Nitrate Loss in Subsurface Drainage from a Corn-Soybean Rotation as Affected by Nitrogen Rate and Nitrapyrin.

Successful N management practices for the US Midwest must optimize crop production and minimize NO-N losses from subsurface tile drainage. The objective of this study was to measure the effects of N rate, N application timing, and nitrapyrin [2-chloro-6-(trichlormethyl) pyridine] on corn ( L.) production and NO-N in tile drainage water in a corn-soybean [ (L.) Merr.] rotation in Minnesota. Anhydrous ammonia was applied at 90 and 179 kg ha with nitrapyrin in the fall and at 134 kg ha with and without nitrapyrin in fall and spring. However, drainage water monitoring was only conducted on fall treatments. Over a 5-yr period, 71% of drainage occurred in April through June and <1% occurred from November through March due to frozen soil. Averaged across N treatments and crops, annual drainage ranged from 69 to 380 mm among years. From 2001 through 2003, NO-N concentrations averaged 13.8, 15.6, and 20.0 mg L in corn and 7.3, 8.2, and 12.6 mg L in soybean when 90, 134, and 179 kg N ha was fall applied with nitrapyrin to corn, respectively. Corn grain yields were greater with spring-applied N at 134 kg ha (11.3 Mg ha) than with fall-applied N at 134 and 179 kg ha with nitrapyrin (10.5 and 10.8 Mg ha, respectively), and nitrapyrin did not affect corn production or water quality. Fall application of N is common on cold soils in Minnesota. These data showed that fall application required a greater rate of N to optimize yield than spring and that greater fall rate often increased NO-N concentration and load in tile drainage water.

Fate of Salmonella following application of swine manure to tile-drained clay loam soil.

Land application of animal manure is an important means of utilization of nitrogen and phosphorus. However, the presence of pathogens in manure and their occasional leaching into subsurface water has become a topic of concern during the past few years. This study was undertaken to determine the extent to which Salmonella anatum may leach through tile-drained clay loam soil on which swine manure has been applied. For this purpose, swine manure was experimentally contaminated with S. anatum and applied to three tile-drained plots in winter of 2001 while another three plots served as negative controls. Following rainfall events in the spring of 2002 the tiles started to flow and leachate samples of subsurface water were collected at various time intervals and tested for S. anatum. Salmonella anatum was not found to leach into the subsurface drainage water indicating that it was either retained in the upper layers of soil or did not survive over winter. The leaching of faecal coliforms and coliphages was also tested. Faecal coliforms and coliphages were detected in the subsurface water from both manure and control plots, indicating the ability of the tile drainage system to transport these organisms to groundwater as the water percolates through the soil. Additional temporal studies over a longer time period are needed to determine the survival and leaching of pathogens and indicators into subsurface water.