiny of the available data revealed that there is no discernible pattern of distribution of nitrates inground waters of Punjab and Haryana (Malik, 2000). At some places where high nitrate levels in groundwater have been detected, there is a sharp decrease in nitrate-N concentration a short distance awayand vice versa. Such sudden changes in nitrate levels in ground water indicate that there is no regularpattern of nitrate distribution and pollution is localized. Thus, sewage disposal along with leaching offertilizer N are contributing to the nitrate pollution of the ground water in the Punjab. The extent ofcontribution of each source is, however, difficult to evaluate.

In a study undertaken by National Environmental Engineering Research Institute (Bulusu and Pande,1990), 1290 out of 4696 (27 %) ground water samples from selected districts in 17 states in India (excludingnortheastern states) contained more than 10 mg N l–1, the WHO upper limit. High nitrate levels in 73%samples from Nagpur metropolitan should be due to urban sewage and industrial sources. Similarly highnitrate-N content (10 to >133.3 mg l–1) in shallow and deep tube wells due to seepage from industrialeffluents and urban sewage has been reported from around Jodhpur city in Rajasthan (Mathur andRanganathan, 1990) and Lucknow in Uttar Pradesh (Singh et al., 1991).

Table 22. Nitrate content of well waters in Uttar Pradesh, Haryana and Punjab

State District mg NO3--N l -1 State District mg NO3

--N l -1 in well

in well water water

Uttar Pradesh Aligarh 61 Haryana Mahendragarh 296

Meerut 157 Ambala 223

Agra 54 Punjab Hisar 95

Bathinda 128

Sangrur 98

Source: Handa (1987)


NITROGEN IN RIVERS, COASTAL ECOSYSTEMS AND OCEANS

In coastal ecosystems, such as in estuaries and shallow embayments, sediments play a key role in thecycling of nutrients to and from the water column. These coastal areas are important because of theirrole as transient zones between land and sea in their capacity of retaining nutrients; they also harbora great variety of benthic primary producers, such as sea grasses, macroalgal mats and microphytobenthiccommunities, which live in the sediment. Reactive N in coastal ecosystems is generally received throughriverine and groundwater inputs. In some cases direct atmospheric deposition inputs from the ocean canalso be important. These inputs have increased several-fold as a consequence of human activities. Becauseof the dynamic nature of coastal ecosystems, there is limited potential for reactive N accumulation (Gallowayet al., 2003). Due to high rates of denitrification (mostly as N2) the reactive N reaching coastal regionsis mostly converted to N2 before its transport to the open ocean. With coastal systems acting as reactiveN sinks, atmospheric deposition becomes a potentially important source of reactive N for the open ocean.Although reactive N has a short residence time in coastal ecosystems, it can still have a profound impacton the coastal ecosystem because primary production in most coastal rivers, bays, and seas of the temperatezone is limited by reactive N supplies (Vitousek and Howarth 1991, Nixon et al. 1996). Greater reactiveN inputs lead to increased growth of algae.

In the Asian nitrogen cycle case study conducted by Zheng et al. (2002), the riverine discharge ofdissolved inorganic nitrogen derived from anthropogenic reactive N in Asia into the Pacific and IndianOceans was estimated at ~ 2.6 Tg N year–1 in 1961, ~ 6.8 Tg N year–1 in 2000 and ~ 9.6 TgN year–1 in 2030. The discharge rates around 2000 accounted for approximately 34% of the global totalof ~ 20 Tg N year–1 (Seitzinger and Kroeze, 1998). The estimated rate of this study for mid 1990s(~ 6.4 Tg N year–1) is lower than that (~ 9 Tg N yr–1) presented by Seitzinger and Kroeze (1998). National-level analysis showed that ~ 66% of the Asian total dissolved inorganic nitrogen discharge by rivers occursin China and India. According to Caraco and Cole (1999), reactive N is being exported in the form ofnitrates out of the watershed of the Ganges, Yangtze, Huanghe and Mekong at a rate of 601, 495, 276and 144 kg N year–1 km–2, respectively. Nearly 2,236 Mg of nitrogen is discharged into Mahim Bay aloneevery year from various sources (Sen Gupta et al. 1989). This may even lead to phytoplankton bloomsin coastal areas and carbon and energy become concentrated at lower tropic levels with potentially significanteffects for ecosystem structure and function. These marine regions where phytoplankton blooms occurare located adjacent to rapidly developing agricultural areas in South Asia (Beman et al., 2005).

