title: Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall and spring application of nitrogen and nitrapyrin.
abstract: Substantial amounts of NO3 from agricultural crop production systems on poorly drained soils can be transported to surface water via subsurface drainage. A field study was conducted from the fall of 1993 through 2000 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of fall vs. spring application of N and nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO3 losses from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments (fall N, fall N + NP, spring preplant N, and spring N + NP) were replicated four times and applied at 135 kg N ha(-1) for corn on individual drainage plots. Drainage occurred in all seven years. Seventy-one percent of the annual drainage and 75% of the annual NO3 loss occurred in April, May, and June. Fifty-four percent of the NO3 lost in the drainage occurred during the corn phase and 46% during the soybean phase. Annual flow-weighted NO3-N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L(-1) during the corn phase but annual NO3-N concentrations were still > or =10 mg L(-1) in three of six years for the spring preplant treatment. Averaged across the six rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > spring N + NP > fall N + NP > spring N. Under these conditions, NO3 losses in subsurface drainage from a corn-soybean rotation can be reduced 14% by spring N and 10% by late fall N + NP compared with fall-applied N. Nitrate losses were not appreciably reduced by adding NP to spring preplant N.
authors.affiliation: University of Minnesota Southern Research and Outreach Center, 35838 120th Street, Waseca, MN 56093-4521, USA. grandall@umn.edu
authors.forename: G W
authors.initials: GW
authors.lastname: Randall
authors.forename: J A
authors.initials: JA
authors.lastname: Vetsch
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D005308:Fertilizers; D009566:Nitrates / Q000032:analysis*; D009584:Nitrogen; D010847:Picolines; D012621:Seasons; D012989:Soil Pollutants / Q000032:analysis*; D013025:Glycine max; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*; D003313:Zea mays
chemical_list: D005308:Fertilizers; D009566:Nitrates; D010847:Picolines; D012989:Soil Pollutants; D014873:Water Pollutants; C017560:nitrapyrin; D009584:Nitrogen