title: Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of nitrapyrin.
abstract: Subsurface drainage, a water management practice used to remove excess water from poorly drained soils, can transport substantial amounts of NO3 from agricultural crop production systems to surface waters. A field study was conducted from the fall of 1986 through 1994 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of time of N application and use of 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 split N (40% preplant and 60% sidedress)] were replicated four times and applied at 150 kg N ha(-1) for corn on individual drainage plots. Sixty-two percent of the annual drainage and 69% of the annual NO3 loss occurred in April, May, and June. Flow-weighted NO3-N concentrations in the drainage water were two to three times greater in the two years following the three-year dry period compared with preceding and succeeding years. Nitrate N concentrations and losses in the drainage from corn were greatest for fall N with little difference among the other three N treatments. Nitrate losses from soybean were affected more by residual soil NO3 following corn than by the N treatments per se. Averaged across the four rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > split N > spring N = fall N + NP. Under these conditions NO3 losses from a corn-soybean rotation into subsurface drainage can be reduced by 13 to 18% by either applying N in the spring or using NP with late fall-applied ammonia.
authors.affiliation: University of Minnesota Southern Research and Outreach Center, 35838 120th Street, Waseca, MN 56093-4521, USA. grandall@soils.umn.edu
authors.forename: G W
authors.initials: GW
authors.lastname: Randall
authors.forename: J A
authors.initials: JA
authors.lastname: Vetsch
authors.forename: J R
authors.initials: JR
authors.lastname: Huffman
mesh_terms: D000383:Agriculture; D005308:Fertilizers; D009566:Nitrates / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis*; D010847:Picolines / Q000737:chemistry*; D013025:Glycine max; D014872:Water Movements; D014876:Water Pollution / Q000517:prevention & control; D003313:Zea mays
chemical_list: D005308:Fertilizers; D009566:Nitrates; D010847:Picolines; C017560:nitrapyrin; D009584:Nitrogen