The dirt on nitrogen, soil, and carbon—a step toward solving the enigma of soil N balance

8/2/2019 The dirt on nitrogen, soil, and carbona step toward solving the enigma of soil N balance

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Dr. J. K. Ladha

IRRI Rice SeminarSeries

Current position: Principal Soil Scientist, IRRI

Editorial BoardSits in the editorial board of several international journals. Currently he is the

regional editor ofBiology and Fertility of Soils.

Education and training PhD from Banaras University, India (1976)Post Doctoral Fellow, University of Dundee (1977-78)Post Doctoral Fellow, IRRI (1980-82)

Work experience Twenty eight years experience in international agriculture researchin agronomy/cropping systems, soil management, andsystem sustainability.

Actively involved in research, training/teaching, project development, andteam leadership.

Co-author of more than 179 research articles in international refereed journals,and editor of 13 books.

Presented 81 invited papers in 31 countries.Supervised 30 M.S. and Ph.D. students and 40 Visiting Scientists from 12

countries.


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Dr. J. K. Ladha

Research highlights International Agronomy Service Award (2011)

International Soil Science Award (2010)

International Plant Nutrition Institute Science Award (2009)

Frosty Hill Fellow of the Cornell University (2008),

CGIAR King Baudouin Team Award (2004)

CGIAR Chairmans Excellence Science Team Award (2002)

Young Scientist Award by the Indian National Academy of Sciences (1976)

Fellow

American Association for the Advancement of Science (2008)

American Society of Agronomy (2004)

Soil Science Society of America (2002)

Indian Academy of Agriculture Science (1999).


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Very Best Wishesfor a Happy 2012

Foggy and

Cold New

Delhi


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Synthetic nitrogen is good for thefather and bad for the sons- Dutch

saying

J.K. [email protected]

The Dirt on Nitrogen, Soil andCarbon - A Step Toward Solving

the Enigma of Soil N Balance


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Synthetic N The Dirt

Destroys soil carbon

Undermines soil health

Creates a kind of treadmill effect

Bleeds the soil

Not an ecological advantage but agravest liability

Fertilized to death


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OutlineKey Topics for TodaysDiscussion

1. Role of Synthetic Nitrogen- Food production and Environment

- SOM

Equilibrium Concept

Methods to Calculate Changes in SOC and SON

Does the long-term use of synthetic fertilizer N

lead to decline in SOM? Summary and Conclusion


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Global, Long-Term (1961-2010),

3 Major Cereals

3 Land Use 3 Climate

7

Role of Synthetic N - Outline

2. Construct Global N Balance byIntegrating 50 Years of NResearch Outputs


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8

0

500

1000

1500

2000

2500

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Reducing hunger

Improving nutrition

Sparing naturalecosystem from

conversion toagriculture

R,W,MProduction(mt) Increased by 3 times in 40 years

Source: (FAO, 2010)

Global Rice, Wheat and MaizeProduction


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-20

-10

0

10

20

30

40

50

60

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

9

Global N Consumption by Rice,Wheat, Maize

Year

Consumption

(mt)

Increased by 9 times in 40 years

Source: unpublished


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10

Region/ RENT

a

Crop Mean

Africa

Australia

Europe

America

Asia

Average

Maize

RiceWheat

Average

aRENT=recovery efficiency of fertilizer N based on total plant N (kg N

taken kg

-1

N applied)

Descriptive Statistics of N Recovery Efficiencyfor Cereals in Various Regions

0.63

0.46

0.68

0.52

0.50

0.55

0.65

0.460.57

0.55

Ladha et al, 2005


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11

46 65% REN in first crop

5.7 7.1% REN in five succeeding crops

Summary

20 40% REN in Rainfeds

30 50% REN in Irrigated

200 studies (with 500 800 datapoints) conducted across the globein a wide diversity of ecologies

Source: Ladha et al 2005 Ad Agro


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Humanactivities

130-150(60%)?

