Location: Contaminant Fate and Transport Research2013 Annual Report
1a. Objectives (from AD-416):
Objective 1: Measure and model mechanisms and processes that affect exchange of pesticides between soil, water, plants and air; and that improve prediction of atmospheric emissions. Objective 1a. Conduct Laboratory Experiments and Modeling Studies to Test Accuracy of Simplified Approaches for Estimating Fumigant Emissions. Objective 1b. Determine the Effect of Fumigant Exposure and Soil Temperature on Survival of Nematodes, Fungi, and Weed Seeds. Objective 1c. Develop and Test a Model to Predict Fumigant Fate and Transport and Survival of Nematodes, Fungi, and Weed Seeds after Soil Fumigation. Objective 2: Develop and test new management practices to reduce contamination while controlling plant pests in strawberry and vegetable production.
1b. Approach (from AD-416):
Research will be conducted to 1) develop and test simple, low-cost, and accurate methods to obtain fumigant emissions estimates, primarily cumulative emissions. A series of laboratory chamber experiments and mathematical simulations of fumigant fate and transport will be conducted and compared directly to data collected from several field experiments completed during the previous research project. A direct comparison will be made between the existing field measurements of cumulative emissions and the results from the planned laboratory and simulation experiments. Agreement indicates that the simplified methodology provides equivalent information. 2) Laboratory incubation experiments will be conducted to obtain information on the relationship between concentration, temperature and exposure time on several important plant pest organisms (i.e., a nematode, fungi, and weed). 3) Experiments will be conducted and a mathematical model will be used to determine if the control of plant pests can be predicted after soil fumigation based on fumigant concentration and organism mortality relationships. 4) Experiments will be conducted to test a new pest-control approach that uses recirculated irrigation water and a solar collector to increase soil heating.
3. Progress Report:
Progress was made on all objectives. Under Objective 1A, we completed laboratory experiments measuring instantaneous and total emissions of drip applied soil fumigants in a 2-dimensional system. A mathematical model was used to compare measured and predicted emission rates from simulated shank injection. This research has demonstrated that useful information concerning emissions of soil fumigants can be obtained from laboratory column experiments conducted using simulated field temperature fluctuations. Furthermore, it was found that numerical simulations provided accurate estimates of total emissions. Therefore, complex, time consuming, and very expensive field experimentation is not always required to obtain useful data on total field-scale emissions rates. For Objective 1b, the data from field experiments conducted in FY2012 were analyzed to provide measurements of plant pest survival under fumigant and temperature stresses. Additional laboratory experiments of pest survival are needed for comparison to the field measurements. This will be completed early in FY2014. For Objective 1c, a comprehensive process-based mathematical model was developed to assess herbicide (i.e., diazinon) emissions to the atmosphere. The mathematical model allows simulation of the diurnal variation of pesticide volatilization as affected by soil-water content, the air-solid interface partitioning coefficient (i.e. vapor sorption), soil-water retention function and soil surface resistance processes which coupled soil-based processes to atmospheric conditions. The model was initially tested by conducting simulations of diazinon emissions for ten successive days of drying under typical semi-arid summer conditions following application to either a loam or sand soil. Results showed that the temporal variation and magnitude of diazinon emission were strongly affected by the air-solid interface partition coefficient, soil-water content and the surface resistance function. Additional testing involved comparison of model predictions and field measurement of diazinon emissions from Yolo silt loam soil from the San Joaquin Valley. In general, the model over predicted the emission rate but was able to describe a range of observed emission patterns: (a) for wet soil, the timing of emission peaks occurred during the afternoon, (b) for dry soil, the timing of the emission peaks occurred at night. This behavior cannot be predicted using traditional pesticide emission models. For Objective 2, a field experiment was completed and the data were analyzed to determine the effectiveness of combining soil heating and reduced application of soil fumigants for controlling soil pests and pathogens. The findings demonstrate that both the film permeability and entrapped heat synergistically affect soil organism survival and should be considered together when developing new improved fumigation methods.
Reichman, R., Yates, S.R., Skaggs, T.H., Rolston, D.E. 2013. Effects of soil moisture on the diurnal pattern of pesticide emission: Numerical simulation and sensitivity analysis. Atmospheric Environment. 66(2013):41-51.