Chapter 18. DAYCENT Simulated Effects of Land Use and Climate on County Level N Loss Vectors in the USA

Authors

S. J. Del Grosso, USDA-ARS
W. J. Parton, Colorado State University
D. S. Ojima, Colorado State University
C. A. Keough, Colorado State University - Fort Collins
T. H. Riley, Colorado State University - Fort Collins
A. R. Mosier, Mount Pleasant, SC

Date of this Version

2008

Comments

Published in Nitrogen in the Environment: Sources, Problems, and Management, Second edition, ed. J. L. Hatfield & R. F. Follett (Amsterdam, Boston, et al.: Academic Press/Elsevier, 2008).

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United States Code, Title 17, §105.

Abstract

We describe the nitrogen (N) gas (NH₃, NO_x, N₂O, N₂) emission and NO₃ leaching submodels used in the DAYCENT ecosystem model and demonstrate the ability of DAYCENT to simulate observed N₂O emission and NO₃ leaching rates for various sites representing different climate regimes, soil types, and land uses. DAYCENT simulated seven major crops, grazing lands, and potential native vegetation at the county level for the United States. At the national scale, NO₃ leaching was the major loss vector, accounting for 86%, 66%, and 56% of total N losses for cropped soils, grazed lands, and native vegetation, respectively. NH₃ volatilization + NO_x emissions made up the majority of national N gas losses, accounting for 58%, 89%, and 86% of N gas losses from cropped soils, grazed lands, and native vegetation, respectively. However, there was considerable spatial variability in the N loss vectors, with leaching accounting for less than 20% of total N losses and NO_x + NH₃ emissions accounting for less than 50% of N gas losses in some counties. Land use area weighted mean annual N losses were 43.9 (SD = 26.8) and 12.3 (SD = 22.2)kg N/ha for cropped/grazed and native systems, respectively. Area weighted mean annual N gas losses were 11.8 (SD = 4.8) and 5.4 (SD = 2.1)kg N/ha for cropped/grazed and native systems, respectively. Total N losses and NO₃ leaching tended to increase as N inputs and precipitation increased, and as soils became coarser textured. Total N gas losses also increased with N inputs and as soils became coarser textured, but N₂O and N₂ made up a larger portion of N gas losses as soils became finer textured and as precipitation increased.