Recent Advances on the Technologies to Increase Fertilizer Use Efficiency.pdf

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ScienceDirect

April 2008

Agricultural Science s in China

2008, 7(4): 469-479

Recent Advances on the Technolog ies to Increase Fertilizer Use Efficiency

1 Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing

100081

P.R.China

2

Key Laboratory

of

Plant Nutrition and Nutrient Cycling, Ministry of Agriculture, Beijing

100081

P.R.China

International Plant Nutrition Institute IPN I) China Program, Beijing

100081

P.R.China

Abstract

To increase fertilizer use efficiency (FUE) and to minimize its negative impact on environment have been the focal points

in the world for a long time. It is very important to increase FU E in China for its relatively low F UE and serious losses of

nutrients. Recent advances of the technologies to increase FUE are reviewed in this article. These include site-specific

and real-time nitrogen management, non-destructive quick test of the nitrogen status of plants, new types of slow release

and controlled release fertilizers, site-specific nutrient management, and use of urease inhibitor and nitrification inhibitor

to decrease nitrogen losses. Future outlook in technologies related to FUE imp rovement is a lso discussed.

Key words: fertilizer use efficiency, site-specificheal-time nitrogen manag ement, slowly release/controlled release fertilizer,

site specific nutrient management, ureasehitrification inhibitor

INTRODUCTION

Fertilizer is the vital input material for the sustainable

developm ent of crop production and plays an importan t

role in food security. The worldwide experiences in

agricultural development have proved that rational

fertilization is the most efficient and important measure

for increasing crop production. The am ount of fertilizer

consumed in C hina has been increasing by 4 each

year since 1980. At present, China has become the

worlds largest producer and co nsumer of fertilizer.

The amount of ferti l izer consumed in China has

approached one-third of the total am ount of

the

world

consumption, although the arable land of the country

only occupies 9 of the worlds total. Due to the low

fertilizer w e efficiency (FUE ), the nitrogen loses

heavily through volatilization, leaching, and runoff.

Taking the example of consumption of 2lmillion tons

of pure nitrogen each year, and 45 of the amou nt is

lost (Li et al 1998). The total loss of nitrogen can

reach 9.45 million tons each year, which equals to

20.

5 million tons of urea. The heavy loss of fertilizer has

triggered a series of environmental problems. In some

intensified agricultural areas in the north, the irrational

application of nitrogen has led to the overrun of nitrates

in the groundwater. These examples have been

repor ted now and then. In some econom ical ly

developed areas in the sou th, the overapplication of

nitrogen and phosphorus fertilizers has contributed to

eutrophication of surface water. Besides, there are

other examples of environmental problems resulting

from irrational application of fertilizer, such as the

accumulation of nitrates in vegetables, the increased

emission of nitrous oxide in the air, and red tide of

southern inshore cities. Thereafter, to increase FUE

h a s s i g n i f i c a n t me a n i n g s f o r t h e s u s t a i n a b l e

developm ent of agriculture.

This paper is translated from its Chinese version in

Scientia Agricultura Sinica.

YAN Xiang,

Assistant Professor,

Tek +86-1068918700,E-mail:

[email protected];Correspondence JIN Ji-yun,

Professor

Tel: +86-10-68918o00,E-mail:yjinacaas.

ac.cn

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Xiang et al.

THE PRESENT STATE OF FUE IN CHINA

Fertilizer use efficiency is an im portant index to judge

whether the fertilizer has been rationally applied. The

FUE on a large-scale can normally be estimated through

two methods. One is referred to as a macro approach.

With this method , the amoun t of fertilizer applied and

the yield of grains in the tested area are collected , along

with variables of the yield and the fertilizer applied in

unit sown area each year, and the maximum yields from

unfertilized and fertilized areas. The FEU can be

estimated based on th e above information (Chen T B

et

al. 2002). The result calculated in this way normally

differs from the number that is actually measured from

the field. The more commonly used method is through

field research. Since field experimentation s influenced

by many factors, such as soil, water, and weather,

hence the tested FUE varies with areas and crops.

Therefore, a considerable number of field trials is

required with this approach.

