2013 Annual Report
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.