Nearly all the reactive N that is injected into surface waters is denitrified along the stream–river–estuary–ocean continuum (Galloway et al., 2003). While most of this reactive N is converted to N2, afraction is converted to N2O and NO. Model estimates suggest that rivers, estuaries, and continental shelvesaccount for approximately 30% of the total global anthropogenic N2O emissions (Seitzinger et al., 2000).In a recent study in the Andaman Islands (Barnes et al., 2006), denitrification rates as reported inTable 23 were generally up to 3 orders of magnitude lower than in typical temperate settings (Barnes

Table 23. Denitrification rates in four Indian mangroves

Area Rate of denitrification (mmol m-2 h-1)

Andaman Islands, India 7.6

Muthupet, South India 17.4

Pichavaram, South India 23.0

Sunderbans, India 11.2

Source: Barnes et al. (2006)


Table 24. Nitrogen budget of Arabian Sea (north of 6° N)

Tg N year-1

SourcesAtmospheric dry and wet deposition of NO3 and NH4 1.6

Pelagic N fixation 3.3

Input from marginal seas (red Sea, Persian Gulf) 1.1a

Dissolve inorganic N input from rivers 1.2b

Northward transport 38

SinksPelagic denitrification 33

Sedimentary denitrification 6.8

N sedimentation >0.22

N2O loss to the atmosphere 0.25

NH3 loss to the atmosphere 0.05c

Ó Sources – Ó Sinks 4.9

Source: Bange et al. (2000)

and Owens, 1998), consistent with low concentrations of NO3– in the mangrove surrounding waters. The

N2O emission fluxes were relatively high (0.5–10.4 ìmol m–2 d–1) and in good agreement with other studiesof mangroves N2O emissions (Bauza et al., 2002; Corredor et al., 1999). The studies carried out by Corredoret al. (1999) and Bauza et al. (2002) implied that nitrification was the major N2O source; the estimatedN2O emissions generally far exceed the reported maximum denitrification N2O yield of 6% (Nevison andHolland, 1997). Given that the energy yield for organic C oxidation by reduction of N2O to N2 is high(second only to that of aerobic respiration) in most mangrove sediments, denitrification is likely to bea sink for N2O rather than a source (Amritha et al., 2007).

The Arabian Sea is vulnerable to potential environmental and climatic changes arising from humanactivities including rapid population growth, intensification of agricultural activities including large increasesin the consumption of nitrogen fertilizers, industrialization, and urbanization of coastal zones in the majorlittoral countries (India, Pakistan and Iran) (Bange et al., 2005). Bange et al. (2000) estimate that~1.2 Tg of N in the dissolved inorganic form is added annually to the Arabian Sea (Table 24); this inputrepresents about 29% of the total fixed-N in annual river runoff from South Asia (4.2 Tg inorganic N;Seitzinger et al., 2002). Due to lack of systematic, long-term investigations of biogeochemical cycles, itis difficult to evaluate the extent to which human activities have affected the biogeochemical processesof the Arabian Sea (Bange et al. 2005). The most convincing evidence in this regard comes from theeastern Arabian Sea where coastal waters seem to have undergone a dramatic change during the lastfew years indicated by the shift from seasonally low-O2 conditions (Banse, 1959; Carruthers et al., 1959)to suboxic and even anoxic conditions (Naqvi et al., 2000). The most intriguing aspect of N cycling inthe coastal O2-deficient zone is the enormous accumulation of N2O. It seems to occur in waters experiencingintense and relatively short-lived denitrification, a pattern that distinguishes the coastal suboxic systemfrom the one located offshore (Naqvi et al., 2005). Depletion of O2 in coastal waters will not only leadto increased emissions of greenhouse gases such as N2O but will also change the food web structureand fisheries (Malakoff, 1998; Wu, 2002). Annual input of N by wet and dry aerosol deposition is estimatedto be about 1.6 Tg N and represents a minor source of N for the Arabian Sea (Bange et al., 2000).However, as is the case for land runoff, the atmospheric inputs of N through both dry and wet depositionare expected to increase steadily. During the north-eastern monsoon, air masses from the Indian subcontinent


are transported to the central Arabian Sea where the NH4+ and NO3

– containing aerosols that originatefrom agriculture and combustion processes fertilize the N-depleted surface waters. Bange et al. (2000)estimated that up to 17% of the N demand in the surface layer of the central Arabian Sea during thenorth-eastern monsoon is being met by the deposition of nitrogenous aerosols. Assuming that the amountof N aerosols will increase in the future, this source can have impacts on both biogeochemical cyclingand ecosystem structure.