Zhu and Wen (1992) reported that nitrogen use

efficiency (crop recovery of N in the first crop) by

wheat, rice, and maize ranging from 28 to 41 in China

after summarizing 782 field tests. The phospho rus use

efficiency (crop recovery of P in the first crop) was

much lower than that of nitrogen and potassium

fertilizers. This was due to its chem ical reaction with

the iron, aluminu m (in the south), and calcium ions in

the soil after its application. Th e phosphorus use

efficiency of the first crop varied between 10-25 in

China, as shown by the large-field test and potted-plant

tests, including isotopes tracer tests (Xiong and Li

1990). According to the statistics of 849 large-fie ld

tests in the entire country offered by the Institute of

Soil Science, Chinese Academy of Scienc es, Nanjing,

the phosphorus use efficiency by rice was 8-20 , with

an average of 14 , the number by the wheat was 6-

26 . The potassium use efficiency in China was higher

than that of phosphate fertilizer, and the number was

roughly 50 Li

f al

1998; Zhu and Wen 199 2).

Results from a total of 165 field trials of wheat, corn,

and rice, tested in

50

selected villages in 20 provinces

in China in 20 2- 20 05 ndicated that the N use efficiency

of the first crop ranged from 8.9 to 78.0 with an

averag e of 28.7 ; P use efficiency of the first crop

ranged from

3.0

to 49.3 with an average of 13.1 ;

and that of

K

ranged from 4.5 to 82.8 with an average

of

27.3 . It can be seen that the FUE in general in

China is rather low.

C O N V E N T I O N A L A PP R O A C H T O

INCREASE FERTILIZER USE EFFICIENCY

The commonly used measures to increase FUE in

agricultural practice can be summed as following: 1.

Right rate. When the level of nitrogen fertilizer

application is low, the crop yield will increase with

increasing amount of nitrogen fertilizer. When the

amou nt of nitrogen fertilizer exceeds the limit, the c rop

yield will decrease instead of increase. At the same

time, N loss will increase with the increased application

rate of nitrogen fertilizer, and the nitrogen use efficiency

will drop. Hence, the amount of nitrogen fertilizer

applied should be controlled in a right range. 2. Control

of fertilizer application along with water. Water plays

an im portant role in the process of nitrogen circulation

and its absorption by crops. In actual practice,

appropriate nitrogen and water application should be

considered together, and the features of crop growth

at different stages should be taken into conside ration.

Comprehensive approach is often propitious to increase

FUE. In paddy f ie ld manag ement , cer ta in new

approaches, such as applying fertilizer without water

stand in the field and stimulating N movement w ith

water are often used to improve FUE. 3 . Deep

placement and split application. Deep placement is one

of the best practices to im prove fertilizer use efficiency

with stable effect, Research revealed that deep placement

of ammonium bicarbonate and urea increased crop yield

by 2.7-11.6 , comp ared with surface application, at

the sam e time, nitrogen use efficiency was also increased

by 7.2-12.8 (Ga o and

Lu

2006; Huang and

Pu

2006).

Com pared to one-off application, split application can

increase nitrogen use efficiency and decrease the losses.

4. Balanced fertilization. Balanced application of

nitrogen, phosphorus, potassium, along w ith secondary

and micro-elements can guarantee a balanced supply

of all the essential nutrients for norma l growth. This

technique can avoid inefficiency of fertilizer due to

imbalanced nutrients. The key point of this technique

is to control the prop ortion of different nutrients, and

the balance between the crops demand and the amo unt

Q2008 CAAS. All

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Recent Advances on the Technologies

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Increase Fertilizer Use Efficiency

41

of fertilizer applied at all stages of grow th.

With the development of technology and science,

new techniques and approaches have been applied in

the agricultural production practice. Apart from

tradi t ional methods, new techniques have been

developed such as site-specificheal-time nitrogen

management, slow releasekontrolled release fertilizer

(SRKIW), site-specific precision nutrient management,

and ureasehi trification inhibitor. Those techniques play

an important role in decreasing fertilizer loss and

increasing FUE. Though some techniques have not

been applied widely in China due to various limitations,

their potential is quite vast. Hu and Li (2005) pointed

out that precision farming has triggered a series of

changes in the way of thinking and agricultural

management, and these changes would become the

technical basis of the sustainable development of

agriculture, rational utilization of resources, and

meliorating bio-environment; thus they had great

significance.

NEW DEVELOPMENT IN INCREASING FUE

Site-specific/real-time nitrogen management

(SSRTN

M)

Traditional methods of recommendation in fertilization

involve gathering, treatment, testing, and analysis of

samples, and calculation of data, which cost a lot of

human and material resources with low output. Many

field crops display symptoms obviously under the

nitrogen stress. The old leaves lose green color if the

plant lacks nitrogen. On the co ntrary, if the nitrogen is

over-applied, the leaves appear dark green and turn old

slowly. This physical feature is used to develop a new

method, that is by observing the color of leaves to

evaluate the nitrogen nutrient state. This method was

developed in the 1990s and has been widely used in

practice. Minolta chlorophyll meter (SPAD)

is

used to

evaluate the nutrient state of plants and proper advice is

given to fertilization. In this way, chlorophyll relative

content

is

detected without hurting the plant. The

working mechanics of SPAD is to evaluate the nitrogen

nutrient state on the basis of the relationship between

chlorophyll content and nitrogen content in the leaves.

