Effects Of Different Weeding Methods On Soil Physicochemical Properties And Microbial Diversity In Vegrtable Fields

Green agriculture is the theme of China’s agricultural development,while farmland weed pose a serious threat to the development of agricultural production in China.Weeding is the key to ensure the quality of agricultural production,and its environmental and ecological impact is worthy of attention.With the development of agricultural science and technology,weeding methods are constantly diversified.The existing studies focus on the effects of different weeding methods on soil physicochemical properties and herbicide residues,but their effects on microorganisms are largely unknown.In this study,agricultural film mulching,rice straw mulching and prodiamine(chemical herbicide)were selected as the weeding methods and we compared the effects of three different weeding methods on the physicochemical properties and enzyme activities in soils planted with Momordica charantia L..In addition,the differences and dynamic changes of soil microbial biota and community structure under different weeding methods were investigated by real-time PCR and high-throughput amplicon sequencing technology.On this basis,the degradation dynamics of different concentrations of prodiamine in non-sterilized soil and sterilized soil under indoor culture conditions were monitored and compared.The changes of soil microbial diversity and community composition under high concentration prodiamine treatment were measured by high-throughput sequencing technology.The main results are as follows:(1)Effects of different weeding methods on soil physical and chemical properties.Both agricultural film mulching and straw mulching resulted in a decrease in soil p H,while prodiamine significantly increased soil p H.Straw mulching had a positive effect on fertility conservation that total and available nitrogen,phosphorus,potassium,organic matter and soluble carbon increased.Soil total nitrogen,alkali-hydrolyzable nitrogen,available potassium,organic matter and soluble carbon in agricultural film mulching treatment decreased significantly,while total and available potassium and total phosphorus increased slightly.The alkali-hydrolyzed nitrogen,available phosphorus,total nitrogen,phosphorus,potassium and organic matter of prodiamine treatment were increased.(2)Effects of different weeding methods on soil enzyme activities.The activities of urease and sucrase were significantly decreased,while the activities of neutral phosphatase and alkaline phosphatase were significantly increased under all weeding treatments.In agricultural film mulching and straw mulching and prodiamine addition treatments,urease activity decreased by 22.23%,46.08% and 34.85%,sucrase activity decreased by 49.25%,31.87% and 33.40%,neutral phosphatase activity increased by19.25%,7.96% and 20.38%,and alkaline phosphatase activity increased by 147.09%,89.90% and 74.39%,respectively.Soil acid phosphatase activity decreased and catalase increased significantly by using prodiamine,while soil acid phosphatase activity increased and catalase decreased significantly under agricultural film mulching and straw mulching treatments.(3)Effects of different weeding methods on soil microorganisms.The results of soil bacterial and fungal quantification based on Real time PCR showed that the treatment of agricultural film mulching did not significantly affect the number of soil bacteria,and both rice straw mulching and prodiamine significantly increased the number of soil bacteria,and the effects of the three weeding methods on the number of bacteria were ranked from largest to smallest: prodiamine > rice straw mulching > agricultural film mulching.All three weeding methods significantly increased the number of fungi,and the effect on the number of fungi was ranked from largest to smallest: straw mulching >prodiamine > agricultural film mulching.Agricultural film mulching,rice straw mulching and prodiamine addition treatments all led to decrease in soil bacterial diversity and a significant increase in the number and diversity of soil fungi.Overall,the structure and function of soil bacteria were less affected by different weeding methods,while the composition and function of fungal communities changed significantly.There was a significant correlation between soil physicochemical properties and the relative abundance of some microbial genera.(4)The degradation dynamics of prodiamine and changes of soil microorganism under constant indoor light-proof incubation conditions.The half-lives of prodiamine in unsterilized soil were 76-110 d and in sterilized soil were 108-140 d.The degradability grade was classified as difficult.High-throughput amplicon sequencing results showed that high concentrations of prodiamine(75 mg/kg soil)had a significant inhibitory effect on beneficial bacteria such as Bacillus spp.,Sphingomonas spp.,and Azohydromonas spp.,compared with bacterial community structure,high concentrations of prodiamine had a greater effect on fungal community structure.The correlation analysis between the residual amount of prodiamine and the relative abundance of microorganisms at the genus level showed that the relative abundance of the genus Rhodococcus,the functional bacteria for bioremediation of environmental pollution,had a significant positive correlation with the residual amount of prodiamine,and increased substantially within a short period of time after the prodiamine treatment.It was speculated that high concentration of prodiamine residues in soil could change the microbial community structure in a short period of time,and long-term application of prodiamine might inhibit the growth of beneficial bacteria in soil,while the microflora with ecological remediation function played an important part in the degradation of prodiamine process.