IMPLICATIONS OF NITROGEN MANAGEMENT STRATEGIES FOR NITRATE LEACHING POTENTIAL - ROLES OF NITROGEN-SOURCE AND FERTILIZER RECOMMENDATION SYSTEM

Using the soil-based pre-sidedress nitrate test (PSNT) rather than the yield-goal-based cropping and manure history (CMH) to recommend N for corn (Zea mays L.) frequently results in less N applied. Our objectives were (i) to determine if this reduction in N application substantially reduces the potential for N leaching and (ii) to compare dairy manure and commercial fertilizer as N sources, both within PSNT-based systems. The 4-yr field study included (i) a control (no manure or N fertilizer), and three N fertilizer rates based on (ii) PSNT, no manure added (PSNT-M); (iii) cropping and manure history (CMH), no manure added; and (iv) dairy manure application with additional sidedress N if recommended by the PSNT (PSNT+M). The PSNT-M treatment received 112 kg N ha(-1) in 1990 and 123 kg N ha(-1) in subsequent years, while the CMH treatment received 168 kg N ha(-1) in all 4 yr. Corn yield, N uptake (defined as net aboveground N accumulation), spring and fall soil NO3- levels, and overwinter NO3-N losses were measured. Silage yields of PSNT+M generally were greatest (average of 16.5 Mg ha(-1)), followed by PSNT-M and CMH treatments, which were similar (14.8 Mg ha(-1)). The CMH system resulted in the highest soil NO3-N levels (to 120 cm) at harvest and greatest overwinter net profile NO3-N loss (average 66 kg ha(-1)). The results indicate (i) a reduced residual N after harvest and therefore reduced potential for N leaching when using the PSNT for N recommendations and (ii) similar or higher yields using manure compared with commercial fertilizer.