The concrete steps are as follows: First, the chosen

leaves of the tested plant

are

inserted into the SPAD to

get the chlorophyll value by sensitization; hen chlorophyll

value can be gained

on

the basis of the relationship of

nitrogen content in the plant; finally the nitrogen content

in the crop can be obtained.

RTNM and SSN M are new techniques of managing

nitrogen fertilizer developed on the basis of using SPAD

to guide the fertilization. Th e earliest application of

n i t r o g e n f e r t i l i z e r m a n a g e m e n t w a s f o r t h e

recomm ended fertilization of rice. SPAD value which

is gained through testing the color cha nges at different

stages is compared with the scale of recommended

amou nt of fertilizer to decide wh ether to add fertilizer

and the amount to add (Peng

et

al.

1996). The most

obvious advantage of this method

is

that the time and

amount of fertilizer applied fit well with the actual

demand of the crops. Peng et al. (1996, 2002) had

used SPAD to g uide the r ice n i t rogen fer t i l izer

management. Their research showed that the SPAD

mode can increase nitrogen agronomic efficiency

significantly than the fixed-term n itrogen application.

SSNM decides the amount of fertilizer that would be

given to the crops

on

the basis of comprehensive

elements. Under this way, valid supplementofnitrogen,

phosphorus, and potassium in the soil, the yield, the

nutrient consumed by stalk, and weather feature are

taken as necessary index, which are analyzed through

fertilization decision system, and then the best am ount

of

fertilizer application is decided as the scale (Peng

et al.

1996; Liu et

al.

2006). Finally, the amount of

fertilizer to be used i s decided accord ing to the SPAD

value of the leaves.

It is very important to decide the SPAD threshold.

Peng et al. (1996) claimed that SPAD value 35 i s suitable

for most tropical indica rice breeds. He et

al.

(2007)

demonstra ted that SS/RTNM could readjust the

relationship between th e yield and quality of rice.

Whereas, the key step is to decide the proper scheduled

SPAD threshold on the basis of the features and qualities

of breeds of rice. Under his experimental conditions,

SS RT NM model recommends SPAD38-39 for one

var ie ty , and SPAD 35-37 fo r ano the r va r i e ty ,

respectively.

When SPAD is used to diagno se the crop nitrogen

nutrients state under field conditions, different periods

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472 YAN

Xiang

et al.

and positions tested lead to various results. Hen ce,

proper periods and positions should be chosen for the

diagnosis. Otherw ise, the result will be affected.

Scientists claimed (Li

Z

H et

at.

2005) that the best

diagnosis periods for maize is from 9th-leaf to 10th-

leaf period; and the be st position is the m iddle part of

the uppermost leaves. The SPAD value of chlorophyll

and the total nitrogen content in plant and nitrogen rate

are closely related. The relationship between them can

be used as a

tool

for the diagnosis of nitrogen nutrients

state

of

maize. How ever, there are gaps between the

SPAD results which are gained from different test sites.

In this case, an independent diagnostic index shou ld be

established. Another choice is to use relative chlorophyll

SPAD value of leaves to presen t the state of nitrogen

nutrients of crops. When the latter method is used,

SPAD will achieve 66.7 in prediction precision for

recommended fertilization for sum mer maize.

SPAD is characterized by its convenience, swiftness,

efficiency, and not causing trauma. The most important

point is that it can less en the rate of nitrogen fertilizer

and raise

FUE

At present, SPAD has been widely used

in rice (Peng

et

al. 1993). wheat (Wood et al. 1992),

rapeseed plant (Zhu t

al.

2006), and maize (Li

Z

H

et al.

20 05 ). It is shown by Liu

et al.

(2006) that

SSNM

can reduce the rate of fertilizer applied by 38.7-

41.3 , raise the outpu t by 2.5-3.5 , and increas e

nitrogen use efficiency and physiological nitrogen

transformation by 34.0-39.5 and 46.1-61.6 ,

respectively, when compared with the traditional ways.

