HR: 0800h
AN: B31A-0058    [Abstracts]
TI: Nitrogen Cycle Modeling: a Mechanistic Estimate of N-losses From Agricultural Fields Over the Seasonal Time Period
AU: * Maggi, F
EM: fmaggi@berkeley.edu
AF: Berkeley Water Center, University of California, Berkeley, 413 O'Brien Hall, Berkeley, ca 94720,
AU: Gu, C
EM: cgu@berkeley.edu
AF: Berkeley Water Center, University of California, Berkeley, 413 O'Brien Hall, Berkeley, ca 94720,
AU: Venterea, R
EM: venterea@umn.edu
AF: Soil and Water Management Research Unit, USDA-Agricultural Research Service, 439 Borlaug Hall, 1991 Upper Buford Circle, St. Paul, MN 55108,
AU: Riley, W
EM: wjriley@lbl.gov
AF: Lawrence Berkeley National Laboratory, Earth Science Division, One Cyclotrone rd., Berkeley, CA 94720,
AU: Oldenburg, C
EM: cmoldenburg@lbl.gov
AF: Lawrence Berkeley National Laboratory, Earth Science Division, One Cyclotrone rd., Berkeley, CA 94720,
AB: The biogeochemical cycle of nitrogen and production of NO, N2O, and CO2 gas and NO2- and NO3- ions in nutrient-enriched agricultural fields is mediated by soil microbial activity, the hydrological cycle, plant dynamics, and climatic forcing. Understanding how NO, N2O, CO2 gases and NO2- and NO3- ions are released from agricultural fields to the environment is a key factor in controlling the green-house effect and water contamination, and assumes ever greater importance in view of the foreseen increase in biofuel, food, and fiber production. To address these issues we have developed a mechanistic model (TOUGHREACT-N) for various nitrification and denitrification pathways, multiple microbial biomass dynamics, heat and water flows, and various chemical reactions at local and kinetic equilibrium. The soil column is represented in a 1D framework, with hydraulic properties described by a water tension-saturation model. Biotic and abiotic reactions are assumed to follow Michaelis-Menten kinetics, while a consortium of several micro-organismal strains is assumed to follow multiple Monod growth kinetics accounting for electron donor, electron acceptor, and inhibitor concentrations. Water flow is modeled with the Darcy-Richards equation, while nutrient transport is modeled by Fickian advective and diffusive processes in both gaseous and liquid phases. Heat flow is modeled with the Fourier equation. Plant dynamics is taken into account by coupling TOUGHREACT-N with CERES to determine water and nutrient uptake, and soil carbon accumulation. TOUGHREACT-N was calibrated against field measurements to assess pathways of N losses following fertilization. A good agreement between field observations and model predictions was found. We identified two dominant time scales in the system response that depended on plants dynamics. Before plants have substantial impact on soil nutrients and moisture content, N losses are characterized by rapid increases as a function of water application rate and fertilizer amount and application depth. Under reference fertilization and irrigation practices, approximately 1.64% and 1.61% of the total applied N is lost as N-NO(g) and N-N2O(g), respectively, while losses of N-N2(g), N-NO2-, and N-NO3- where several orders of magnitude smaller. When plants grow, pulses in N losses became smoother due to nutrient and water uptake. Contrarily to predictions of non- mechanistic, coarse-scale models (e.g., CASA, CENTURY) N losses are predominantly non-linearly increasing with fertilizer and water application amount, and with fertilizer application depth, thus invoking a revision of long- term estimates of nitrogen and carbon balances at global scales
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0469 Nitrogen cycling
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting