HR: 0800h
AN: H51B-1116    [Abstracts]
TI: A Nitrogen Budget Model as an Indicator Of Leachable Nitrogen Under Agricultural Catchments
AU: * Burkart, M R
EM: burkart@nstl.gov
AF: National Soil Tilth Laboratory, USDA-ARS 2150 Pammel Drive, Ames, IA 50011 United States
AU: James, D E
EM: james@natl.gov
AF: National Soil Tilth Laboratory, USDA-ARS 2150 Pammel Drive, Ames, IA 50011 United States
AU: Liebman, M Z
EM: mliebman@iastate.edu
AF: Department of Agronomy, 3405 Agronomy Hall Iowa State University, Ames, IA 50011 United States
AU: van Ouwerkerk, E N
EM: evo@iastate.edu
AF: Department of Agricultural and Biosystems Engineering, 3112 NSRIC Iowa State University, Ames, IA 50011 United States
AB: Surplus nitrogen (N) in ground and surface water is of concern to land users and downstream water users in intensive agricultural regions. Surplus N is available for leaching during lengthy periods without crop cover in annual crop systems used in many temperate regions. This paper presents a model to estimate surplus N available for leaching to ground water beneath agricultural systems and demonstrates an application to catchments in western Iowa where the landscape is intensively managed for maize and soybean production. Biochemical processes of N transfer and transformation within agricultural systems are simulated. Stocks of N in soil, crops, and livestock, and external stocks representing fertilizer and the atmosphere are linked using commonly available georeferenced data on soils, crops, livestock, and inorganic fertilizer, making it applicable to catchments and watersheds in many regions. Atmospheric exchanges include volatilization from fertilizer, soil, manure, and senescing crops, denitrification, atmospheric deposition, and symbiotic fixation. Nitrogen flow is centered on exchange between the soil inorganic and organic N stock. Differential N mineralization rates are defined for three soil organic matter pools, crop residue, and manure based on carbon:N ratios. Nitrogen exports from the system are accounted for by quantifying harvested crops and animals in addition to losses to the atmosphere. Application of the model to contiguous watersheds produced watershed-averaged annual surpluses of 7 to 26 kg-N ha-1. Annual nitrate loads in local streams are 17 to 30 kg-N ha-1. Net losses of soil organic N are sufficiently small to suggest that the maize-soybean rotation is in near equilibrium with the soils of the region.
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1851 Plant ecology
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting