Modeling nitrous oxide emissions from rough fescue grassland soils subjected to long-term grazing of different intensities using the Soil and Water Assessment Tool (SWAT)

Abstract

Given the rising nitrous oxide (NO) concentration in the atmosphere, it has become increasingly important to identify hot spots and hot moments of NO emissions. With field measurements often failing to capture the spatiotemporal dynamics of NO emissions, estimating them with modeling tools has become an attractive alternative. Therefore, we incorporated several semi-empirical equations to estimate NO emissions with the Soil and Water Assessment Tool from nitrification and denitrification processes in soil. We then used the model to simulate soil moisture and the NO flux from grassland soils subjected to long-term grazing (> 60 years) at different intensities in Alberta, Canada. Sensitivity analysis showed that parameters controlling the NO flux from nitrification were most sensitive. On average, the accuracy of NO emission simulations were found to be satisfactory, as indicated by the selected goodness-of-fit statistics and predictive uncertainty band, while the model simulated the soil moisture with slightly higher accuracy. As expected, emissions were higher from the plots with greater grazing intensity. Scenario analysis showed that the NO emissions with the recommended fertilizer rate would dominate the emissions from the projected wetter and warmer future. The combined effects of fertilization and wetter and warmer climate scenarios would increase the current NO emission levels by more than sixfold, which would be comparable to current emission levels from agricultural soils in similar regions.

Predicting nitrous oxide emissions after the application of solid manure to grassland in the United Kingdom

“…Although the model considers both nitrification and denitrification processes in its nitrogen cycle, the amount of N 2 O emitted during these processes is not explicitly reported in the original version of the model. Our current research work is in line with that of Shrestha, Thomas, Du, Hao, and Wang (), which incorporated several semiempirical equations from Parton et al. (), ) into the SWAT model.…”

“…It should be noted that the parameter for the maximum fraction of ammonium, K max , was .04–.05 (Table ) in the United Kingdom and .013–.03 in Canada (Shrestha et al., ). The small discrepancies were in a narrow range of .01–.05.…”

“…Calibration input ranges from Shrestha et al. () were used to run best fit parameters. The program generated different parameter sets from the specified range of values using the Latin hypercube sampling technique, which were regressed against the selected objective function.…”

Global soil nitrous oxide emissions since the preindustrial era estimated by an ensemble of terrestrial biosphere models: Magnitude, attribution, and uncertainty

“…Pasture and rangeland (grassland used for grazing animals) emit sizeable N 2 O gas from livestock excreta deposition, manure, and mineral fertilizer application (Davidson, ; Steinfeld, Gerber, Wassenaar, Castel, & DeHaan, ). Although some models such as DNDC (Giltrap & Ausseil, ; Li, Frolking, & Frolking, ; Saggar et al, ), the daily version of the CENTURY ecosystem model (DayCent; Abdalla et al, ; Del Grosso, Mosier, Parton, & Ojima, ; Parton, Hartman, Ojima, & Schimel, ), and the Soil and Water Assessment Tool (SWAT; Arnold et al, ; Shrestha, Thomas, Du, Hao, & Wang, ) simulated N 2 O emission from pasture soils, most global‐level model simulations have not considered the impacts of pasture management practices and livestock excreta deposition, which leads to the underestimation of soil N 2 O emissions from world’s grasslands (Dangal et al, In revision). The differences in model input datasets (such as climate data, land use and land cover, and N deposition) can be another important source of uncertainty in model simulations.…”

Effects of Grazing Management on Spatio-Temporal Heterogeneity of Soil Carbon and Greenhouse Gas Emissions of Grasslands and Rangelands: Monitoring, Modelling and Upscaling

“…Ehrhardt et al [73] questioned the use of model ensembles for upscaling projections of agricultural productivity and N2O emissions from field scale to larger spatial units due to soil spatial variability which is likely to reduce the accuracy of model projections. Current biogeochemical models usually do not differentiate the effects of grazing intensities on hydrological processes [84][85] due to lacking representation of terrain morphology and lateral flows, which often creates a great challenge to the prediction of future feedbacks among the grazing intensity, sediment, nutrient runoff and the C and N cycle.…”