Despite many advantages over the traditional practice,

SPAD has its own limitations. It can only test an area

as small as 6 mm2 so the numb er of samples it can test

is limited. Thereafter, the nitrogen content tested using

this method is just a rough estimate based on those

limited points. Com paratively, spectrum analysis

technique demonstrated its advantages by its sw iftness

and economy. Its mechanism is that malnutrition in

plants causes changes in color, thickness, and shape of

leaves and those changes triggers spectrum reflection

traits. A test model is quickly set up to evaluate the

nutrit ion state of the plants, through which the

information of plant nutrients conten t spectrum analysis

technique is obtained. This technique is one of the

necessary and ind ispensable techniques

in

variant

fertilization and irrigation of precision farming. It suits

better than SPAD in supervizing the crop nitrogen

content

in

large fields.

Slow release/con trolled rel ease fertilizer (SR/

CRF)

One of the reasons for the low FUE is the imbalance

between the time and in tensity that fertilizer gives off

its nutrient and the demands of crops. Slow release/

controlled release fertilizer is produced by controlling

the water-solubility of comm on fertilizer. The nutrient

release

is

efficiently controlled or delayed by improving

the fertilizer itself, which m atches the release time and

intensity with the demands of crops (or basically match)

(He

et

al.

1998). This method can assort with the

demands of nutrients by crops and the supply

of

nutrients, therefore increase the yield. It is believed to

be the quickest and most convenient way to decrease

the loss of fertilizer and increase FUE (Table).

SRF mainly delays the release of the nutrients and

extends the fertilizer effect period. CR F combines

acceleration and delay of the nutrient release from the

fertilizers, it can control the spe ed of nutrient su pply.

Urea-formaldehyde fertilizer is the earliest SR F in the

world which was invented in 1924. CRF appeared with

the development of SRF. The earliest SRF in China

was developed by the end of 1960s and the beginning

of the 1970s. The Institute of Soil Science, Chinese

Academy of Sciences, successfully invented granular

a mmo n i u m b i c a r b o n a t e l o n g - t e r m a mmo n i u m

Table

Comparison of crop yield and fertilizer use efficien t between con trolled hlow release fertilizer and common fertilizer

Site

Crop

Fertilizer

Yield increase compares

with control 96)

FUE

increase compares

with control ( )

. .

Longkou City, Shandong

MaiZe

Polymers coated controlled-release 36.2-4 6.6 12 .5-2 5.2 1

(Ma

er al. 2006)

(Liu

et

af 2002)

Sanyuan County, Shannxi Winter wheat

FMP

coating urea 9-1546 15 -1 68

(Fan and Liu 2004)

nitrogen fertilizer

nitrogen fertilizer

Changsha City Rice.

I5N

labled controlled-release 25.5 34.9

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Recent Advances on the Technologies to Increase Fertilizer Use Efficiency

47 3

bicarbonate and long-term urea coated by calcium

magnesium phosphorus fertilizer followed by other kinds

of SIUCRF. Beijing Institute of Landscape Gardening

and Beijing Chemical Industry Research Institute

developed resorcinol-formaldehyde resin-coated

compound fertilizer jointly in 1985; the Institute of

Agricultural Modernization, Chinese Academy of

Sciences (Now the Center for A gricultural Resources

Research, Institute of Genetics and Developmental

Biology, CAS) invented coated urea two years later;

technical faculty of Z hengzhou University manag ed to

produce coated SR/CRF in recent years ; China

Petroleum and Chemical Cooperation and China National

Hybrid Rice R& D Center jointly developed the latest

type of hybrid-rice-specific SCR F.

There are many types of SR/CRF which can be

divided into three types as follows. The first type is

coated SIUCRF which has two sub-types: 1)mineral

coated fertilizer (mainly con sists of sulfur, silicate,

gypsum, and p hosphoric acid), and

2)

organic polymer

coated fertilizer which mainly consists of natural high-

molecular mater ia ls (such as s tarch, f ibr in , and

caoutchouc), compound high-molecular materials (such

as polyethylene and PV C), and semi-compound high-

molecular materials (such as ethyl cellulose). -The

second type is constituted by coa ting material SIUCRF

which

is

a kind of compound of mono-/multi-nutrient

coating another kind of nutrient. Com mon coating

materials are urea, humic acid, potassium sulfate, and

diatomite. The third type is compoun d low-grade

solubility SIUCRF with finite water-solubility, such as

urea-formaldehyde fertilizer, IBDU, a nd FMP.

Features of nutrients release are a significant index

for evaluating the quality of SWC RF. Many researchers

have done a lot of research with this regard both in

theory and in field experimentation (Zhai

et

al.

2002;

Du et

al. 2003,2005).

