A Review of Ongoing Advancements in Soil and Water Assessment Tool (SWAT) for Nitrous Oxide (N2o) Modeling

Abstract

Crops can uptake only a fraction of nitrogen from nitrogenous fertilizer, while losing the remainder through volatilization, leaching, immobilization and emissions from soils. The emissions of nitrogen in the form of nitrous oxide (N2O) have a strong potency for global warming and depletion of stratospheric ozone. N2O gets released due to nitrification and denitrification processes, which are aided by different environmental, management and soil variables. In recent years, researchers have focused on understanding and simulating the N2O emission processes from agricultural farms and/or watersheds by using process-based models like Daily CENTURY (DAYCENT), Denitrification-Decomposition (DNDC) and Soil and Water Assessment Tool (SWAT). While the former two have been predominantly used in understanding the science of N2O emission and its execution within the model structure, as visible from a multitude of research articles summarizing their strengths and limitations, the later one is relatively unexplored. The SWAT is a promising candidate for modeling N2O emission, as it includes variables and processes that are widely reported in the literature as controlling N2O fluxes from soil, including nitrification and denitrification. SWAT also includes three-dimensional lateral movement of water within the soil, like in real-world conditions, unlike the two-dimensional biogeochemical models mentioned above. This article aims to summarize the N2O emission processes, variables affecting N2O emission and recent advances in N2O emission modeling techniques in SWAT, while discussing their applications, strengths, limitations and further recommendations.

Factors That Influence Nitrous Oxide Emissions from Agricultural Soils as Well as Their Representation in Simulation Models: A Review

“…Table 5 summarizes these three models in simulating N 2 O emissions from managed soils, specifically in terms of the input data required for the model, the model components, processes and the impact factors that are considered in each model [25,30,168,173]. For the SWAT model, we also include the current SWAT N 2 O submodules, which are reviewed in Ghimire et al [28]. We programmed the main equations responsible for N 2 O emissions in the models DAYCENT, DNDC and SWAT using "R" programming language to plot and visualize the differences of the representation of each environmental factor on N 2 O.…”

“…These measurement factors are particularly important to contribute to the process of understandingN 2 O emissions and hence how they are represented in simulation models. Factors related to nitrification and denitrification processes have been reviewed by Cameron et al [26], Oertel et al [27], Signor et al [17] and Ghimire et al [28], while Saggar et al [29] reviewed factors impacting denitrification and the N 2 /N 2 O ratio.…”

Effects of winter pulsed warming and snowmelt on soil nitrogen cycling in agricultural soils: A lysimeter study

“…In temperate agroecosystems, soil freezing and thawing during the winter and shoulder seasons (late fall and early spring) is an important control on N 2 O emissions, and it is estimated 35-65% of annual N 2 O emissions (Wagner-Riddle et al, 1997;Wagner-Riddle et al, 2007;Risk et al, 2013;Wagner-Riddle et al, 2017) and around 80% of N leaching losses (Jayasundara et al, 2007) ) and NO 3 − in the soil coupled with decreased plant N uptake, which suggests that N is being lost due to NO 3 − leaching and N 2 O release (Campbell et al, 2014). The environmental controls on these freeze-thawinduced N 2 O emissions, the relative contributions of nitrification versus denitrification, and the contributions by N 2 O accumulated in the frozen soil versus N 2 O produced in situ upon thaw, have still not been fully resolved (Risk et al, 2014;Brin et al, 2018;Congreves et al, 2018;Ghimire et al, 2020). In this study, four lysimeter systems were used to determine the impact of winter warming and FTCs on N cycling in agricultural soils, comparing the impact on two soil textures, loamy sand and silt loam.…”

N2O Emissions from Two Austrian Agricultural Catchments Simulated with an N2O Submodule Developed for the SWAT Model

“…For a detailed description of these as well as their limitations see Wang et al [12]. For example, the DAYCENT (Daily Century) and the DNDC (DeNitrification-DeComposition) models are two commonly used physically based, biogeochemical models that simulate N2O emissions at the plot or the field scale [17,18], and the SWAT (Soil and Water Assessment Tool) model can be used to simulate N2O emissions at the catchment scale [19][20][21][22][23][24][25].…”

“…In SWAT, nitrification is a function of soil temperature and soil moisture, while denitrification is a function of soil moisture, temperature, SOC, and soil NO3 − [29]. A few studies have been undertaken to develop a SWAT N2O submodule to partition N2O emissions from the SWAT simulated nitrification and denitrification [20][21][22][23][24][25]. All the submodules use different approaches and equations.…”