Impact Of Cultivating Green Manure Crops With Reduced Phosphate Fertilizer Application On Wheat Growth And Soil Properties Under Dryland Conditions Of The Loess Plateau

Phosphorus?P? is an essential element for all life forms on Earth.Phosphorus is the most important mineral nutrient after nitrogen?N?in crop production,which requires sufficient phosphorus supply in soil.However,overuse of phosphate fertilizer is common in China's grain production and other crop systems.Phosphorus mainly exists in inorganic form in calcareous soils in northern China,accounting for about 70-80%of total phosphorus in soils.After phosphorus fertilizer is applied to the soil,most of it is adsorbed and fixed by the soil,converted into slow acting state and accumulated in the soil with high steady-state,forming a huge potential pool of phosphorus,and how to reuse it is a difficult problem.The Loess Plateau is an important crop producing area in China,and winter wheat-summer fallow is one of the main cropping systems in this area.In the process of winter wheat planting,the excessive application of phosphorus fertilizer gradually increased.Cultivating green manure crops in summer fallow can increase soil fertility and improve rainfall utilization efficiency,which is one of the effective measures to develop sustainable agriculture.However,can cultivating green manures,affect soil chemical properties,activate soil insoluble phosphorus,increase soil available phosphorus content,promote winter wheat phosphorus absorption,reduce the amount of fertilizer phosphorus application?Such studies are rarely reported in under semiarid climatic conditions of Weibei dryland of the Loess plateau.A 3-years split plot experiment was conducted at the aims of evaluating the effects of different summer green manure crops and P fertilizer rates on the soil P availability,soil chemical properties including soil organic matter,residual NO₃-storage,total N content,also to figure out how these crops can reduce the high application of P fertilizer for subsequent crops and can affect the wheat growth in the Weibei dryland of the Loess plateau.The main plots consisted of three GM crops?black bean,rapeseed,and summer fallow as control?and 5 sub-treatments(synthetic P rates of 0,40,80,120,and 160 kg P₂O₅ha^-1 applied at wheat sowing).Three treatments(black bean,rapeseed at 80 kg P₂O₅ha^-1and fallow at 120 kg P₂O₅ha^-1)were also chosen in this study to refine the results.The main research results were listed below:1)The wheat yield,biomass,yield components?1000 kernel weight,number of spikes,harvest index?,P uptake,Partial factor productivity?PFP?in the GM treatments refining the data for three treatments with 80 kg P₂O₅ ha^-1 rate were similar with those in the fallow treatment with 120 P₂O₅ ha^-1 rate during the test 3 years.Green manures were not able to increase the wheat N and K content as compared to fallow.GM biomass&P accumulation were higher in black bean as compared to rapeseed.For two years 2018-2019,rapeseed and black bean increased the soil organic matter content by 5.7%,4.9%and 6.3%,5.6%in upper 0-10 cm depth as compared to the fallow.Similarly,for total nitrogen content rapeseed and black bean increased the content by 10.9%,4 and 6.1%,5%in upper 0-10 cm depth.Results showed that residual soil nitrate storage upto 200 cm depth in black bean increased by 12%,as compared the fallow.In general,growth of GM crops has great potential to increase the soil P availability and reduce the high-level P fertilization.2)Decomposition characteristics and accumulative nutrients?C,N,P?released rates of different green manures with above ground&below ground parts contained in nylon bags was measured in field experiments.Results showed that accumulative nutrient released rates for shoots were higher as compared to the roots,while rapeseed increased the both parameters as compared to the black bean.Rapeseed shoots and roots decomposed faster as compared to the black bean.During the first 30 days after incorporation in the soil,C released by green manures declined faster than N and P.The C:N&C:P ratio for both rapeseed shoot and root remained lower as compared to black bean.3)Rapeseed and black bean increased soil available P content by 31%as compared to fallow at lower P₀ level,while at higher P₁₂₀ level rapeseed only increased soil available P content by 4.8%.At P₀ and P₁₂₀ levels both,green manures?black bean&rapeseed?increased the labile Na HCO₃ Pi and moderately labile Na OH Pi content,significantly higher as compared to fallow.At P₀ level,Rapeseed and black bean increased Na HCO₃-Pi by 41%and 21%.At P₁₂₀level rapeseed increased Na HCO₃-Pi by 18%.Non labile fractions were not significantly different between green manures treatments.4)The ³¹P NMR spectra of the Na OH–EDTA-extracts of the fertilizers contained signal in all four diagnostic chemical shift regions?orthophosphate,orthophosphate monoesters,orthophosphate diesters and phosphonate?.Although,orthophosphate,orthophosphate monoester and diesters concentrations were not significantly different between green manures at both P₀&P₁₂₀ levels,but higher concentrations were found in green manures as compared to the fallowIn conclusion,growing GM crops instead of fallowing in summer could be a better strategy to maintains the P level and build a more sustainable winter wheat cropping system in the dryland region of China.