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1. Is soil test useful for N management?2. Should we mine soil nitrogen?3. Is NUE as low as perceived?
Deli Chen1 *, Shu Kee Lam1, Arvin R Mosier1, Richard Eckard1,Rob Norton2, Peter Vitousek3
1 Crop and Soil Science Section, Faculty of Veterinary and Agricultural Sciences,The University of Melbourne, Australia *[email protected]
2 International Plant Nutrition Institute, Australia3 Department of Biological Sciences, Stanford University, USA
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1850 1875 1900 1925 1950 1975 2000 2025 2050
Popu
latio
n, b
illio
nsTimeline of Global Reactive N Creation by Human Activity
1850 to 2000
Cultivation
Haber Bosch
Galloway et al. (2003)
Population
Nr C
reat
ion,
Tg N
yr-1
N-Nutrient
N2 + 3H2--> 2NH3
BNF
Half of the world population fed by chemical N
Soil N plays an important role in soil fertility
Based on 15N studies, even in well-fertilised fieldsabout 50 % of plant N uptake is from the soil N pool
Gardner and Drinkwater (2009)
N removal(0.11 Mt)
Case 2: Inadequate N input
N input(0.39Mt)
N removal(0.54 Mt)
N input(0.29 Mt)
Case 1: Excessive N input
Example: wheat in Australia
Example: intensive dairy in Australia
Too much N vs. too little N
Australian wheat system
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1-0.
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3-0.
50.
5-0.
70.
7-0.
90.
9-1.
11.
1-1.
31.
3-1.
51.
5-1.
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7-1.
91.
9-2.
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1-2.
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3-2.
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1
Freq
uenc
y (%
)
Partial nutrient balance (PNB)(N uptake/unit of N applied)
• PNB > 1 = soil Nbeing mined
• 67% of PNB > 1
• “Autumn break”:Although soil testmay indicate soil Nis available, it is notsustainable withoutN input.
Effect of N rates
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Part
ial n
utrie
nt b
alan
ce(N
upt
ake/
unit
of N
app
lied)
N rate (kg N/ha)
Average application rate is 80 kg N/ha
‘PNB > 1’ occurs mostly when N rate < 100 kg N/ha
N lost / kg agricultural products
WheatAustralia China US
0.3 43.9 25.7
Liang et al 2016; Xia et al. 2016
Australian pasture system, excessive N input
N source 1990 2000 2012N inputs (average per farm) kg N ha−1
Cattle 1 1 1Forage 10 24 31Concentrates 24 54 81Fertiliser 18 39 71Legume N inputs 31 27 26Atmosphere 6 6 5N input total 91 151 214
N outputs (average per farm) kg N ha−1
Cattle 9 9 8Milk 28 40 49N output total 36 48 57
N input – output (kg N ha−1) 54 103 158N use efficiency (%) 40 32 26Dutch dairy farms: N input – output (kg N ha−1) 210
Stott and Gourley (2016); Schulte-Uebbing (2016)
Is NUE as low as perceived?
Yan et al. (2014)
Yan et al. (2014)
Fertiliser N application is based onperceived need (low NUE)
Fertiliser N application is based onmineralisable N
Case 1: Excessive N input
Is the depletion of N sustainable?
Paradox of mining soil N
Case 2: Inadequate N input
Should soil N be mined forever?
Does soil N build up?Is NUE as low as perceived?
N input < N removalN input > N removal
Should soil N be mined?
How long can soil N be mined?
ISSM High yield
Maize grain yield (tonnes/ha) 13 15.2
N input (kg N/ha) 237 747
N removed in harvest (kg N/ha) 250 292
Input – harvest (kg N/ha) –12 457
ISSM: integrated soil-crop system management Chen et al. (2010)
High yield maize production in the North China Plain
Framework
• Excessive N additions need to be halted, and the surplus Nshould be mined, at least for some time.
• For low N input systems,N should not be mined.
Challenges---Benchmarking & N footprint
• So far, no evidenced-based index for “Green”/sustainableagriculture products
• Can we develop Environmental Footprint TrueEnvironmental cost– To encourage and reward the more sustainable practices?
– To give more efficient producers marketing, pricing advantages
– To develop true environmental cost of agriculture productsproduction leading to payment/trading (Environmental Offset),Environmental (N) Credit
© Copyright The University of Melbourne 2016
Thank you