Accumulation of reactive N in

AtmosphereSoilsGroundwaterLand vegetation

OceansMarine sediments

N2

Unreactive Pool4 x 109 Tg

Biotic90-130

Biotic90-130

Preindustrial Industrial

Reactive Pool of N(N2 Fixation Tg/year)

EnvironmentalChallenge


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2050

Global population 50% >

Global grain demand 100% >

Global fertilizer demand 50-70% >


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Soil Organic Matter

SOM is recognized as a major factor controlling thecapacity of soil resources to deliver agricultural andenvironmental servicesandsustain human societiesfromlocal (fertility maintenance) to global (mitigation ofatmospheric carbon emissions) scales.

Soilorganic

matteras a

pool of

nutrients

component oforgano-claycomplexes

pool ofcarbon

pool of

energy

soil chemical

status

soil waterstatus

soil physicalstatus

soil biological

status


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SOM Equilibrium Gain and Loss Balance

Time (Years)

SOC orSON

Loss

Gain

Originalequilibrium


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Gain (input) and Loss (output)Pathways of SOC and SON

Photosynthesis (C)

Biological NFixation

Synthetic N

Organics (C & N)

Decomposition/

Mineralization/Respiration

CO2, CH4

Denitrification/Leaching/

Volatilization

N2, N2O, NO, NO3, NH3

Gain Loss


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Major Factors Affecting SOMEquilibrium

Cropping pattern/intensity

Tillage

Climate

Organic fertilization Synthetic N fertilization

Soil water content

Organic fertilization Synthetic N fertilization


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Synthetic Fertilizer N

Question:Does the long-term use of synthetic fertilizer Nlead to decline in SOM?

View # 1

Augmenting SOM by promoting plant growththereby increasing amount of litter to soil.

View # 2Enhancing loss of SOM by accelerating its rateof oxidation or decay.


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Knowledge Gaps

Piece mill effort

Lack of consistency in data analysis

Inadequate statistics

No global scenario


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Ecological processes are oftenslow and it is only through long-

term experiments they can befirstly detected and secondly

understood.

T.R.E. Southwood, University ofOxford (1994)

Long-Term Experiment: A Treasure


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Worldwide Coverage of 114 LTEs

Tropical (20)

Sub-tropical (42)

Temperate (52)

3000 0 3000


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Data Set

All experiments included a cereal-based croprotation

At least one rate of synthetic fertilizer N (oftenwith P and K) plus a corresponding treatmentwithout the application of N (i.e.,N+P+Kversus +N+P+K) within a study

Use similar soil depth at t=0 and t=1

114 LTEs from 100 sites globally


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Data Set : Sub - Groups

Climate (CL)

Land Use (LU)

Fertilizer Type (FT)


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Data Set

Duration and number of C and N datapoints

Duration (year) SOC SON

10 172 103

11-30 543 311

31-50 85 84

>51 117 82Total 917 580


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Statistical Analysis

Standardization allowed the elimination of

differences due to sampling of soils atdifferent depths and the associated bulkdensities among the studies.

All the data (primary and derived) were

analyzed using the SAS mixed modelprocedure (SAS Institute, 2001) and meta-analysis Meta-Win software (Rosenberg etal., 2000).

All the gravimetric and volumetric datawere converted to a percentage changeover time.


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t = 0

Time

SO

CorSONContent

t = 1

mgNkg-1

1000

800

600- F (Nct1)

+ F (Nft1)

No change

Methods to Calculate Changes in SOC andSON


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Nft1 - Nft0

Nft0X 100 = - 20%

1 A)=

t = 0 Time

SOCorSONC

ontent

t = 1

+ F

+ F (Nft1)

- 20 %

h d l l h i d


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t = 0 Time

SOC

orSONContent

t = 1

2) = ((Nft1 / Nct1) -1)) x 100 = + 33

(Nft1)

+ F

(Nct1)- F

+ 33%


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3) = ((Nft1/ Nft0) - (Nct1 / Nct0) x 100 = + 20 %


t = 0 Time

SOC

orSONContent

t = 1

(Nct1)

Nct0 (Nft1)

Nft0

+ 20 %


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Estimation of Responses of FertilizerN Input to SOC and SON

Three ways:

(1) Time Response (TR)

(2) N-Fertilizer Response (NR)

(3) Time by N-fertilizer Response

(TNR)

(1) Time Response (TR)