However, there is still a vacancy

concerning the standard of product quality and method

of evaluation. The features of nutrients release of

SR/

CR F are affected by a series of environmental elemen ts,

such as crops nutrients peculiarity, soil texture, fertilizer

quality, moisture, and temperature. The features of

nutrients release vary a lot according to different types

of SIUCRF. The curve feature of organic nitrogen CRF

is a q uick release at the beginning and a slow release in

the last quarter or one third part, which is quite different

from that of S type. The model of polymer coated

CR F is parabola-shaped, linear, and S-shaped. This

kind of fertilizer is suitable for short-term crops,

perennial plants, and trees during their transitiona l period

from hibernation t o biogas, and is able to supply

nutrients when they are needed. It is believed that the

ideal curve shou ld be a com bination of S-shape and

linear-shape so as to avoid the explosive release at

the beginning and the dragg ing-on effect at the end.

There are two common methods to evaluate the

nutrients release features of SW CRF: w ater/solution

solubility method and soil leaching method. In the first

method , SIUCRF is extracted in water or salt solution,

then the solubility within a given period of time is

calculated. This is the most common ly used method,

because it is easy and quick to use. However, there are

some discrepancies between this method and the real

practice due to different situations. The latter simulates

fertilizer-soil system to measure the nu trients content

that has been released from the fertilizer. This method

is more clo se to the reality, because it reflects the release

feature of fertilizer in the soil solution.

In the past

10

years, an increasing number of

developed countries paid more attention to the damage

caused by overuse of fertilizers. The labor price is

very high in the developed countries. Hence, the

SR/

CR F which saves labor and reduces environment

pollution has been undergoing quick development. From

1983 to 2005,

the increase of SIUCRF in the USA

was

4.2

er year; that in deve loped European countries

was

2.8

per

year,

In

2005,

the worlds total product

of SWCRF was

7.28

million tons, amongst which the

USA consumed

4.95

million tons which occup ies 68

of the worlds total consum ption. In many countries,

due to the high price, SWCR F is mainly used in non-

agricultural crops, such as flowers, lawns, golf cou rses,

seedling nursery, and cash crop with high added value.

Only a small portion of SIUCRF is used in large field

production. Therefore, SWC RF has not really played

its role in agricultural production.

SIUCRF

is

still at the initial stage of research and

development in China. Though some of the techniques

have reached advanced level of the world, the entire

situation still lags behind (Zhang et

al. 2005).

The

supporting equipments are relatively underdeveloped.

Th e techniques are kept secret amongst research

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institutes. Different institutes develop their coating

technique individually with no exchange amongst

themselves. Therefore, there are many cases of

repetition

on

low levels and retard development. SW

CRF produced in China cannot meet the needs of

matching the release and demand of crops. The fertilizer

cannot reach the index of self-controlled release with

high technique contents. Mo reover, the prices of SW

CRF are much higher than that of normal fertilizer,

which is hard to be accepted by farmers. Due to the

above-mentioned factors, it is difficult to implement

the SWCR F in practice. At present, SWCRF occupies

only a small portion in the total amo unt of production

and consumption of fertilizer. Judging from the present

situation, it is very hard to realize the target of increasing

FUE and decreasing the loss of nitrogen fertilizer.

Whe reas, the consum ption of fertilizer keeps growing

in China; it is essential to guarantee the quality of

products and to m eet the deman ds of environmental

friendliness,energy-saving,and sustainabledevelopment

of economy. SW CRF is undoubtedly one of the best

solution for this situation. The key step is to solve the

urgent problems as follows:

1)

to lower the prices of

SC F to reduce the cost by farmers;

2)

to establish and

publish necessary regulations and standards of the SCF,

such as the releasing function to guarantee the quality

of SCF; 3) to set up a national research platform for

the com monweal system (public appropriate funds with

research institutes and implementing organizations

participating) and enterprise system (w ith enterprise

investment, development center, production and

consum er farmers participating) to solve the technical

problems arising from the conflicts between national

target, company target, and fann er interest (Zhang et al.

2005).

Farmland nutr ients precision management

technique

Precision farming is a revolution in agriculture by

combining modern spat ia l data technology and

agronomical technology. It precisely and elaborately

determines and manages the material that will be put

into the field according to the concrete conditions of

each operation unit. It turns the traditional high-

consumption and low-efficiency production model into

a high-efficiency and low -consumption style by saving

a lot of materials and protecting the environment (Hu

and Li 2005). Precision fertilization applies fertilizer

precisely an d timely according to the soil and crops

deman d pattern to meet the needs of crops at different

stages. It achieves the highest economic effect by

investing the least fertilizer; hence, it increases the

FU

and improves the ag ricultural eco-system.

Precision farming technology can be divided into four

parts concerning the implementation procedure:

obtaining field data, managing the data, analysis and

decision-mak ing, and decision application in the fields

(Zhao 2000). The field data can be obta ined by way of

traditional sampling, GPS (global position system)

guided sampling, and remote sensing. The precision of

GPS is up to a decim eter level and centimeter level.

