Estimating Field Volatility of Soil Fumigants Using CHAIN_2D: Mitigation Methods and Comparison Against Chloropicrin and 1,3-Dichloropropene Field Observations

Abstract

Academic, government, and industrial field researchers have generated a significant database of field studies of the volatility of soil applied fumigants. However, limited work exists in validating physical models against field volatility data sets and fully exploring the volatility parametric response surface. Field studies quantifying atmospheric flux for soil fumigants 1,3-dichloropropene and chloropicrin are validated against the United States Department of Agriculture (USDA Salinity Laboratory) soil physics model CHAIN_2D that was modified specifically for agronomic uses of soil fumigants. Comparison between model predictions and field observations for six unique field trials in five different states indicate that CHAIN_2D effectively captures the magnitude and duration of fumigant emission from soil observed experimentally with r 2 ∼0.14-0.96 (avg. 0.66) for peak emission, and r 2 ∼0.76-1.0 (avg. 0.91) for cumulative emissions (r equals the Pearson moment correlation coefficient). Correct prediction magnitudes suggest that CHAIN_2D is a useful tool for extrapolating flux predictions to diverse scenarios not addressed by field trials. Examples of mitigation strategies such as the use of agricultural films (tarps), increased soil injection depth, and management of soil water content, under near semiinfinite parameter combinations of soil, meteorological, and agronomic properties are discussed.

Soil Fate of Agricultural Fumigants in Raised-Bed, Plasticulture Systems in the Southeastern United States

“…Previously, studies have been initiated to model fumigant soil flux and atmospheric emissions over large areas using methods and conditions representative of commercial production practices (Cryer and Wesenbeeck, 2009; Li et al, 2006). However, corresponding data documenting the fate of fumigants in soil when applications were made under GAPs are lacking, most notably when applications are made over large areas using methods and conditions representative of commercial production practices.…”

Coupling Field Observations, Soil Modeling, and Air Dispersion Algorithms to Estimate 1,3‐Dichloropropene and Chloropicrin Flux and Exposure

“…All peaks of the observed discrete flux (both in magnitude and timing postapplication) are captured by CHAIN_2D. Additional validation work for 1,3‐D and chloropicrin using CHAIN_2D is found elsewhere (Cryer and van Wesenbeeck, 2009).…”

“…Tarp splitting and removal at some time post‐application are typical practices for broadcast uses of chloropicrin, and these occurred at 133 and 157 h post‐application, respectively. Additional details and other trials for 1,3‐D and chloropricrin are found elsewhere (Cryer and van Wesenbeeck, 2009).…”

“…Historical fumigant research has focused on field and laboratory measurements, but more recently, numerical models have been used to predict fumigant volatilization. These include the two‐dimensional USDA models CHAIN_2D (Šimůnek and van Genuchten, 1994; Wang et al, 1998, 2000, 2007; Cryer and van Wesenbeeck, 2009) and HYDRUS (Šimůnek et al, 2008), the one‐dimensional models LEACHV (Chen et al, 1995) and PRZM (Carsel et al, 1985, 1995, Cryer et al, 2003), and linear approximations (Woodrow et al 2001, van Wesenbeeck et al, 2008). Fumigant or volatile organic chemical (VOC) loss from soil predicted by these models (or field measurement) can be specified as transient source terms in air dispersion modeling.…”

“…Field studies cannot address the impact of agronomic practices, soil type, and meteorological conditions on fumigant emissions when conditions differ from those seen experimentally, and thus the need for soil physics based models such as CHAIN_2D (Šimůnek and van Genuchten, 1994; Šimůnek et al, 2008). CHAIN_2D is a public domain model that solves saturated–unsaturated water flow (Richards’ equation) and the convection–dispersion equation for heat and solute (includes diffusion in the gaseous phase) transport and has been used to predict soil fumigant emissions from soil (Wang et al, 2000) and validated for several soil fumigants (Cryer and van Wesenbeeck, 2009).…”