title: Use of N immobilization to tighten the N cycle in conventional agroecosystems.
abstract: Soils in conventional agroecosystems are purposely held in a nitrogen (N)-saturated state to maximize crop yields. Planting winter annual cover crops when fields are usually fallow has been proposed to ameliorate N losses from soils. In this study we introduced winter annual cover crops into an N rate study with plots fertilized at 0, 34, 67, 101, 134, 168, and 202 kg N/ha in maize (Zea mays L.) to determine how winter annual cover crops affect yields, N2O and NO3- fluxes, and N pools. At the six-leaf stage and during flowering, incorporation of cover crop into soil resulted in a 30% reduction in maize biomass. Three weeks after fertilization, KCl-extractable soil mineral N was 75-87% lower in covercropped soils than in no-cover soils, indicating that N had been immobilized in the covercropped soils. At physiological maturity, there was no difference between cover and no-cover treatments in crop yield, which was maximized at 9 Mg/ha in 2006 and 7 Mg/ha in 2007. Where N rates exceed crop requirements, cover crop incorporation may reduce N exports as NO3- and N2O. Tighter N cycling in conventional agroecosystems could be fostered by matching N rates to the amount of N removed with grain and using N immobilization to retain N and support yields. If N immobilization is viewed as a means for efficient fertilizer N use rather than a process that decreases crop productivity, growers might be more willing to adopt cover-cropping practices.
authors.affiliation: W. K. Kellogg Biological Station, Michigan State University, 3700 East Gull Lake Drive, Hickory Corners, Michigan 49060, USA. mcswiney@kbs.msu.edu
authors.forename: Claire P
authors.initials: CP
authors.lastname: McSwiney
authors.forename: Sieglinde S
authors.initials: SS
authors.lastname: Snapp
authors.forename: Lowell E
authors.initials: LE
authors.lastname: Gentry
mesh_terms: D000383:Agriculture; D018533:Biomass; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D009609:Nitrous Oxide / Q000032:analysis; D012987:Soil / Q000032:analysis*; D014887:Weather; D003313:Zea mays / Q000378:metabolism*
chemical_list: D009566:Nitrates; D012987:Soil; D009609:Nitrous Oxide; D009584:Nitrogen