Click on image to view larger version.
Fig. 3. Illinois data for fertilizer N input (open square) (Brown, 1955–1963; Illinois Department of Agriculture, 1964–2005) and grain N removal (solid circle) in corn, wheat, oats, barley, and rye (Secale cereale L.), calculated as a 5-yr moving average. Grain N removal was estimated using on-line data (USDA, 2007) for hectares harvested and mean yield (Mg ha–1), and grain N concentration calculated from textbook values for crude protein (Martin et al., 1976), assuming 175 (wheat) or 160 (all other crops) g N kg–1 protein.
