Global nitrogen budgets in cereals: A 50-year assessment for maize, rice, and wheat production systems

Authors

J. K. Ladha, International Rice Research Institute
A. Tirol-Padre, International Rice Research Institute
C. K. Reddy, International Rice Research Institute
Kenneth Cassman, University of Nebraska-LincolnFollow
Sudhir Verma, Dr. YS Parmar University of Horticulture & Forestry
D. S. Powlson, Rothamsted Research
C. van Kessel, University of California, Davis
Daniel de B. Richter, Duke University
Debashis Chakraborty, Indian Agricultural Research Institute
Himanshu Pathak, Indian Agricultural Research Institute

Date of this Version

2016

Citation

Scientific Reports, 6:19355, DOI: 10.1038/srep19355

Abstract

Industrially produced N-fertilizer is essential to the production of cereals that supports current and projected human populations. We constructed a top-down global N budget for maize, rice, and wheat for a 50-year period (1961 to 2010). Cereals harvested a total of 1551 Tg of N, of which 48% was supplied through fertilizer-N and 4% came from net soil depletion. An estimated 48% (737 Tg) of crop N, equal to 29, 38, and 25 kg ha⁻¹ yr⁻¹ for maize, rice, and wheat, respectively, is contributed by sources other than fertilizer- or soil-N. Non-symbiotic N₂ fixation appears to be the major source of this N, which is 370 Tg or 24% of total N in the crop, corresponding to 13, 22, and 13 kg ha⁻¹ yr⁻¹ for maize, rice, and wheat, respectively. Manure (217 Tg or 14%) and atmospheric deposition (96 Tg or 6%) are the other sources of N. Crop residues and seed contribute marginally. Our scaling-down approach to estimate the contribution of non-symbiotic N₂ fixation is robust because it focuses on global quantities of N in sources and sinks that are easier to estimate, in contrast to estimating N losses per se, because losses are highly soil-, climate-, and crop-specific.