Study On Effects Of Planting Years And Pesticides On Microbial Number And Enzyme Activities In Vegetables Solar Greenhouse Soil

With the soil from open vegetable fields (control) and the vegetables solar greenhousesplanted for2,4,6,11,13,16,19years, respectively, as test materials, using the traditionalmeasurement method, the effects of planting years and commonly used pesticides(chlorothalonil, imidacloprid and metalaxyl mancozeb) on microbial flora and enzymeactivities were studied in this paper. Sustainable use of soil in greenhouse and safety evaluationof the use of pesticides provide a basis for the theoretical basis. The main results are as follows:1. Effects of planting years on microbial number and enzyme activities in vegetablessolar greenhouse soil(1)With continuous increasing planting years, soil organic matter and and availablenitrogen increased significancly, reaching maximum in the planting for11years, increasedby35.6%and60.9%respectively compared with the control and then decreased; total nitroge n,total phosphorus and total potassium increased steadily, reaching maximum in the planting for19years; available P and available K showed the same trend of organic matter’s, reachingmaximum in the planting for16years.(2)With continuous increasing planting years, soil bacteria, actinomycetes and totalmicrobial counts increased significancly, reaching maximum in the planting for11years,increased by54.8%,63.7%and55.4%respectively compared with the control and thendecreased; fungi increased steadily, is about2.2times in19years planted soil as that of thecontrol.(3)The numbers of microbial physiological groups of aerobic cellulose-decomposer,aerobic azotobacter, nitrite bacteria, denitrifier and sulphur reducer showed the same trend ofbacteria’s, which numbers in11years planted soil were1.5,1.6,1.9,1.4and1.1times comparedwith the control, respectively; the number of ammonifiers decreased firstly and then increased,and reached the minimum in13planting year, which was only56.0%compared with thecontrol.(4)The soil enzyme activities of Urease, Polyphenol oxidase, Sucrase, Protease, Cellulaseand Alkaline phosphatase increased and then deceased slightly with increase of planting years,but Catalase activity was stable.(5)Correlation analysis showed that soil organic matter, total nitrogen, total potassium andavailable nitrogen had positive correlation with the number of microorganisms, reachingsignificance at0.05or0.01levels; total phosphorus, available P and available K reachingsignificance at0.01levels with number of fungi. Urease, Polyphenol oxidase, Protease,Cellulase and Alkaline phosphatase had positive correlation with soil organic matter, reachingsignificance at0.01levels; Polyphenol oxidase had positive corre lation with total nitrogen,reaching significance at0.05levels; Urease, Sucrase and Catalase had negative correlation withtotal phosphorus, available P and available K, but less than significant level; Polyphenoloxidase, Protease and Cellulase had positive correlation with total potassium and availablenitrogen, reaching significance at0.01levels. Bacteria, actinomycetes and number of totalmicroorganisms had positive correlation with soil enzyme activities, reaching significance at0.05or0.01levels; fungi had negative correlation with activities of Urease, Sucrase, Catalaseand Alkaline phosphatase, and reaching significance at0.05levels with activities of Catalase.2. Effects of pesticides on microbial number and enzyme activities in vegetables solargreenhouse soil (1)The soil bacteria, fungi and actinomycetes in different planting years greenhousetreated with chlorothalonil were all produced different degrees of inhibition, the higher theconcentration of chlorothalonil was used，the more obvious inhibition rate we got, fungi wasthe most sensitive on chlorothalonil, bacteria and actinomycetes followed by fungi.The higher the concentration of chlorothalonil was used on soil urease activity，the moreobvious inhibition rate we got, at the same concentration, the inhibition rate increased and thendecreased with continuous increasing planting years; at medium a nd low concentrations, theinfluence of chlorothalonil on soil sucrase activity had a trend of stimulation, at highconcentrations, had a trend of inhibition; the influence of chlorothalonil on soil catalase activityhad a trend of initially stimulation and then inhibition; the higher the concentration ofchlorothalonil was used on soil alkaline phosphatase activity，the more obvious inhibition ratewe got.(2)With the concentration was increasing, the influence of imidacloprid on bacteria had atrend of initially inhibition after stimulation, and then inhibition; the influence of imidaclopridon fungi had a trend of initially stimulation and then inhibition; the higher the concentration ofimidacloprid was used on actinomycetes，the more obvious inhibition rate we got.At low concentrations, the influence of imidacloprid on soil urease and catalase activityhad a trend of stimulation, at medium and high concentrations, had a trend of inhibition; thehigher the concentration of imidacloprid was used on soil sucrase activity，the more obviousinhibition rate we got, at the same concentration, the inhibition rate increased and thendecreased with continuous increasing planting years; the higher the concentration ofimidacloprid was used on soil alkaline phosphatase activity，the more obvious inhibition ratewe got.(3)With the concentration was increasing, the influence of metalaxyl mancozeb onbacteria had a trend of initially stimulation and then inhibition; the higher the concentration ofmetalaxyl mancozeb was used on fungi，the more obvious inhibition rate we got; the influenceof metalaxyl mancozeb on actinomycetes had a trend of initially stimulation and theninhibition.The higher the concentration of metalaxyl mancozeb was used on soil urease activity，themore obvious inhibition rate we got; the influence of metalaxyl mancozeb on soil sucraseactivity had a trend of stimulation in the applied amount of pesticide is1.00mg/kg, and theinfluence had a trend of inhibition in the applied amount of pesticide is1.40-4.50mg/kg; withthe concentration was increasing, the influence of metalaxyl mancozeb on soil catalase activityhad a trend of initially inhibition after stimulation, and then inhibition; with the concentrationwas increasing, the influence of metalaxyl mancozeb on soil alkaline phosphatase activity hada trend of initially stimulation and then inhibition.In summary, in order to maintain the sustainable utilization of the vegetable greenhousesoil, improve soil fertility, reduce soil microbial pesticide resistance, should be proper controlof continuous planting years, preferably less than10years is appropriate, so that the soil canget enough buffer time to restore soil productivity. And application of pesticides should choosethe appropriate dosage, so that makes the economic, ecological and social benefits of thevegetable industry to improve in a comprehensive manner.