Fig. 4. Observed and NLEAP-predicted residual soil NO^-₃–N (RSN) in the 0- to 0.9-m soil depth profile of potato (P) and barley (B) grown in the San Luis Valley. Regression line for the barley growing period (Line B) is y = 9.55 + 0.94x (r² = 0.75, significant at P < 0.01). The potato growing period has an equation as follows (Line P): y = 53.8 + 0.70x (r² = 0.79, significant at P < 0.01). The regression equation for the whole data set P and B (line not shown) is y = 17.7 + 0.90x (r² = 0.90, significant at P < 0.001)