Tile Drainage Nitrate Concentrations in Response to Fertilizer Nitrogen Application

To elucidate the impact of the rate and timing of maize (Zea mays) fertilizer N practices upon surface water quality, a 14 ha field site was subdivided into six equal parcels of approximately 2.1 ha. Within each 2.1 ha parcel, 10.2 cm plastic drainage tile was installed on a 22.9 m grid with a single interceptor access point to collect tile drainage water on a weekly basis for nitrate-N (NO<SUB>3</SUB>-N) concentration. The field site contained uniform soil (Strawn-Mayville-Birkbeck Association), with 2 to 4% slope, soil pH of 5.5 to 6 and organic matter content of 3 to 4%. Six agricultural fertilizer N practices for maize were evaluated; 196 kg ha<SUP>–</SUP><SUP>1</SUP> fall-applied anhydrous ammonia with and without nitrapyrin (a commercially available nitrification inhibitor), 196 kg ha<SUP>–</SUP><SUP>1</SUP> pre-plant spring anhydrous ammonia, 140 kg ha<SUP>–</SUP><SUP>1</SUP> pre-plant spring anhydrous ammonia with nitrapyrin, 157 kg ha<SUP>–</SUP><SUP>1</SUP> sidedressed (post-planting) anhydrous ammonia and zero-rate control. Soybean was grown during the 1997, 1999, 2001 and 2003 growing seasons. Maize was grown during the 1998, 2000, 2002 and 2004 growing seasons. In general, the application of a full rate of anhydrous ammonia in the spring produced equivalent grain yields to that of the fall-applied N treatments, with decreased NO<SUB>3</SUB>-N release into tile drainage water. This reduction could be related to a tendency for increased plant N accumulation of the spring-applied N treatments and the shortened exposure time of the fertilizer N to loss. Based on the results from this study, producers within humid watersheds should apply N fertilizers in the spring before maize planting to minimize the loss of NO<SUB>3</SUB>-N into tile drainage systems, while optimizing grain yield and productivity.