CHALLENGES AND OPTIONS FOR MITIGATION OF ENVIRONMENTALLY IMPORTANTREACTIVE NITROGEN, RESEARCH AND PLANNING

The International Nitrogen Initiative – a global effort to optimize nitrogen’s beneficial role in sustainablefood production and to minimize nitrogen’s effect on human health and the environment aims at pursuinga three stage strategy that involves assessing knowledge on N flows and associated problems, developingregion specific solutions and implementing scientific, engineering and policy tools. The development ofpolicies to control unwanted reactive N release is not easy because the largest amount of anthropogenicallyfixed reactive N is related to food and energy production and reactive N species can be transported greatdistances in the atmosphere and in aquatic systems. Reactive N emissions from fuel combustion (NOx)can be reduced by following strict policies but reducing the introduction of new reactive N in food productionseems to be very difficult in countries like India having burgeoning populations. Food production stillneeds to be increased to raise nutritional levels or to keep up with population growth, which may requireincreased use of N fertilizers. Nevertheless, policies are to be implemented and enforced at the nationalor provincial/state levels although N cycling occurs at regional and global scales. Multinational efforts tocontrol N loss to the environment are surely needed, but these efforts will require commitments fromindividual countries and the policy-makers within those countries (Mosier et al. 2002).

Fertilizer nitrogen use has been an essential component of the Green Revolution that dramaticallyincreased food production in India during the period between 1960 and 1980. Fertilizer use will continueto grow as food production does, in order to keep pace with a still-rapidly increasing human population.Use of N for agriculture, whether in the form of synthetic or organic fertilizer, is not substitutable, andstraightforward technological changes are unlikely to provide a replacement. Plants will always requirea relatively large amount of N to carry out their photosynthetic processes, and one key to maintainingadequate food supplies will be supplying plants with adequate N (Matson et al. 1997). As a matter offact, the loss of fertility of agricultural soils as a result of depletion of nitrogen can lead to reduced foodproduction resulting in a catastrophe no less serious than from other forms of environmental degradation.Thus benefits of fertilizer use to agricultural production in India far outweigh the detrimental effects onthe environment. Use of increasing amounts of reactive N in the form of fertilizers in Indian agricultureand the proper management of fertilizer N will remain at the forefront of issues to improve the reactiveN balance over both the short- and long-term. To achieve the tripartite goal of food security, agriculturalprofitability and environmental quality in a country like India, improving N use efficiency in agriculturewill have to be the top priority. Since practices that result in high fertilizer nitrogen use efficiency provideenvironmental protection, high crop yields and profits, increasing fertilizer use efficiency should be amongthe highest research priorities. Holistic approach to farming systems will have to be adopted and it shouldbe based on soil characteristics, climatic constraints, moisture availability and the management skills ofthe individual farmers. Other important research areas that can help improve fertilizer use efficiency areintegrated management of organic, biological and mineral nutrient sources, identification of best managementpractices and fertilizers for specific conditions. Some other ways to increase the efficiency of reactive Nuse in food production and thus decrease the reactive N creation rate can be to increase recycling ofreactive N within agroecosystems (Smil 2002), increase use of cultivation- induced BNF (Roy et al. 2002),


provide incentives to reduce over fertilization, and redistribute reactive N from areas with high reactiveN production to areas where there is a need for reactive N for food production (Galloway et al., 2003).

Innovative fertilizer management has to integrate both preventive and field specific corrective Nmanagement strategies to increase the profitability in irrigated rice and wheat systems and to ensure thatthere exists synchrony between crop N demand and supply of mineral N from soil reserves and fertilizerinputs. It will lead to maintenance of plant available N pool at the minimum size required to meet cropN requirements at each growth stage with little vulnerability to loss of N to environment. There is significantpotential to increase N use efficiency at the farm level because concepts and tools needed to achieveit are already available. However, new technologies need to be cost effective and user-friendly so thatthese become attractive to farmers. Collaborative effort of agronomists, soil scientists, agricultural economists,sociologists, ecologists and politicians can help agriculture make substantial contribution to reduce thereactive N load.

