Linking agricultural crop management and air quality models for regional to national-scale nitrogen assessments

Abstract

While nitrogen (N) is an essential element for life, human population growth and demands for energy, transportation and food can lead to excess nitrogen in the environment. A modeling framework is described and implemented, to promote a more integrated, process-based and system-level approach to the estimation of ammonia (NH<sub>3</sub>) emissions resulting from the application of inorganic nitrogen fertilizers to agricultural soils in the United States. The United States Department of Agriculture (USDA) Environmental Policy Integrated Climate (EPIC) model is used to simulate plant demand-driven fertilizer applications to commercial cropland throughout the continental US. This information is coupled with a process-based air quality model to produce continental-scale NH<sub>3</sub> emission estimates. Regional cropland NH<sub>3</sub> emissions are driven by the timing and amount of fertilizer applied, local meteorology, and ambient air concentrations. An evaluation of EPIC-simulated crop management activities associated with fertilizer application at planting compared with similar USDA state-level event estimates shows temporally progressive spatial patterns that agree well with one another. EPIC annual inorganic fertilizer application amounts also agree well with reported spatial patterns produced by others, but domain-wide the EPIC values are biased about 6 % low. Preliminary application of the integrated fertilizer application and air quality modeling system produces a modified geospatial pattern of seasonal NH<sub>3</sub> emissions that improves current simulations of observed atmospheric nitrate concentrations. This modeling framework provides a more dynamic, flexible, and spatially and temporally resolved estimate of NH<sub>3</sub> emissions than previous factor-based NH<sub>3</sub> inventories, and will facilitate evaluation of alternative nitrogen and air quality policy and adaptation strategies associated with future climate and land use changes

Evaluation of a regional air-quality model with bidirectional NH<sub>3</sub> exchange coupled to an agroecosystem model

“…The agricultural cropping activity data required are fertilizer application rates, depths, and timing. These variables are provided on a daily basis from CONUS EPIC simulations (Cooter et al, 2012). EPIC estimates of the NH + 4 content in applied fertilizers are used by CMAQ as an input to the soil NH + 4 pool.…”

“…A NH 3 bidirectional exchange model was developed for the CMAQ modeling system using field scale (∼ 100 ha) observations taken at field sites in North Carolina, USA , and published NH 3 air-surface exchange parameterizations (Massad et al, 2010 Cooter et al (2012), and g due to inorganic fertilization application was calculated following Massad et al (2010).…”

“…Fertilizer application rates, dates and methods, injected to 0.05 m or surface applied, for 21 major US crops were provided from a CONUS simulation of EPIC (Cooter et al, 2012). Unlike Massad et al (2010), who used an exponential decay function to adjust g as a function of time after fertilization, the atmosphere-soil NH + 4 budget was simulated in CMAQ as being dynamically coupled to hourly soil NH + 4 losses due to evasion and nitrification, and increases in soil NH 3 due to deposition.…”

“…The NEI fertilizer emissions were removed from the bidirectional case and fertilizer emissions were estimated dynamically within CMAQ using the EPIC agricultural management output. Information regarding inorganic fertilizer application amounts and timing were simulated for bidirectional CMAQ using EPIC (Williams, et al, 2008;Izaurralde et al, 2006) as described above and in Cooter et al (2012). The vegetation apoplastic emission potential, s , was parameterized as a function of the land cover type.…”

“…The growing of crops represents a large spatial area where the impact of agricultural management practices alters the balance of atmospheric NH 3 sources and sinks. This manuscript describes an analysis in which the Community Multiscale Air-Quality (CMAQ version 5.0) modeling system was modified to include bidirectional NH 3 exchange and coupled to a soil nitrogen model (Cooter et al, 2012) based on the routines in the United States Department of Agriculture's (USDA) Environmental Policy Integrated Climate (EPIC) agroecosystem model (Williams et al, 2008) for the US continental domain. The reduced nitrogen (NH x = NH 3 + NH + 4 ) wet deposition results of this coupled modeling system were evaluated against the National Atmospheric Deposition Program's (NADP) National Trends Network (NTN) NH x observations.…”