The remote sensing is quicker than the previous two

methods, and it obtains continuous data rather than spot

data, which is more advantageous. It is becoming the

major means of obtaining data for precision farming.

G Is (geographic information system) establishes the

field management information system by processing,

analyzing, and trimm ing the data of soil and crops.

Other examples of G Is applications are field boundary

map management, soil fertility management, yield

dis t r ibut ion curve , and mana gemen t . Rela t ive

management software is under further development

(Zhao et al.

2003).

Precision fertilization is one of the most w idely used

and mature techniques in precision farming decision

analysis and decision-making. First, it obtains the data

of so il nutrient (such as available N, P, K, pH, organic

matter content) and the growth of crops. Second, it

makes out the diversity of field spatial property. Then

it reaches the decision of fertilizer application on the

basis of variable-rate fertilization d ecision analysis

system, the model of crop growth, and demand for

nutrients. Finally, it realizes the precision fertilization

by DGPS (differential geographic information system)

technology and variable-rate fertilization monitoring

system. Severa l experiments in Guangxi of China

showed that precision fertilization increases the nitrogen

use efficiency

on

rice and maize by

7.8 ,

average,

when com pared with traditional way of fertilization (Lu

and Wu 2004).

Regionalized balanced fertilization technique is

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Recent Advances on the Technologies to Increase Fertilizer U se Efficiency

475

developed on the basis of precision farming. It divides

a large field into different management units according

to the planting patterns, so il nutrient supply capacity,

fertilizer application status, agro-type, and soil texture

to implement recommended fertilization. This is an

effective approach developed to reach the m acro control

and improving the precision in fertilization for relatively

small- scale land operation system in China, and it helps

to realize the balanced fertilization, foster so il fertility,

and increase the FUE and output (Huang et al. 2002b).

The concrete steps are 1) o analyze the spatial variability

and distribution of soil nutrients by combined use of

GIs , GPS, and geosta t is t ics , so as to produce a

distribution map of soil nutrients; 2)

on

this basis, the

tested area is divided into different regions based on the

soil nutrient status and yield goal of crops; and 3) then,

balanced fertilization is recom mend ed for each region.

Regionalized balanced fertilization technique has been

used at different levels in terms of man agement units:

farms field level (Li

Y Y

et al. 2005), towns level (Huang

et

al.

2002a), and county level (Huang et

al.

2003).

For a relatively large scale (township level and above),

the key step is to select and decide the appropriate

sampling density and sam ple spatial scale, which will

affect the decision-making of regionalization of nutrient

managem ent. Regionalized balanced fertilization

technique is a good approach to help to realize relatively

precision nutrient management and balanced fertilization

in large areas under the separated small-scale land

operation in China at the present time.

After more than two decades of development,

precision farming has been used widely in developed

countries in Europe and America. A survey conducted

at 447 US farms showed that precision farming related

techniques was used in 70 of the agricu ltural

production. The techniques used were mainly precision

fertiliza tion, precision seeding, precision application of

pesticides, and yield monitoring (Jess 2004). Despite

the above fact, Zhao et

al.

(2003) pointed out that

precision farming technology system is still in its

enfant state; i t needs further development and

consummation. The check point of the research of

precision farming is the attainment of high-density field

data and the establishment of an app licable decision-

supporting system according to the data (Zhao et

al.

2003). The abov e two aspects are the key points in the

developm ent of precision farming in the future.

China started to search in the development of

precision farming since the 19 90s. Precision farming

model experiment areas have been set up in Beijing,

Shanghai, and Xinjiang. The situation in agriculture

production sector in China is so different from the

developed countries, in terms of farm ers education,

mechanization, operating scale, and so

on, so

that the

precision farming techniques developed in developed

countries cannot be adopted directly in China. It is

necessary to se t up a precis ion f ie ld nutr ients

management model which suits Chinas situations.

Nowadays, there are some urgent problems to be solved:

1)

The attainm ent of high density field data (mainly soil

nutrients). There are big discrepancies in farmland

nutrients due to the fact that the management

of

fields

is conducted by individual farmers in a relatively small

scale. The technique which quickly and precisely

collects, tests, and analyzes the data of soil chemical

properties on a large scale with a high density needs to

be developed. The presently used traditional sampling

and laboratory analysis methods are costly and time

and labor demanding. 2)The establishment of decision

support system of fertilization, that is how to solve the

deficiency

in

practicality, com patibility,and applicability

of the present expert system. 3) The development and

production of small-sized variable rate fertilization

equipment, which will help to realize and popularize the

precision variable-rate fertilization for small-scale land

operation in China.