The need to identify relative contribution of fertilizer N to environmental problems on a regionalbasis is very important. For example, in some regions, inputs other than fertilizers, such as animal wastes,may be main polluter. To work out precisely the contribution of fertilizers to nitrate pollution of groundwater, there is a need to monitor periodically nitrate-N status of ground water at different depths andmonitoring the changes every 2-3 years. It will also help distinguish different sources of nitrate-N andtheir contributions to ground water pollution. Comprehensive models which can predict the amount ofN reaching the natural water bodies under the given set of soil, crop and climatic conditions are neededto be developed. Calculation of residence time of nitrate-N in the soil profile after it escapes the rootzone will enable prediction of time trends for nitrate-N levels in ground water bodies. Methods of controllingleaching losses of nitrates from agricultural fields through better cropping practices, better fertilizermanagement and better irrigation management need to be further refined. Non-availability of comprehensivedata sets in India is a major problem in detection and prevention of nitrate pollution of ground water.Central Pollution Control Board and Central Ground Water Board of India are engaged in monitoringof water quality in the country but still the extent and distribution of pollutants across the country hasnot been quantified. Therefore, it is essential to establish ground water-monitoring stations through outthe country. The pollution from industrial effluents/sewage has already gripped many industrially developedcities that this aspect needs special attention. In order to make appropriate and efficient plans and strategiesto combat the menace of the nitrate pollution of ground water, concentrated research efforts are necessaryto generate information related to the status of pollution, its nature and possible impacts on the system.Since it impossible to have too many field studies, models must be modified and/or developed throughintensive detailed field investigations and validated for a diverse set of conditions. It will enable extrapolatingthe results to other locations. At present, there is scarcity of both under the Indian context.

There is no benefit of the reactive N created during fossil fuel combustion because NOx are formedduring combustion either through oxidation of fossil-organic reactive N in the fuel or through oxidationof atmospheric N2. There can be several options for significantly reducing NOx emissions. Using analternative method to provide energy or by eliminating NOx and other reactive N species from thecombustion products are possible (Bradley and Jones 2002, Moomaw 2002). It is now technically feasibleto decrease reactive N creation from fossil fuel combustion to a point where it becomes just a minordisturbance to the reactive N cycle (Galloway et al., 2003).

Efforts to improve energy efficiency, measured in terms of the services obtained per unit of fuelconsumption, will be a major focus of environmental policy in India because anthropogenic emissionsof NOx are dominated by fossil fuel combustion. Change in the N cycle through emissions of NOx in


India as linked to the use of fossil fuel energy are likely to increase dramatically over the next severaldecades, unless there is a concerted effort to control fossil fuel consumption. Technological changes thateither increases efficiency of fuel combustion or removes nitrogen oxides from the exhaust stream shouldbe able to reduce the total amount of N emitted, but complete solutions are closely linked to the developmentof non-polluting alternative energy sources.

Assessment of various N pools, N-cycling and N mass balance studies on all geographical and timescales are characterized by high variability and uncertainty. The data sources, models/methods adopted,change in cropping pattern, biomass burning, environmental and climatic factors introduces variabilityin the measurements at different levels and extend. Since N2O emission from soils is a key source ofN containing green house gases emissions in India, it is necessary to develop appropriate emissioncoefficients through measurements covering the different seasons in the diverse cropping systems of thecountry. Thus it is important essential to properly understand different kinds of N fluxes and to quantifyvariations in inputs and losses as ranges rather than as single values.

Human impacts on the N cycle strongly depend upon the rates at which fixed N is denitrified toN2 in land and aquatic systems. Unfortunately, a quantitative understanding of denitrification rates invarious managed and unmanaged terrestrial and aquatic environment is largely missing. This is probablythe biggest obstacle in accurate modeling of the N cycle. In addition to this, in India, climatic conditions(air and soil temperature, precipitation, wind and relative humidity) vary with seasons and strongly influencefluxes of N2O emissions and NH3 volatilization. Accurate estimates can be obtained by means of modelsimulations in conjunction with observations at large scales and linking of point measurements to spatialdata sets.

