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Research Project: Predicting and Reducing Agricultural Contaminants in Soil, Water, and Air

Location: Agricultural Water Efficiency and Salinity Research

Project Number: 2036-12130-011-00-D
Project Type: In-House Appropriated

Start Date: Jan 3, 2017
End Date: Jan 2, 2022

The overarching goal of this 5-year research plan is improving the understanding of the soil and environmental factors and agricultural practices that influence the fate, transport and emissions of pesticides in agricultural systems. This will be accomplished by developing new information related to soil mechanisms and their interactions, quantifying environmental factors that significantly affect fate and transport, and in developing a more accurate predictive model. Two objectives have been assigned to this project. Objective 1: Quantify mechanisms and processes that affect exchange of agricultural contaminants between soil, water, and air. Objective 1A. Obtain transport, transformation and partitioning coefficients for 1,3-dichloropropene (1,3-D) that can be used in predicting fate and transport. Objective 1B. Obtain information on initial chloropicrin concentration and soil degradation rate and develop a mathematical relationship to describe this process. Objective 1C. Test and verify the concentration-dependent soil degradation relationship using a radial-diffusion laboratory experiment. Objective 2: Develop and test a comprehensive contaminant fate and transport model that focuses on improved prediction of off-site movement (with an emphasis on volatilization).

Research will be conducted to: Objective 1A: Obtain basic information on vapor sorption, solubility, degradation, and Henry’s Law appropriate for the soil types and environmental conditions observed during the five 1,3-D field experiments. Develop relationships with soil type, soil water content, temperature and initial concentration that can be used for modeling activities described in Objective 2. Laboratory experiments will be conducted to measure the 1,3-D vapor density, degradation rate and adsorption in soil. These experiments will be conducted at 3 to 4 temperatures in the range 10 to 45 degrees Celsius. The soil vapor density measurements will be obtained at several water contents, including very dry soils. The effect of temperature on these transport parameters will be described using the Arrhenius equation. Objective 1B: Conduct laboratory column experiments to reveal the effect of initial chloropicrin concentration on emissions and degradation in soil and develop a mathematical relationship describing this process. Soil degradation will be measured in laboratory incubation experiments (see Obj 1A) and in triplicated soil column experiments. The columns will be housed in a controlled temperature room at 25 degrees Celsius. Seven field application rates will be tested (50 to 350 lbs/acre) using native soil. Experiments will also be conducted using sterilized soil at two or three field application rates (e.g., 100, 200, and 300 lbs/acre). A model of the concentration-dependence of the degradation rate will be obtained using a logistic-response model, by fitting the initial concentrations and degradation rates. Objective 1C: Test and verify the concentration-dependent soil degradation relationship by conducting a radial-diffusion laboratory experiment. Use soil degradation rates obtained in laboratory incubation experiments to parameterize concentration-dependent degradation in a 2-D numerical transport model and determine if the model more accurately predicts the radial diffusion within the 2-D soil monolith. CHAIN-2D, or similar, will be modified to enable simulation of a concentration-dependent degradation process and used to predict the soil concentrations and emissions in the 2-D soil monolith. Numerical predictions using constant degradation rates will be compared to predictions using concentration-dependent rates to determine if the concentration-dependent model performs better. Objective 2: Develop and test a comprehensive contaminant fate and transport model that focuses on improved prediction of volatilization. Show that soil drying and vapor adsorption controls the timing of the peak fumigant emission rate during daily (i.e., 24 h) periods by comparing measured 1,3-D emission rates to predicted emission rates using a fully coupled heat, water, water vapor and chemical transport model coupled to atmospheric processes. Model accuracy will be determined by comparing field emission measurements and model predictions of soil temperature, soil water content, emissions, and timing of peak emission rates.