perspectives on the nitrogen cycle

Perspectives on the Nitrogen Cycle

Peter VitousekStanford University

We are entering the

Anthropocene

“the geologic epoch in which the human species has emerged as a globally

significant force reshaping the face of Earth”

P.J. Crutzen 2002

Global Terrestrial N Budget(Galloway and others 2007)

“Natural” Biological N Fixation 70 - 100Lightning 5

Total Fixed Naturally 75 – 105

Inorganic N Fertilizer 100Crop N Fixation 30Fossil Fuel Fixation 25Industrial Uses of fixed N 20

Total Fixed by Humanity ~175

EPA Nitrogen Report 2011

United States Nitrogen Budget

Vitousek 1994

IPCC Third Assessment Report, 2001

1000 1200 1400 1600 1800 2000Year

Robertson and Vitousek 2009

Anthropogenic reactive N is distributed unevenly across Earth

In some areas we use far too little N, in others we release far too much – and both extremes damage the environment and threaten human well-being.

Kenya North China Midwest US Maize Yield 2000

N P All in kg ha-1 y-1

Fertilizer 7 8

Removal in harvested 59 7 products

Agronomic inputs minus -52 +1 harvest removals

Comparison of Nutrient Balances

Sanchez andPalm pers. communication.

double crop, w wheat Kenya North China Midwest US Maize Yield 2000 8500

N P N P All in kg ha-1 y-1

Fertilizer 7 8 588 92

Removal in harvested products 59 7 361 39

Agronomic inputs minus harvest removals -52 +1 +227 +53

Comparison of Nutrient Balances

Ju et al. 2009

Maize-Wheat double-cropping, North China Plain

Ju et al. 2009

Rotation w/soybean Kenya North China Midwest US

Maize Yield 2000 8500 8000 N P N P N P

All in kg ha-1 y-1

Fertilizer (plus N fixation) 7 8 588 92 155 14

Removal in harvested products 59 7 361 39 145 23

Agronomic inputs minus harvest removals -52 +1 +227 +53 +10 -9

Comparison of Nutrient Balances

David and Drinkwater perscommunication.

(Vitousek et al. 2009)

EPA Nitrogen Report 2011

Prof. Fusuo Zhang, Dean, College of Resources and Environmental Sciences, China Agricultural University

Maize-Wheat double-cropping, North China Plain

Ju et al. 2009

Yield and Fertilizer UseISSM versus Farmer Practice

Farmer Practice ISSM

Maize Yield (t/ha) 6.8 (1.6) 13.0 (1.6)

N input (kg/ha) 257 (121) 237 (70)

Yield per unit N added (g/g) 26 (20) 57 (13)

N inputs minus harvest removals (kg/ha) +127 (42) -12 (56)

Chen et al. 2011

From P. Johnes (personal communication)

We are entering the

Anthropocene

“the geologic epoch in which the human species has emerged as a globally

significant force reshaping the face of Earth”

P.J. Crutzen 2002