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ABOUT THE BOOK

ABOUT THE AUTHORS

• Bijay Singh • Mithilesh K. Tiwari • Yash P. Abrol


Professor Bijay Singh, ICARNational Professor, has been workingon different aspects of nitrogen inrice-wheat cropping system for morethan two decades. His contributionson nitrogen balance in soil-plantsystems have lead to betterunderstanding for (i) enhancingnitrogen use efficiency in rice-wheatcropping system (ii) fertilizer nitrogenrelated environmental pollution, and(iii) integrated nutrient management.He is a fellow of Indian NationalScience Academy, National Academyof Agricultural Sciences and IndianSociety of Soil Science. He is decoratedwith several awards notably the RafiAhmad Kidwai Memorial Prize ofICAR. He is continuing work onincreasing fertilizer nitrogen useefficiency in rice and wheat at PunjabAgricultural University, Ludhiana.

Dr. Mithilesh K. Tiwari is Director ofthe South Asian Regional Centre of theInternational START Programme that isresponsible for nurturing regionalcooperation for studies on GlobalChange with particular emphasis nowon Climate Change Adaptation. Heheads the Centre on Global ChangeProject of CSIR and the Radio andAtmospheric Sciences Division,National Physical Laboratory at NewDelhi. He is an active Core TeamMember of the Indian Nitrogen Group.He has extensively contributed to thegrowth of several major national levelresearch programmes in space sciences.His research interests are atmosphericenvironmental change processes andimpacts. Currently member of INSA’sNational Committee for SCAR, he alsoserved the National Committees for IGBPand COSPAR.

Professor Yash P Abrol, formerly Headof the Division of Plant Physiology atthe Indian Agricultural ResearchInstitute, New Delhi, subsequent toserving as CSIR Emeritus Scientist andINSA Senior Scientist (1996-2001; 2001-2005), is at present associated with theDepartment of Environmental Botany,Hamdard University, New Delhi asAdjunct Professor and INSA HonoraryScientist,. He has immensely contributedto nitrogen research and has publishedprofusely in reputed journals. He isactively involved in organizing INDIAN

NITROGEN GROUP under the aegis ofthe Society for Conservation of Nature.He is a Fellow of the INSA, IndianAcademy of Sciences, National Academyof Sciences and NAAS. He receivedseveral awards notably ICAR NationalFellowship, FAI Dhirubhai MorarjiMemorial, R.D. Asana, Sukumar Basu,VASVIK and FICCI awards.

In Agriculture, Industry and Environment in India

Precipitation

Gaseous Losses

Nitrates Ammonium

Nitrites

Organic Residues

Organic Matter

Clay Minerals

Plant ConsumptionDenitrification

Leaching

Nitrificationthrough bacteria

Fixation

Mineralization

Jammu &Kashmir

HimachalPradesh

Uttaranchal

Rajasthan UttarPradesh

Sikkim

Bihar

WestBengal

TripuraMizoram

Manipur

NagalandMegalaya

Assam

ArunachalPradesh

Orissa

JharkhandMadhya PradeshGujarat

Mumbai(Bombay)

Maharashtra

AndhraPradesh

Goa

Lakshdeep

Karnataka

KeralaTamilNadu

Chennai (Madras)

Andaman & Nicobar

Kolkata(Calcutta)Chha

ttisgar

h

DELHI

Punjab

Atmospheric N2

WetlandVegetation

Denitrificationby denitrifyingbacteria

AssimilationNitrification bynitrifying bacteria Nitrites

(NO2)

Nitrogen(NO2)

Ammonium (NH4+)(NH4

+)

Nitrification bynitrifying bacteria

Open Water

Oceans containing CO(NH2)2

Seagull

Decayingdead animal

Nitrogen fixing soil bacteria

Decomposition(Bacteria andfungi)

Ammonification

The current status of reactive nitrogen which consists of all biologically, chemically and radiatively active nitrogencompounds in terrestrial, coastal and atmospheric realms and development of technologies to minimize nitrogenimpacts on the environment needs to be addressed in the right perspective. The development of policy to controlunwanted reactive N release in the environment is difficult because much of the reactive N release is relatedto food and energy production and reactive N species can be transported great distances in the atmosphereand in aquatic systems.

This publication is an outcome of the activities of the Indian Nitrogen Group, a national network of scientistsconcerned with issues related to reactive nitrogen. It presents an overview of reactive nitrogen in agriculture,industry and environment in India. Since reliable quantitative information about several aspects of reactivenitrogen in the country is not yet available, it should prove very valuable for the scientific community in termsof initiating projects to fill the gaps. It should also help planners in agriculture, industry and energy productionto guide future expansion in the economy in a way that the delicate balance between inputs and outputs ofreactive nitrogen in the environment is maintained.

Reactive N in Agric Environ Industry in India

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