U

easehit ificat on inhibitor

Urea is the most widely used nitrogen fertilizer in China,

It accounts for more than half of the total chemical

nitrogen fertilizer consumption each year. When app lied

into the soil, with the effect of urease in the soil, urea

will be hydrolyzed and the formed

NH,

an

be

volatilized,

which causes heavy economic loss and environmental

pollution. Urease inhibitor delays the water-dissolution

of urea and extends the time that urea diffusion at

fertilizer application spots. In this way, the density of

NH,

nd

NH,

n the soil can be lowered and the loss of

ammonia by volatilization being reduced.

There are more than a hundred types of urease

inhibitor after

30

years of development. The main types

02008

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reserved.

Published

by

ElsevierLM.


8/11

416 YAN

Xiang

et al.

include quinines, acidamide,polyacid, polyphenol, humic

acid, and formaldehyde. Amongst them, the most

widely used are

NBPT

thiophosphric triamide ) and HQ

(hydroquinone). NB PT restrains the volatilization of

NH, under alkaline soil and good vent ability conditions.

HQ can reduce the loss of NH, by delaying the

hydrolyzing of urea. Mo re importantly, it affects the

o n g o i n g t r a n s f o r ma t i o n o f u r e a h y d e o l y s a t e

(Wakabayashi

et

al. 1986). H Q receives wide attention

for its low price compared to other urease inhibitor (Yu

and Zhang 2006; Wang 2002; Li 2002). Iodic salt of

heavy me tals, such as Hg and Ag has been proved to be

effective urease inhibitor, but they cannot be used in

agricultural practice, because heavy metals can cause

pollution to the soil.

Hu mi c a c i d u r e a s e i n h i b i t o r i s a k i n d o f

environmental-friendly urea synergist. The forepart

research and report concentrated on its effect on the

soil urease inhibitor and its effect on increasing the yield

(Lu and Wang. 1994; Liu et al. 1994a; Fan and Ye

1995). In recent years, scientists conducted research

on the effect of humic acid matter on physiological

metabolism. Cheng et at. (1995) claimed that under

the cond ition of low tem perature stress, fulvic acid could

enha nce the activity of SOD and CAT of Cole seed ling,

raise the ascorbic acid content, restrain the production

of MDA and relieve the damage on chlorophyl, and

maintain physiologic function of cells, to accelerate

photosynthetic rate and root activity, and lower

respiratory rate considerably. Liu et

al.

(1994b) and Li

et at.

(2004) discovered that humic acid matter could

improve the quality of crops. Coal humic acid could

improve the growth of crops by facili tating the

absorption of nitrogen and increase the FUE of urea

nitrogen besides its good effect inhibiting (Li et al 2004;

Gao

et

al. 2004). It has a good potential and is suitable

for further development due to its low price, rich source,

incontamina tion, and safety to p lants and soil.

Nitrogen fertilizer takes nitration reaction under the

action of edaphon in the

soil.

NH loxide s into

NO;

under the action of am mon ium oxidation bacteria, and

then oxides further into NO,- under the action of

ammonia-oxidizing bacterium. Nitrification inhibitors

can restrain the transformation

of

NH,+ into NO; and

NO;, then reduc e the loss of NO; by leaching. It can

also reduce

the

production of NO, g as due tonitrification

and denitrification, and reduce the loss of nitrogen

leaching, then increase the nitrogen use efficiency.

Normal nitrification inhibitors are cyanoguanidine

[dimeric of cyanamide, dicyandiamide (DCD) for short]

and

2-chlorine-6-(trichloromethyl)

yridine (nitrapyrin

for short). The DOW c ompan y in the USA developed

the latter into a product called N-serve due to the

instability of 2-chlorine-6. Sever al researches show

that the combination application of nitrification inhibitors

and nitrogen fertilizer can decrease the loss of nitrogen

and increase the nitrogen use efficiency. Shang and

Gao (1999) reported that the mixed application of DCD

and amm onium acid carbonate on wheat can restrain

the nitrogen am monium nitrifying into nitrate nitrogen

and the volatilization of amm onia. Th e research on

nitrapyrin conducted by O wens (19 81) discovered that

the loss of

NO;

by leaching fell from 48 to 35 when

nitrapyrin was applied compared to its absence. Wang

et

al.

(2006) investigated the effect on outlet of NO, by

N-serve and its comb ination with sands under different

soil water levels. The result indicated that the overall

outlet of NO, dropped by 65 when N-serve was

applied under low water condition (14.2 ); the overall

outlet of NO, fell by 62.1 when N-serve was applied

with sands under high water condition (28.5 ).

