Study On Soil Water-fertilizer Effect And Microbial Diversity With Diffetent Winter Wheat-summer Green Manure Model In Dryland Of Loess Plateau

As a typical rain-fed agricultural region in China,the poor soil and long-term excessive inputof chemical fertilizers have led to the continuous decline of soil quality in The Loess Plateau,which has a certain impact on local food security and sustainable agricultural development.Planting and ploughing green manure in the summer fallow period of winter wheat can not only make fulluse of water and heat resources,but also effectively fertilize soil fertility,which is of great significance for reducing fertilizer application.The field experiment was conducted to investigate the effects of water and fertilizer and the effect on soil bacterial community structure by planting buckwheat(Fagopyrum esculentum Moench.),vetch(Vicia sativa L.),soybean {Glycine max(Linn.)Merr.},chickpea(Cicer arietinum Linn.),hairy vetch(Vicia villosa Roth.),alfalfa(Medicago sativa L.),prairie milk vetch(Astragalus adsurgens Pall.),black soybean {Glycine max(L.)merr.},mung bean { Vigna radiata(Linn.)Wilczek},catjang bean { Vigna cylindrica(L.)Skeels},sunn hemp(Crotalaria juncea L.),sweet clover {Melilotus officinalis(L.)Pall.},hyacinth bean {Lablab purpureus(Linn.)Sweet},wild soybean {Glycine max(L.)Merr.} and white clover(Trifolium repens L.)as green manure crops in the summer fallow period.Green manure crops suitable for winter wheat-summer green manure model in Dryland of South Shanxi Province were selected primarily.The results of this study will be used to fertilize soil and promote sustainable agricultural development for the region.The main results were as follows:(1)The research indicated that the biomass of green manure crops had a very significant positive correlation with water consumption,and the less the precipitation,the stronger the correlation by two years of field experiments.Experiments in 2018 showed that,under extreme drought conditions,excessive soil water consumption seriously affected the growth and development of winter wheat.Buckwheat had strong drought resistance,and the water storage capacity in the 2m soil layer is 55.7%(P <0.05)lower than that of the farmer pattern,and the leisure efficiency is only 24.4%,which led to a 67.0% reduction in wheat yield.The water storage capacity in the 2m soil layer of vetch,soybean and hairy vetch was reduced by 1.6% to8.7% compared with the farmer pattern.The difference was not significant,but wheat yield increased by3.9% to 19.7%.Experiments in 2019 showed that planting black soybean,mung bean,catjang bean,sunn hemp,sweet clover and soybean in the summer fallow period achieved higher biomass with a 26% to 35%reduction in water storage,and the biomass of unit water consumption was 5.20 9.68 kg/hm²/mm,significantly higher than other treatments.At the same time,the amount of N,P₂O₅ and K₂ O that could be replaced after ploughing is 27.0% 61.8%,8.8% 24.4% and 41.2% 110.6%.Therefore,from the perspective of water consumption and nutrient return,black soybean,mung bean,catjang bean,sunn hemp,sweet clover and soybean were primarily selected as green manure crops planting in the summer fallow period in Dryland of South Shanxi Province.(2)Studies on the response characteristics of the soil organic carbon and nitrogen components after the6 kinds of green manures that were screened as shown above showed that planting and ploughing green manures in the summer fallow period increased and activated the soil carbon and nitrogen pool.Among them,mung bean,soybean and black soybean treatments increased the content of soil active carbon and nitrogen components to a greater extent than other treatments.The contents of microbial biomass carbon(MBC),soluble organic carbon(DOC),particulate organic carbon(POC),and light fraction organic carbon(LFOC)increased by 41.2%,15.9%,11.1% and 96.7%,respectively,compared with the farmer pattern.And the contents of microbial biomass nitrogen(MBN),soluble organic nitrogen(DON),particulate organic nitrogen(PON),and light fraction organic nitrogen(LFON)increased by 28.2%?32.6%?15.4% and 38.6%,respectively,compared with the farmer pattern.The soil carbon and nitrogen components of other green manure trements were generally not significantly different from the farmer pattern or showed a certain downward trend.(3)The soil microbial community in wheat field of South Shanxi Province Dryland was mainly composed of Acidobacteria,Actinobacteria and Proteobacteria.Planting and ploughing green manures improved soil bacterial species diversity.The number of OTUs with green manure trements was 2.3% 8.8%higher than that of the farmer pattern.The Chao1,Observed species,PD whole tree,and Shannon indices in the alpha diversity index increased by 0.1% to 6.2%,1.3% to 8.7%,2.5% to 8.3%,and 0.5% to 2.2%,respectively,compared to the farmer pattern.Green manure treatments generally increased the relative abundance of soil proteobacteria,with an average increase of 24.9%;the relative abundances of soil acidobacteria and actinobacteria decreased by 14.1% and 14.0%.The composition of bacterial communities with mung bean and cypress,soybean and ramie treatments was similar,but the composition of bacterial community with black bean treatments was significantly different from other green manure treatments.Studies at the bacterial class level found that Subgroup 6,Alphaproteobacteria and Betaproteobacteria were the main bacteria affecting soil organic carbon content.In summary,on the basis of the winter wheat-summer fallow planting model on the Loess Plateau,the conversion to planting and ploughing green manures in the summer fallow period replaced the fertilizers N,P₂O₅,and K₂ O at 2.4% 61.8%,1.3% 24.4%,6.4 % 110.6%.At the same time,green manure treatments increased the diversity of bacterial communities,activated soil carbon and nitrogen components,and improved soil nutrient status.However,there was also a risk of excessive depletion of the soil water storage,which would affect the growth and development of wheat after extreme drought conditions.Comprehensively evaluate the water and fertilizer effects and microbial community characteristics of green manure cultivation,planting mung bean,soybean and black soybean as green manure crops to construct a winter wheat-summer green manure planting model in Dryland of South Shanxi Province,which is of great significance to the improvement of soil quality and the sustainable development of agriculture in the dry-growing wheat field of the Loess Plateau.