Fig. 7. Simulated (a) dry mass surface crop residue and (b) total soil profile residual NO3–N against the observed values at three locations (summit position) in eastern Colorado for three rotations {wheat–fallow (WF): 1988–1999; wheat–corn (or sorghum)–fallow [WC(S)F]: 1988–1999; wheat–corn (or sorghum)–millet–fallow [WC(S)MF]: 1988–1993}. Values in parentheses are root mean square error (RMSE) (kg ha-1) and d values.