Location: Contaminant Fate and Transport Research2010 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. Replaces 5310-12130-008-00D (2/10).
3. Progress Report
(a) Laboratory and modeling studies are currently being conducted. The experiments use soil, environmental, fumigant management, and emission–reduction conditions that are similar to recent field experiments. Once the data has been collected and analyzed, a direct comparison will be made between the field measurements and the laboratory experiments. An existing finite difference numerical model has been modified to allow simulation of the fate and transport of a fumigant in the presence of ammonium thiosulfate. This required the addition of a second-order reaction mechanism. The program has been extensively tested and is ready for use in simulating the field and laboratory experiments. (b) Laboratory studies have begun to measure the survival of plant pests under temperature and chemical stress. (c) A preliminary study related to Objective 2 (Develop and test new management practices to reduce contamination while controlling plant pests in strawberry and vegetable production) was completed and demonstrates that active solarization produces higher soil temperatures than passive solarization. This study also provided information that will be used in designing the field experiment to combine solarization and reduces rate fumigation.
1. ACTIVE SOLARIZATION, A NON-CHEMICAL ALTERNATIVE TO SOIL FUMIGATION. Soil fumigants are important for agricultural production in semi-arid regions, but their high emission rates may negatively impact soil, water and air resources. Soil heating via solarization has been proposed as a non-chemical alternative to soil fumigation, but has not found wide acceptance due to limitations in soil temperatures and heating depth, especially in cooler environments. ARS scientists in Riverside, CA developed a new soil heating method has been developed (active solarization) to increase soil temperatures and heating depth in the root zone. An experiment was conducted to compare soil temperatures for bare soil, standard (i.e., passive) solarization and active solarization methodologies using a cumulative heat stress index that has been shown to be related to plant–pest survival. The results demonstrate that active solarization increases soil temperatures and heat stress on plant pests compared to traditional solarization. Based on published pest survival information and observed heat stress levels, we found that better control of a plant pest (nematode) was obtained using active solarization compared to passive solarization.
2. HYDROLYSIS AND PHOTOLYSIS OF OXYTETRACYCLINE IN WATER. Increasing attention has been paid to the environmental fate of veterinary antibiotics due to the occurrence of these chemicals in the environment. ARS scientists in Riverside, CA, investigated oxytetracycline degradation via hydrolysis and photolysis in this study, since large quantities of tetracycline antibiotics are administered to farm animals for therapeutic treatment and health protection. Oxytetracycline hydrolysis was found to follow first-order degradation kinetics with half-lives ranging from 6 – 7 days over a range of initial concentrations at 25 C, and much higher in solutions at neutral pH and higher temperatures. Oxytetracycline photolysis was rapid with a degradation half live of approximately 0.2 days suggesting that degradation via photolysis would dominate in a shallow water environment. This information will be valuable in protecting sensitive ecosystems and in developing new methods to reduce antibiotic loading to surface water.