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United States Department of Agriculture

Agricultural Research Service


Location: Contaminant Fate and Transport Research

2013 Annual Report

1a. Objectives (from AD-416):
Conduct research to develop new and improved methods to manage pesticides and other organic agricultural chemicals to maintain healthy agricultural systems. Study the fate and transport of agricultural chemicals and investigate the effect of various soil and environmental processes that affect chemical movement in soil. Conduct research that provides "real-world" solutions to improve efficacy, reduce cost and foster a healthy environment. Develop new low-cost management approaches that minimize volatile emissions to the atmosphere, and transport to surface water and ground water.

1b. Approach (from AD-416):
An experimental site will be developed in Field 2B (UC-Riverside AgOps) to test the effectiveness of using solar heat pulsing to sterilize soils in preparation for planting various specialty crops. The experimental design will include standard 40” raised beds and have a bare-soil control and three solarization treatments with three replicates. Soil temperatures and heat flux throughout the raised-bed will be measured for several weeks. Various meteorological measurements will be made to allow determination of the solar energy input to the experiment. Several plant pests will be placed in the beds, be subjected to solarization for 4-6 weeks and then assayed for survival. After the solarization period, the plots will be fumigated with approximately 40% and 70% of the standard rate of Telone Inline to determine if pest control improvement occurs. The experiment will also include a negative control (no solarization, no fumigation) and standard fumigation treatments. Once the data is available, a modeling study will be conducted to investigate the heat transport and fate and transport of fumigant chemicals in the soil beds. Formerly 5310-12130-008-04S (11/10).

3. Progress Report:
This research is related to objective 2 of the parent project, "Develop and test new management practices to reduce contamination while controlling plant pests in strawberry and vegetable production". Research was completed for all objectives, which fall under National Program 212, Component 1. Enable Improvements of Air Quality via Management and Mitigation of Emissions from Agricultural Operations. Research on this project focused on Problem Statement 1A: Understand, predict, and manage emissions from agricultural systems. All proposed experiments, data analysis and mathematical modeling were completed during FY2012. During FY2013, the final report was completed. A summary of the project follows. Research was conducted to determine the effect of adding Ca(OH)2, K2CO3 and NH3 to soil on methyl bromide (MeBr) emissions. Ammonia was found to rapidly degrade MeBr (half-life was 2.5 hours) in a 1.0 M ammonia water solution compared to typical soil degradation (7-15 day half-life). Ammonia concentration of 0.10 M reduced the half-life to 8.5 hours and an ammonia amendment in moist soil was also found to promote MeBr transformation. A concentrated ammonia solution was found to effectively degrade MeBr under plastic film. Using a virtually permeable film, over 99.5% of the MeBr was destroyed by an ammonia-water solution in 8 hours. Based on these results, a new management practice was developed for using MeBr as a soil fumigant without significant emissions, i.e., for critical use exemption (CUE) purposes. A new soil heating method was conceived and tested, termed active solarization, to increase soil temperature and heating depth in the root zone. An experiment was conducted to compare heating for bare soil, standard (i.e., passive) solarization and active solarization methodologies. A cumulative heat stress index was used to determine th effect on plant–pest survival. After 15 days of heating, passive solarization increased CHT30 at 10 and 20 cm depths by 263 and 65 oC h, respectively, compared to leaving the soil bare. For active solarization, CHT30 increased, respectively, 387 and 105 oC h compared to bare soil. After 30 days of passive solarization, CHT30 at 10 and 20 cm was 345 and 66 oC h, respectively, and for active solarization CHT30, was 755 and 252 oC h. The results indicate that active solarization increases soil temperatures and heat stress on plant pests. Based on published pest survival information, observed CHT30 after active solarization would provide better control of a plant pest (nematode) compared to passive solarization. Active solarization may offer a suitable non-chemical alternative to soil fumigation and may help growers in areas where restrictive regulations on soil fumigation are being adopted. A field-plot study was conducted to determine the combined effects of reduced-rate fumigation and soil solarization on the control of soil-borne pests under typical field conditions. Using a drip irrigation system, a reduced-rate (i.e., 70% or 40%) of Telone Inline (a mixture of 1, 3-dichloropropene and chloropicrin) was applied to raised soil beds and covered with standard high-density polyethylene film (HDPE), thermic film (Thermic), and a virtually impermeable film (VIF). The spatial and temporal variation in the soil fumigant concentration was measured to determine the concentration-time index, which is a measurement of exposure to the fumigant and can be related to the control of plant pests and diseases. The efficacy of pest control of various treatments was monitored using bioassay muslin bags containing soil infested with citrus nematodes (Tylenchulus semipenetrans). The results show that standard HDPE together with reduced-rate of Inline controlled more than 50% of nematodes. Compared to the standard HDPE treatment, soil solarization with Thermic and VIF films coupled with reduced-rate of Inline improved efficacy of parasitic nematodes in soils because of the synergetic effect of fumigant and enhanced soil temperature. Due to the low permeability of VIF, the greatest fumigant concentrations in soil were observed which led to nearly full control of nematodes in the soil. The information obtained from this study will be useful in developing new soil disinfestation methods that reduce reliance on fumigants and are more environmentally benign. An experiment was conducted to determine the effects of agricultural films (e.g., tarps) on atmospheric emissions of soil fumigants, the distribution of fumigant in soil, and plant pathogen control in the field using plastic films with varying permeability and thermal properties. A reduced-rate of 70 % Telone Inline (61% 1,3-dichloropropene and 33% chloropicrin) was applied via drip irrigation to raised soil beds covered with standard high-density polyethylene film (HDPE), thermic film (Thermic), or virtually impermeable film (VIF). Fumigant emission rates were determined using dynamic flux chambers and the concentrations in soil were measured using a gas sampler. The pest control efficacy for the three treatments was determined using bioassay muslin bags containing soil infested with citrus nematodes (Tylenchulus semipenetrans). The results show that the Thermic treatment had the highest emission rates, followed by the HDPE and VIF treatments and the soil concentrations followed the reverse order. In terms of pest control, covering the beds with Thermic film led to sufficient and improved efficacy against citrus nematodes compared to standard HDPE film. For the HDPE treatment, more than 20% of nematodes survived in the soil at 30 cm depth. The VIF treatment substantially reduced the emission loss (2% of the Thermic and 6 % of the HDPE treatments) and eliminated plant parasitic nematodes because of its superior ability to entrap fumigant and heat within soils. The findings imply that not only the film permeability but the synergistic ability to entrap heat should be considered when developing new improved films for fumigation.

4. Accomplishments

Last Modified: 08/20/2017
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