| Cover crops play a key role in improving soil,increasing soil nutrient content and reducing pests,insects and weeds,and are one of the core green technologies to achieve sustainable development goals of organic agriculture.In recent years,due to the increasing demand for "green living" among people,the single-seed and fertilization system of traditional plantations have been considerably impacted.Long-term single species with a large amount of fertilization will lead to excessive production costs of tea plantations,and will also cause deterioration of soil quality,biodiversity reduction and ecological function decline,which can no longer meet the requirements of production and development of green ecological tea plantations,and expose the urgent problems to be solved in the soil ecosystem of tea plantations.So far,few studies at home and abroad have evaluated the effects of cover crop planting and decomposition on soil nutrients in tea plantations,and the microbial regulatory mechanisms still need more research.Therefore,in this experiment,three planting areas(Longjing longleaf LJ.CY,Longjing 43 LJ.43 and white tea BC)were selected in nascent tea plantations with white clover as the cover crop.At the same time,three treatments:clear tillaging,intercropping white clover and laying weedproof cloth were selected to compare the soil properties and enzyme activities of tea plantations under different surface cover treatments.Then,the decomposition and nutrient release characteristics of white clover,as well as the response of soil properties,enzyme activities and bacterial communities to the decomposition of white clover were studied by nylon mesh bag method.The main results of this study are as follows:(1)Intercropping white clover and laying grass-proof cloth showed good water retention function and could effectively prevent soil acidification in tea plantations.However,both surface cover methods significantlyreduced the soil organic matter and ammonium nitrogen content(P<0.05).After intercropping white clover,the content of soil total phosphorus and available phosphorus increased significantly(P<0.05).Both surface cover methods tended to reduce the soil β-glucosidase activity in tea plantations,and the acid phosphatase activity was significantlyincreased under both treatments(P<0.05).In the three tea planting areas selected in this experiment,the comprehensive effect of intercropping white clover was better than that of laying grass cloth.(2)The decomposition of white clover in tea plantation soil can be divided into rapid decomposition period(0-14 days),slow decomposition period(14-34 days)and decomposition stagnation period(34-41 days),and the release of carbon and nitrogen is consistent with its decomposition law.The carbon-nitrogen ratio of white clover residues in LJ.CY,LJ.43 and BC soils showed a trend of first decreasing and then increasing and then stabilizing,and all reached the minimum value on the 9th day of decomposition.(3)Soil pH of tea plantation increased significantly in the early stage of white clover decomposition,and gradually decreased after 20 days and finally became neutral.The content of soil organic matter,ammonium nitrogen and nitrate nitrogen increased mainly in the early stage of decomposition(2-14 days),and then gradually decreased,but the content at 41 days of decomposition was still higher than that at 2 days of decomposition.Overall,during the decomposition of white clover,soil total nitrogen content increased significantly(P<0.05),but the content of total phosphorus and available phosphorus showed a downward trend.In addition,white clover decomposition had a significant positive effect on the activity of β-glucosidase involved in soil carbon cycling(P<0.05),but the opposite effect was on urease activity involved in nitrogen cycling.Soil acid phosphatase activity fluctuated around 20 μmol·d-1·g-1,and as the decomposition time increased,the acid phosphatase activity decreased to a value comparable to the activity on day 2 of decomposition.(4)White clover decay reduced the α-diversity of soil bacterial communities in tea plantations,but increased the relative abundance of soil dominant phylums,such as Actinobacteriota and Cyanobacteria.The carbon-nitrogen ratio of white clover residue is a key factor in regulating the abundance of Actinobacteriota and Cyanobacteria.With the decrease of the carbon-to-nitrogen ratio of white clover residue,the relative abundance of soil Actinobacteriota increased significantly(P<0.05),which promoted the decay of white clover and increased the content of organic matter and total nitrogen.Microorganisms belonging to Cyanobacteria also increased soil total nitrogen content through nitrogen fixation.β-glucosidase activity involved in soil carbon cycling fluctuated with the change of relative abundance of Actinobacteriota and Cyanobacteria,affecting the turnover of soil organic matter and other nutrient content.In addition,the study found that soil microorganisms belonging to Cyanobacteria had a phenomenon of "nitrogen fixation and phosphorus consumption",and it was suggested that when tea plantations used white clover as green manure,phosphorus fertilizer should be supplemented in time or or mixed planting a variety of green manure to maintain the balance of soil elements.In summary,grass mulching in nascent tea plantations can improve the ability of soil water storage and moisture-preservation,increase soil total nitrogen content,phosphorus content,and enzyme activities which related to nitrogen and phosphorus cycling.The use of white clover as green manure can also increase the content of organic matter,total nitrogen and other nutrients by increasing the relative abundance of key phylums in tea plantation soil.Therefore,white clover as a cover crop,combined with proper field management,is the ideal choice for constructing multi-species commensal compound cultivation mode in tea plantations,which is conducive to realizing sustainable development of tea plantation production. |
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