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. 2016 Jan 18:6:19355.
doi: 10.1038/srep19355.

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

J K Ladha  1 , A Tirol-Padre  1 , C K Reddy  1 , K G Cassman  2 , Sudhir Verma  3 , D S Powlson  4 , C van Kessel  5 , Daniel de B Richter  6 , Debashis Chakraborty  7 , Himanshu Pathak  8
Affiliations

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

J K Ladha et al. Sci Rep. .

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.

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Figures

Figure 1
Figure 1. Trends in global averages of fertilizer-N application rates in maize, rice, and wheat.
Figure 2
Figure 2. Trends in global averages of total N harvest by maize, rice, and wheat.
Figure 3
Figure 3. Global estimates of sources of N in crop harvest of maize, rice, and wheat production systems: total (Tg) for 50 years (1961–2010) with percentages and per hectare (kg ha−1).
Figure 4
Figure 4
Estimates of N inputs (a) and outputs (b) in initial (1961) and final (2010) years.
See this image and copyright information in PMC

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