Table 11.
Average global estimates of sources of N (kg N ha -1) in crop harvest of continuous maize, rice, and wheat production systems for 50 years and measured N removed in grain (1961–2010). Data in parentheses represent the percentages of the total N removed by cropa.
| Crop | Fertilizer | Soil N reserve | Manure | Atmospheric deposition | Crop residues | Seed | Calculated non-symbiotic BNF |
Total N removed in grain | Mean grain yield (t ha-1 yr-1) |
|---|---|---|---|---|---|---|---|---|---|
| Maize | 44.4 | 4.9 | 9.9 | 4.7 | 1.4 | 0.3 | 12.7 | 78.3 | 3.6 |
| Rice | 25.8 | -3.6 | 11.3 | 3 | 0.9 | 0.2 | 22.4 | 60.1 | 3.2 |
| Wheat | 24.9 | 5.6 | 6.5 | 4.1 | 0.8 | 1.2 | 12.7 | 55.7 | 2.1 |
| Mean | 31.7 | 2.3 | 9.2 | 3.9 | 1 | 0.6 | 15.9 | 64.7 | |
| (48.1%) | (4.4%) | (14.0%) | (6.2%) | (1.6%) | (1.1%) | (24.6%) | (100%) |
a
Adapted from Ladha et al. (2016).