Implications of Nitrogen Management Strategies for Nitrate Leaching Potential: Roles of Nitrogen Source and Fertilizer Recommendation System

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Abstract
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 NO‐3 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.

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