[Effects of chloropicrin fumigation on soil and growth and development of Panax notoginseng].

The continuous cropping obstacle of Panax notoginseng is serious, and effective control measures are lacking. Soil disinfection with chloropicrin(CP) has been proven to be effective in reducing the obstacles to continuous cropping of other crops. In order to ascertain the effect of CP in the continuous cropping of P. notoginseng, this paper explored the influences of CP at different treatment concentrations(0,30,40,50 kg/Mu, 1 Mu≈667 m~2) on soil macro-element nutrients, soil enzyme activity, growth and development of P. notoginseng, and the accumulation of medicinal components. The results showed that CP fumigation significantly increased the content of total nitrogen, alkali-hydrolyzable nitrogen, ammonium nitrogen, nitrate nitrogen, and available phosphorus in the soil, but it had no significant effect on potassium content. The soil protease activity showed a trend of first increasing and then decreasing with the prolonging of the treatment time. Both the soil urease and acid phosphatase activities showed a trend of first decreasing and then increasing with the prolonging of the treatment time. The higher the CP treatment concentration was, the lower the urease and acid phosphatase activities would be in the soil. The protease activity was relatively high after CP40 treatment, which was better than CP30 and CP50 treatments in promoting the nitrogen-phosphorus-potassium accumulation in P. notoginseng. The seedling survival rates after CP0, CP30, CP40, and CP50 tratments in October were 0, 65.56%, 89.44%, and 83.33%, respectively. Compared with the CP30 and CP50 treatments, CP40 treatment significantly facilitated the growth and development of P. notoginseng, the increase in fresh and dry weights, and the accumulation of root saponins. In summary, CP40 treatment accelerates the increase in soil nitrogen and phosphorus nutrients and their accumulation in P. notoginseng, elevates the seedling survival rate of P. notoginseng, enhances the growth and development of P. notoginseng, and promotes the accumulation of medicinal components. CP40 treatment is therefore recommended in production.

Effect of application rate on fumigant degradation in five agricultural soils.

Soil fumigation is an important pest management tool for many high value crops. To address the knowledge gap of how fumigant concentration in soil impacts dissipation, and thereby efficacy, this research determined the degradation characteristics of four fumigants as affected by application rate. Laboratory incubation experiments were conducted to determine degradation rates of 1,3-dichloropropene (both cis- and trans isomers), chloropicrin (CP), dimethyl disulfide (DMDS), and methyl iodide (MeI) in five agricultural soils. Fitted to pseudo first-order kinetics, the degradation rate constant (k) of CP, DMDS, and MeI decreased significantly as application rate increased while the 1,3-D isomers were the least affected by rate. Half-lives increased 12, 17, and 6-fold for CP, DMDS, and MeI, respectively, from the lowest to the highest application rate. At low application rates, the degradation rate of all fumigants in the Hueneme sandy loam soil was reduced by 50-95% in sterilized soil compared to the biologically active controls. However, this difference became much smaller or disappeared at high application rates indicating that biodegradation dominates at low concentrations but chemical degradation is more important at high concentrations. When co-applied, CP degradation was enhanced with biodegradation remained above 50%, while 1,3-D degradation was either reduced or not changed. Among the fumigants tested, the relative importance of biodegradation was DMDS>CP>MeI>1,3-D. These results are useful for determining effective fumigation rates and for informing regulatory decisions on emission controls under different fumigation scenarios.

Emissions from soil fumigation in two raised bed production systems tarped with low permeability films.

Raised beds are used to produce some high-value annual fruit and vegetable crops such as strawberry in California (CA) and tomato in Florida (FL), USA. Pre-plant soil fumigation is an important tool to control soil-borne pests in the raised beds. However, fumigant emissions have detrimental environmental consequences. Field trials were conducted to evaluate emissions of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) in two different production systems with raised beds covered by different tarps. In the CA trial, InLine (60.8% 1,3-D and 33.3% CP) was drip-applied at 340 kg ha(-1) to 5 cm deep in the beds (30 cm high and 107 cm wide) tarped with polyethylene (PE) or virtually impermeable film (VIF). In the FL trial, carbonated Telone C35 (63.4% 1,3-D and 34.7% CP) was shank-applied at 151 kg ha(-1) to 20 cm deep in the beds (22 cm high and 76 cm wide) tarped with totally impermeable film (TIF). Emissions from tarped beds relative to furrows were contrary between the two trials. For the CA trial, the emission was 47% of applied 1,3-D and 27% of applied CP from PE tarped beds and 31% of applied 1,3-D and 15% of applied CP from VIF tarped beds, while that from uncovered furrows was<0.4% for both chemicals in both fields. In the FL trial, only 0.1% 1,3-D was emitted from the TIF tarped beds, but 27% was measured from the uncovered furrows. Factors contributing to the differences in emissions were chiefly raised-bed configuration, tarp permeability, fumigant application method, soil properties, soil water content, and fumigant carbonation. The results indicate that strategies for emission reduction must consider the differences in agronomic production systems. Modifying raised bed configuration and fumigant application technique in coarse textured soils with TIF tarping can maximize fumigation efficiency and emission reduction.