The Control Effect Of Metham-sodium To Soil-borne Dieases And Its Effects On Soil Microbial Population And Enzyme Activities In Summer Squash

Summer Squash(Cucurbila pepo L.) is a high-value crop in China. But this crop suffers from attack by soil-born diseases due to long-term continuous cropping and intensive regimes, which affect the quality and yield of Summer Squash. At present, the best treatment for the management of soil-born diseases is pre-plant soil fumigation with methyl bromide(MeBr). However, China has been supposed to phase out MeBr completely by2015because of its adverse effects on stratospheric ozone. So, searching MeBr replacements is imperative. Now, chloropicrin(CP), metham-sodium(MS),1,3-dichloropropene(1,3-D) and dazomet(DZ) are promising among subtive chemicals. MS can inhibit pathogens well with its high efficiency and low toxicity, but there isn’t any report about its actual effects on soil-born diseases and soil microbe ecological effect.In this study, the efficacy of MS to control soil-born pathogens was conducted in laboratory. The control effects of soil-born diseases and safety to Summer Squash were detected in greenhouse pot experiments as well as field trials. At the same time, traditional physiological and biochemical methods were used to determine the effects of MS on microbes, soil respiration and soil enzyme activities. The study evaluated the ecological safety of MS, offering a theoretical basis to the use of MS on Summer Squash. The results were as follows:Laboratory studies found that activities of metham-sodium to four target pathogens were much higher than1,3-dichloropropene. EC50values of metham-sodium to S. sclerotiorum、E. carotovora、F. oxysporum and P. aphanidermatum were0.060mg/L、0.945mg/L、1.380mg/L、2.953mg/L; and EC50values of1,3-dichloropropene to four pathogens above were516.654mg/L、928.558mg/L、633.784mg/L、77.242mg/L. The highest relative toxicity ratios was8610.90. We also found metham-sodium0.228mg/L could inhibit S. sclerotiorum germination completely. This showed that MS was more effective to soil-born pathogens than1,3-D.Pot trials showed that MS was effective on controlling S. sclerotiorum、E. carotovora、F. oxysporum and P. aphanidermatum and reducing the disease index. Meanwhile, MS could enhance the growth of Summer Squash, and the enhancing level was proportional to the concentration of MS.1,3-D could also control soil-born diseases of Summer Squash, but its effects were not good enough.Field trials of E. carotovora revealed that metham-sodium applied to the field at150、90、75、60kg/ha could suppress E. carotovora, which controling effects were88.94%、87.58%、 83.76%、80.60%、64.80%, while maintaining high summer squash marketable yields, better than1,3-dichloropropene at the concentration of200kg/ha.Fusarium spp. and Phylophthora spp. were inhibited after the soil was treated with MS. The dosage of MS was higher, the effect was better. More than95%of pathogens were inhibited after treated with concentration of90.28mg/kg, and pathogens were suppressed completely at the concentration of180.56mg/kg until the end of the test.The study of MS on the population of the soil microbes was detected by the plate-dilution method. The results showed as follows:metham-sodium had similar effects on soil bacteria and actinomycetes, both were inhibition-stimulation-recovery, but the effect on bacteria was more visble than actinomycetes. The highest stimulation of bacteria was293.61%, however, the actinomyces was180.77%. While metham-sodium at each concentration inhibited soil fungi at the test; the inhibition of high concentration (180.56mg/kg) was100%, and the level of inhibition was proper to the concentration of metham-sodium.Effects of MS on soil respiration were also detected in this study. The results showed that soil respiration was inhibited after the soil was treated with MS. The highest inhibition was84.47%after treated with concentration of180.56mg/kg. From2nd day, inhibition was gradually replaced by stimulation and the time of stimulation was inverse proportional to the concentration of the treatment. With time went by, stimulation decreased and accorded with comparison at last. Harm coefficient showed MS had little harm to soil.Four representative soil enzymes showed different dynamic changes after treated with metham-sodium. The effects of metham-sodium on soil invertase were dosage-dependent. When soil was fumigated with low or medium concentrations of metham-sodium, the effects showed stimulation-inhibition-stimulation-recovery, while those treated with high concentrations of metham-sodium showed inhibition-stimulation-recovery, and the stimulation was up to213.62%. To all of the concentrations of metham-sodium, soil urease activity presented irreversible inhibition impact. The effects of metham-sodium on soil phosphatase were inhibition-stimulation-recovery. The activities of catalase in soil treated with metham-sodium were inhibited at first, and then stimulated. Metham-sodium had great effect on soil urease, but to soil invertase, phosphatase and catalase, the effects were temporary without potential harm to soil fertility and crop growing.