Fig. 1. Calibration of the parameter C for wheat, barley, maize, and sorghum. For wheat and barley, the data are from Pullman, WA; for maize, data are from 1 yr from Derby et al. (2005) and from Huggins et al. (2001); for sorghum, data are from Kamoshita et al. (1998a). Wheat average harvest index (HI) and aboveground nitrogen concentration (N_t) were 0.42 (range 0.30–0.56) and 11.5 (range 8.1–16.7 g kg^–1); barley average HI and N_t were 0.43 (range 0.35–0.53) and 9.6 (range 6–15.3 g kg^–1); maize average HI and N_t were 0.55 (range 0.36–0.68) and 8.3 (range 5.1–10.8 g kg^–1); sorghum average HI and N_t were 0.37 (range 0.18–0.48) and 10.4 (range 6.3–15.8 g kg^–1). RMSE and MAD are RMSE and mean absolute difference between observed and predicted N_g.