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.