Effects Of Green Manure Cover On Soil And Water Conservation And Nitrogen And Phosphorus Loss Of Citrus Orchard On Purple Soil Slop Farmland

The role of green manure covering in the field of water and soil conservation,nutrient storage,soil improvement,and fertilization has been recognized worldwide.Purple soil is characterized by strong coarseness and weak water and fertilizer conservation ability,which is mainly distributed in hilly areas of Sichuan Basin,China.Few studies on the effect of green manure cover the loss of water,soil,and fertilizer in purple soil,especially on the orchard of sloping farmland in purple soil with strong interflow.Therefore,this study conducts a worldwide meta-analysis of 85peer-reviewed publications from Web of Science and China National Knowledge Infrastructure(CNKI)databases to quantify the effectiveness of ground cover in runoff reduction,soil loss and nutrient losses.On this basis,a field plot experiment was conducted in the citrus orchard on sloping farmland of purple soil.And four treatments(Lolium perenne L.,Vicia villosa Roth var.,Orychophragmus violaceus and control(clean tillage))were set up to quantitatively monitored and studied the effect of green manure cover cultivation on water and soil conservation and the control effects on nitrogen and phosphorus loss under natural rainfall conditions(September 2018 to September 2020).The main results are as follows:(1)The meta-analysis showed that ground cover management significant ly reduced runoff,soil loss,and nitrogen(N)and phosphorus(P)losses in the runoff by48.5%,70.5%,53.4%,and 56.9%,respectively.The magnitude of the effect of ground cover management mainly depended on ground cover types,land slope,and climatic conditions.Cover cropping showed more efficiency in reducing runoff,soil,and nutrient losses than mulch management.Non-legume grasses were more effective than legumes,mainly attributed to the more excellent vegetation coverage of the perennial non-legume grasses than the annual legumes.The ground cover showed the most capacity to conserve water and soil at slopes between 10 and 15°,with the tendency to lose effectiveness when field slopes were greater than 15°.When pooling data according to different climatic conditions,the reduction of runoff,soil,and nutrient losses were highest when mean annual precipitation and temperature were above 800 mm and 20 °C,respectively.(2)The results of field experiments showed that green manure cover treatments reduced the annual surface runoff,interflow,and soil loss in the citrus orchard.The effects of green manure cover on surface runoff,interflow,and soil loss were different among different varieties.The trend of overall performance was Lolium perenne L.>Vicia villosa Roth var.> Orychophragmus violaceus.Compared with control(clean tillage),Lolium perenne L.treatment reduced the annual surface runoff by 23.20%,interflow by 18.50%,and soil loss by 58.34%,respectively.The interflow was the main runoff of purple soil slope farmland,accounting for 89.60%-90.60% of the total runoff;In the rainy season from June to July,the soil was over-saturated by rainfall,and the infiltration of green manure was promoted.The interflows by the treatments of green manure cover were higher than that of the control treatment(clean tillage)many times.(3)Under natural rainfall conditions,green manure cover cultivation in citrus orchards on purple soil slope farmland can effectively reduce the loss of various for ms of N and P in surface runoff and interflow.Compared with the control(clean tillage),green manure cover significantly reduced total N loss by 14.04%-42.53% and total P loss by 24.06%-49.23%.However,N and P loss in the runoff by different green manure covers were ranged from green manure varieties.The trend of overall performance was Lolium perenne L.> Orychophragmus violaceus > Vicia villosa Roth var.In addition,green manure treatments significantly reduced the fertilizer loss rate.Compared with the control(clean tillage),Lolium perenne L.,Orychophragmus violaceus,and Vicia villosa Roth var.reduced the N fertilizer loss rate by 42.74%,14.10%,and 19.60%,the P fertilizer loss rate by 44.90%,43.25%,and 55.44%,respectively.In conclusion,ground cover management in orchards can significantly reduce runoff,soil loss,and N and P loss of sloping farmland.The effect was related to orchard management,grass types,coverage,and conditions of the orchard.Green manure cover cultivation(Lolium perenne L.,Vicia villosa Roth var.,Orychophragmus violaceus)can effectively reduce the soil loss and N and P loss of citrus orchards on purple soil sloping farmland.Among them,Lolium perenne L.was the best.The results provide a theoretical basis for orchard managers to make decisions on preventing soil and water loss.Our results can also provide references for soil and water conservation,non-point source pollution prevention,and control of citrus orchards on purple soil slope farmland.