A

lot of research results have proved that single use

of urease/nitrification inhibitor can only restrain some

process of urea nitrogen transform ation, while a joint

application

of

them can c ontrol the overall process

so

as to decrea se the loss of NH, by v olatilization and the

loss of NO,-N by leaching and increase the WE. Jiao

et al. (2004), Chen et al. (2005), and Chen L J et al.

(2002) pointed out the HQ +DCD combination decreased

the soil activity of urea, and restrained the oxidation of

urea hydrolysis, and retained its exchange form as NH,

in the soil more effectively compared to the individual

use of HQ, D CD, ECC (nitrification inhibitor coated by

calcium carbide), and NBPT. Restraining the oxidation

reduc es both the accumulation of NO; as oxide, and

potential eluviations of NO;, hence controls the leakage

depth of NO,- into the soil within 5-10 cm. The

restraining can at the same time increase the total amount

of effective N in the soil, and enhance the abso rption of

N by crops. It is reported by some researchers that

when HQ DC D are applied together, the outlet of NO,

and CH,

are

reduced by 1/3 and 112, respectively (Zhou

02008 CAAS.

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rights

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9/11

Recent Advances on the Technologies to Increase Fertilizer Use Efficiency

477

et al. 1999).

Perfect urea seht rifim tion inhibitor should not only

restrain the vo latilization of

NH,

nd the loss of NO,-N

by leaching, but also have n o negative effect for the

growth of crops

so

as to guarantee full absorption

of

nutrition by crops and the best yield effect. This is an

important principle in filtering ureasehitrification

inhibitor. Despite that they have taken some effect in

agricultural production, inhib itors have not been widely

applied throughou t the world. In most countries they

are still under testing and research. The ir effects on

production are not stable and are easily affected by

factors, such as inhibitor dosage, fertilizer dosage,

environment temperature, pH and the quality of soil.

Moreover, most of them are high in price, have some

toxic on crops, and are likely to cause environmental

pollution. Hence, it is hard to apply them in agricultural

production on a large scale. The direction for the

agricultural scientists in

the

future is to develop highly-

effective, safe, cheap, and innocuous urease/nitrification

inhibitors.

EXPECTATIONS

In the second half of the twentieth century, China

managed and have successfully improved its agricultural

production to support the worlds 22 population by

9 of the worlds arable land, which has been highly

evaluated by

the

international comm unity. F ertilizer use

contributed greatly to the grains production in China.

At present, China is facing a great challenge in food

supply to support the increasing population with its

limited arable land in the twenty-first century. It is vital

for China to further develop techniques that continue

to increase crop yield, improve FE U and mitigate the

pressure on environm ent to guarantee the food supply,

and bio-environment protection. Therefore, i t is

recommended that the following tasks be reinforced.

1)

To

expedite the development of new types of fertilizer

and the upgrade of normal fertilizer; to develop low-

cost and high-efficiency coating materials and SR /CRF

for certain types of crop; to set up the standard for

quality assessment and environment evaluation of

SW

CR F; to develop the research on organic fertilizers

fermentation quickly at high temperature, and the

deodorization compound bacteria screening and

combination; to develop key techniques in high-

efficiency granular-making glue material; to conduct

research on organic and mineral compound fertilizer

production; to accelerate the key steps in the research

on liquid fertilizer (Jin

2005 .

2)

To

investigate the

ecological and physiological mechanisms of imp roved

FEU by crops, to develop new techniques to further

improve crop yield with high fertilize use efficiency, to

in tegra te and fur ther improve nutr ient resource

management systems that guarantees high yield and high-

quality crop production with h igh fertilizer use efficiency

and im proved environm ental quality. 3)

To

investigate

the physiological and genetic mechanisms of crop

genotypes

in

nutrient use efficiency discrepancy, to

improve crop nutrient use efficiency through the use

of bio-technology, to filter and cultivate new types

of

crop which bear genotypes that effectively utilize the

nutrient, to implement the m elioration of plant nutrient

characters so as to improve plant nutrient utilization.

4)To establish national and regional information

management systems and supervision platform of

nutrient resource utilization, to monitor the soil fertility

status and crop responses to fertilization at the n ational

and regional scales; to set up scientific fertilization

decision-making system and environment evaluation

alarming system,

so

as to realize rational allocation and

effective utilization of fertilizer resources on national

and regional scales.

Acknowledgements

This study was supported by the National Basic

Research Program of China (2007CB

109306)

and

International Plan N utrition Institute, China Prog ram.

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