Fig. 4. Nitrate concentrations in the treated subbasin (TR1) minus the concentrations in the control subbasin (CN1) during the late spring nitrate test (LSNT) treatment period and the fitted quadratic model with a Lag 1 residual component and its 95% confidence limits. Concentrations from the two subbasins are significantly different when the confidence limits do not include the 0 difference line.