% difference in SOC and SON contentfollowing the application fertilizer betweentime (t) = 0 and t = 1

TR = [(Nft1 Nft0) / Nft0] x 100


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(2) N-Fertilizer Response (NR)

% difference of the final values of soil N and Cbetween fertilized and zero-N treatments

NR = (Nft1 -fertilized / Nft1-Control -1) x 100


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(3) Time by N-fertilizer Response (TNR)

% difference between the change in SOC and

SON in N-fertilized treatments compared withthe change in the zero N

TNR = [(Nft1 -fertilized / Nft0 -fertilized) - (Nft1-

control / Nft0-control)] x 100


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TR TNR

Assesses the impact

of whole system(tillage, residuemanagement,erosion, fertilizermanagement etc)

Specifically

assesses the impactof an N-fertilizeramendment


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Final (t = 1) Concentration of SOC and SON (g kg-1) -Primary Data from 114 LTEs (Mixed Model Analysis)

Fertilizer (FT) SOC SON

Control (zero N) 13.7b 1.3bSynthetic N 12.9b 1.3b

Organic N 17.7a 2.0a

Integrated (organic +synthetic N)

8.8c 1.1b Land Use (LU) SOC SON

Flooded 18.0a 2.2aFlooded dryland 7.8c 1.2b

Dryland 14.0b 1.3b

Climate (CL) SOC SON

Tropical 8.2c 1.0b

Sub-tropical 13.8b 1.6a

Temperate 16.9a 1.4a

Organic N 17.7a 2.0a

Temperate 16.9a 1.4a

Flooded 18.0a 2.2a

TR d TNR f SOC d SON i Mi d M d l


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TR and TNR of SOC and SON using Mixed Modeland Meta Analysis

Mixed model

Mixed model

Meta-analysis

Meta-analysis

TNR

- std error

TR TNR

- 95% confidence interval

- std error- 95% confidenceinterval

TR

%

ChangeinSOC

-20

-10

0

10

20

30

40

50

60

Zero-N Synthetic-N Organic-N Organic+synthetic-N

%

ChangeinSOC

-20

-10

0

10

20

30

40

50

60


%C

hangein

SON

-20

-10

0

10

2030

40

50

60

Zero-N Synthetic-N Organic-N Organic+

synthetic-N

%C

hangeinSON

-20

-10

0

10

2030

40

50

60


P t Ch i TNR f SOC ith L


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Percent Change in TNR ofSOCwith Long-Term Synthetic N Application

Flooded(95%CI)

Flooded dryland(95%CI)

Dryland (95%CI)

TNR 7 (3-11) 17 (12-22) 7 (5-8)

Tropical(95%CI)

Humid sub-tropical

(95%CI)

Temperate(95%CI)

TNR 16 (12-20) 11 (9-14) 3 (1-4)

SOC (g kg

-1

) 15.2 (13-18) 6.3 (6-9) 12.7 (12-13)

SOC (g kg-1) 6.7 (6-7) 11.4 (10-12) 15.9 (15-17)6.7 (6-7)

17 (12-22)

16 (12-20)

6.3 (6-9)

Land Use

Climate


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Summary and Conclusion

Overall, SOM content generally declined over

time but synthetic-N led to slower decrease,and not a further additional decrease

SOM decreased in a crop rotation fluctuatingbetween flooding and drying than in

continuous dryland or flooded systems Flooded rice soils accumulates high SOC and

SON because of lower residue decompositionand higher BNF

TNR approach is accurate to determine theimpact of long-term application of synthetic Non SOM


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Summary and Conclusion

Undoubtedly, the primary function ofsynthetic N in producing food forgrowing population is vital but its role

on long-term consequences on thesystem sustainability is equallyimportant as SOM plays multiplefunctions in maintaining soil quality and

ecosystem services


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Key PublicationsLadha, Dawe, Ventura, Singh, Watanabe, SSAJ 2000Ladha, Pathak, Krupnik, Six, van Kessel, Ad Agro 2005Ladha, Reddy, Padre and van Kessel, JEQ 2011Ladha et al, unpublished

Acknowledgement

The dirt on nitrogen, soil, and carbon—a step toward solving the enigma of soil N balance

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