The Pre‐Sidedress Soil Nitrate Test and Nitrate Leaching from Corn

The pre‐sidedress soil nitrate test (PSNT) is recommended in many states as a best management practice (BMP) for corn ( Zea mays L.). A 2‐yr study was conducted in Connecticut on a Woodbridge fine sandy loam soil (coarse loamy, mixed, mesic Aquic Dystrochrept) to determine NO 3 ‐N concentrations and losses in soil water from corn managed with three different N fertilization regimes: (i) PRE, 196 kg N ha −1 applied preplant; (ii) PSNT‐1, 90 kg N ha −1 applied at preplant and any remaining N needs estimated by the PSNT (0 kg ha −1 in 1995 and 45 kg ha −1 in 1996); and (iii) PSNT‐2, no preplant N and all N needs estimated by the PSNT (34 kg ha −1 in 1995 and 123 kg ha −1 in 1996). Percolate was collected with zero‐tension pan lysimeters. Flow‐weighted NO 3 ‐N concentrations from the PRE treatment were 22.3 mg L −1 in 1995 and 17.4 mg L −1 in 1996; the PSNT treatments were <8.0 mg L −1 . Losses of NO 3 ‐N as a percent of N applied in 1995 were 20%, 10%, and 12% for PRE, PSNT‐1, and PSNT‐2, respectively, and 31%, 21%, and 21%, respectively, in 1996. Greatest leaching losses occurred after corn harvest. Corn yields were not significantly (P > 0.05) different among N treatments. These findings suggest that a well calibrated soil N test can reduce excess fertilization and the potential for NO 3 contamination of ground water.