Effects Of Rice Straw Return On Soil Organic Carbon Fractions,phosphorus Fractions And Microbial Community In Cold Region

Northeast China is the largest cold japonica rice planting area,and black soil is widely distributed here.A great culturing of rice produced plenty of rice straw,causing serious environmental problems.Straw return is an important measure to achieve the sustainable development of rice.Soil organic carbon affects the soil nutrient supply,physical properties and microbial activity.Long-term agricultural production decreases the soil organic carbon content,and affecting the soil function.Phosphorus(P)is one of the essential nutrients for crop growth.When P is leached or absorbed by plants,there is no complement of P from external sources.The supply level of soil P affects the crop yield.Crop straw is rich in organic matter,nitrogen,P,potassium and other microelements.Straw return increases the source of soil organic carbon and P,changes the soil microbial community composition and enzyme activity.Straw return also has an effect on soil organic carbon sequestration and P supply,and finally affects rice growth.This experiment was conducted in the experimental and practical base of Northeast Agricultural University from 2016 to 2019.Long-term(?10 years)plot located experiment and pot experiment,short-term(3-4 years)pot experiment were used to study the effect of rice straw return amount,land use,rice straw return and a combination of P fertilizer,and different organic matter return on soil organic carbon fractions,P fractions,phosphatase activity,soil microbial community,P accumulation and yield of rice.The combination of long-term(?10 years)experiments and short-term(3-4 years)experiments were used to study the effect of rice straw return time on these indexes.The results showed that:(1)The rice straw return and abandoned farmland treatments increased the soil total organic carbon(TOC)and active organic carbon fractions content,and the increasing amount of active organic carbon fractions were higher than the TOC.Long-term(?10 years)rice straw return and abandoned farmland treatments significantly increased soil TOC,labile organic carbon(LOC),particulate organic carbon(POC),dissolved organic carbon(DOC),and microbial biomass carbon(MBC).The DOC and MBC content in abandoned farmland soil were significantly higher than those in paddy soil.After straw return for 3-4 years,high amount of rice straw return,decomposed rice straw return,and dairy manure return treatments significantly increased soil TOC,POC,DOC and MBC content,burning rice straw treatment significantly decreased soil MBC content.Rice root return significantly increased soil MBC content,but had no effect on other soil organic carbon fractions.P fertilizer increased the POC and MBC content under rice straw return.There was a positive correlation between soil TOC content and active organic carbon fractions.The influence of rice straw return on soil organic carbon fractions changed with the increase of returning time.(2)Long term(?10 years)rice straw return increased soil available P content,and the available P content increased with the increasing of straw return amount.High amount of rice straw return significantly increased soil available P content.The available P content in abandoned farmland soil was significantly lower than that in paddy soil.Rice straw return significantly increased the content of Na HCO₃-Pi,Na HCO₃-Po,Na OH-Pi,Na OH-Po and total P.The content of Na HCO₃-Pi,Na HCO₃-Po and Na OH-Pi in abandoned farmland soil were significantly lower than those in paddy soil,but the HCl-P content in abandoned farmland soil was significantly higher than that in paddy soil.Long term(?10 years)rice straw return significantly increased the proportion of labile and moderately labile P in total P,and significantly decreased the proportion of non-labile P in total P.Compared with the paddy soil,the proportion of labile and moderately labile P in total P were significantly decreased in the abandoned farmland soil,and the proportion of non-labile P in total P were significantly increased.After straw return for 3-4 years,high amount of rice straw return,decomposed rice straw return,and dairy manure return treatments significantly increased the content of Na HCO3-Pi,Na HCO3-Po,Na OH-Pi,Na OH-Po,available P and total P,and significantly decreased the proportion of non-labile P in total P.High amount of rice straw return,burning rice straw and dairy manure return treatments significantly increased the proportion of labile P in total P.Compared with no P fertilizer application,P fertilizer application increased the content of P fractions and the proportion of labile P in total P,and decreased the proportion of non-labile P in total P.Rice straw return increased the content and availability of soil P.(3)Rice straw return increased the soil phosphatase activity,which increased with the increasing of rice straw return amount.Long-term(?10 years)high amount of rice straw return significantly increased the soil acid and neutral phosphatase activity.The soil phosphatase activity was significantly lower in abandoned farmland soil than that in paddy soil.After straw return for 3-4 years,high amount of rice straw return,decomposed rice straw return and dairy manure return treatments significantly increased the soil phosphatase activity.Compared with no P fertilizer application,no rice straw return with P fertilizer application reduced the soil acid and alkaline phosphatase activity,and increased the soil neutral phospha tase activity;rice straw return with P fertilizer application increased the soil acid phosphatase activity,and induced the soil alkaline phosphatase activity.Soil phosphatase activity was affected by organic matter return,returning time,straw return amount and P fertilizer application.(4)Straw return enhanced the relative abundances of microbes involved in the carbon and P cycle.The dominant phyla included Proteobacteria,Bacteroidetes,Chloro flexi,Firmicutes,and Acidobacteria.The relative abundance of Proteobacteria was the highest,and the relative abundance of Verrucomicrobia was relatively stable in all treatments.Straw return enhanced soil microbial richness but did not influence soil microbial diversity.(5)The content of soil MBC,DOC,POC,and Na HCO₃-Pi impacted the microbial community composition under long term(?10 years)rice straw return.The content of soil DOC,TOC,POC,and Residual-P impacted the microbial community composition under rice straw return for 3-4 years.The soil P fractions had greater impact on microbial community than soil organic carbon fractions.(6)With the increase of returning time,the negative effect of straw return on rice yield became smaller.Long term(?10 years)rice straw return increased the rice yield,dry matter weight,and grain P accumulation.Rice straw return for 3-4 years reduced rice yield and plant P accumulation.The plant and grain P accumulation of rice were reduced under no P fertilizer application.Dairy manure return treatment increased rice yield and P accumulation of rice leaf,stem,and grain,and burning rice straw treatments significantly reduced grain P accumulation.