Effects Of Inter-row Grass And Tree Disk Mulching On Soil Physical And Chemical Properties And Microbial Communities Of Apple Orchards On The Weibei Dryland

Soil quality is one of the most important indicators for evaluating environmental quality,improving soil quality helps to promote the sustainable development of agriculture.Fruit industry,which has become an important characteristic and pillar industry in the Loess Plateau region in recent years,faces some challenges due to the traditional orchard soil management modes,such as clear tillage and excessive application of chemical fertilizers.These modes lead to poor soil structure,low soil health level,and affect the quality and yield of fruits,which restricts the sustainable and healthy development of fruit industry to some extent.Orchard grass cover,a green and safe orchard soil management mode,has gradually become an effective mode of modern orchard management.It has been widely recognized and applied for its effects on soil modification and fertilization,evaporation suppression,moisture conservation,and improving field microclimate.Thus,Experiments were carried out in 5-yearold apple orchards on the Weibei dryland,and four treatments were set up in the inter-row:sweetclover grass(Melilotus officinalis L.),perennial ryegrass(Lolium perenne L.),perennial ryegrass + alfalfa(Lolium perenne L.+ Medicago sativa L.)and clear tillage.Four grass mulching treatments were also set up in the tree disk: sweetclover mulching,perennial ryegrass mulching,perennial ryegrass + alfalfa mulching and no mulching.The physicochemical properties and enzyme activities of 0～20 cm and 20～40 cm soil layers under different inter-row treatments and 0～20cm soil layer under tree disk treatments were measured.16 S r DNA and ITS2 high-throughput sequencing techniques were used to measure the soil microbial diversity and community structure under different grass mulching measures.The mechanism of improving orchard soil quality under different inter-row grass and tree disk mulching measures was revealed.The main results are as follows:(1)Different grass treatments resulted in differences in soil bacterial and fungal diversity and community composition.Compared with clear tillage control,three grass mulching treatments increased the alpha diversity of bacteria and fungi,and the microbial diversity in the 0～20 cm soil layer was higher than that in the 20～40 cm soil layer.The dominant phyla of soil bacteria were Proteobacteria,Actinobacteria and Acidobacteria.All three grass treatments increased the relative abundance of Planctomycetes in the 0～20 cm soil layer.Sweetclover and perennial ryegrass + alfalfa increased the abundance of Proteobacteria and Bacteroidete.In the 20～40 cm soil layer,compared with the control,the three grass mulching treatments only increased the relative abundance of Proteobacteria.The dominant fungi in the soil was Ascomycota.In both 0～20 cm and 20～40 cm soil layers,sweetclover and perennial ryegrass+ alfalfa treatments increased the relative abundance of Ascomycota.(2)Compared with conventional tillage,the three grass mulching treatments(sweetclover,perennial ryegrass,and perennial ryegrass + alfalfa)significantly increased the soil organic matter,total nitrogen,nitrate nitrogen,ammonium nitrogen,and available potassium content in the 0～20 cm soil layer(P<0.05),but reduced the microbial nitrogen content.Compared with the control,the organic matter content increased by 43.8%,37.1%,and 34.7%(P<0.05),the total nitrogen content increased by 116.7%,87.5%,and 129.2%(P<0.05),the nitrate nitrogen content increased by 53.6%,29.5%,and 35.2%(P<0.05),the ammonium nitrogen content increased by 12.5%,20.8%,and 33.3%(P<0.05),and the available potassium content increased by 28.1%,21.1%,and 14.6%(P<0.05),while the microbial nitrogen content decreased by 22.8%,1.93%,and 40.5%,respectively.The soil nutrient content in the 0～20 cm soil layer was higher than that in the 20～40 cm soil layer,and the grass treatments had a more significant effect on nutrient enhancement.The soil mechanical stability aggregates in the0～20 cm and 20～40 cm soil layers were dominated by aggregates with a particle size >5 mm(23.25%～71.42%),while the water-stable aggregates were dominated by aggregates with a particle size <0.25 mm(38.02%～64.45%).All three grass treatments increased the mechanical stability aggregates with >5 mm,while the sweetclover treatment increased the water-stable aggregates with <0.25 mm.The activity of soil urease,sucrase,and alkaline phosphatase in the 0～20 cm soil layer was increased under the grass treatments and was higher than that in the 20～40 cm soil layer.Soil organic matter,total nitrogen,microbial carbon,and some bacteria had a positive correlation,which may be related to the bacterial community composition.(3)Sweetclover had high content of total nitrogen,while perennial ryegrass had higher organic carbon content and higher content of cellulose and hemicellulose than alfalfa.The three grass mulching,including sweetclover,perennial ryegrass,and a mixture of perennial ryegrass and alfalfa,could increase the content of ammonium nitrogen and microbial carbon in soil,but decreased the content of microbial nitrogen.All three grass mulching could reduce the bulk density of soil in the tree disk,with sweetclover having the most significant effect,and they all significantly increased the content of mechanical stability aggregates with a particle size of >5 mm(P<0.05),which were 28.9%,75.7%,and 63.8%,respectively.Compared with the control group,the three grass mulching increased the activity of soil urease and alkaline phosphatase,and increase the relative abundance of Proteobacteria and Bacteroidota in bacteria,as well as the abundance of Ascomycota in fungi.Furthermore,there is a positive correlation between soil total nitrogen,ammonium nitrogen,microbial carbon,and Ascomycota.