Effect Of Straw Returning On Soil Nutrient And Organic Carbon Components In Ratoon Rice Field

The vigorous development of ratoon rice is of great practical significance to the high quality and yield of rice in southern China and the national food security.However,the longer growth period of ratoon rice,fertilizer source of the bud-promoting fertilizer applied to the main rice and other seasons,can cause the lack of fertilizer in the middle and late stages of the ratoon rice,leading to the imbalance of soil nutrients.Improving ratoon rice soil fertility is an important measure to maintain its nutrient balance.Straw return is an important way to improve soil fertility and straw resource utilization.Under the ratoon rice cultivation system,little is known about the changes of soil nutrients and organic carbon components after straw returned to the field.In this study,field experiment was designed four treatments included no rice straw returning(CK),straw return of 7500 kg/hm~2(SH),straw return of 15000kg/hm~2(SW)and organic matter-decomposing inoculant application plus straw of return15000kg/hm~2(SWF);laboratory simulation experiment was designed four treatments included straw is not added(CK),the amount of straw added is 1%(RS1),the amount of straw added is 2%(RS2)and the amount of straw added is 2%plus organic matter-decomposing inoculant application(RS2F).The two experiments were carried out and determined changes in soil available nutrients and organic matter components to investigate the effect of different patterns of straw returning on ratoon rice soil physical and chemical properties and soil fertility.The main results are listed as follows:(1)After two years of the field experiment,compared with the control,straw returning treatments slightly increased soil pH.Treatments(SH,SW)increased soil alkaline nitrogen,available phosphorus and available potassium by 0.31%-4.25%,6.94%-17.35%and 10.66%-17.13%,respectively.compared with other treatments,incorporating rice straw return of 15000kg/hm~2 with organic matter-decomposing inoculant treatment has the best improvement effect,which increased by 5.86%,22.56%and 22.84%.Short-term laboratory simulation experiment found that straw addition treatments(RS1,RS2,RS2F)reduced slightly soil pH after 180 days of cultivation.Besides,straw addition treatments(RS1,RS2,RS2F)could increase soil nutrients in different degrees,and the increase range of different treatments was RS2F>RS2>RS1.Obviously,the increase in soil available nutrient of adding 2%straw with organic matter-decomposing inoculant is higher than other treatments.(2)Straw returning could improve the content of soil organic carbon and its components in ratoon rice fields,and the effect varied with the different straw returning patterns.SWF treatment is beneficial to increase the contents of soil organic carbon components,including dissolved organic carbon,particulate organic carbon and humilic acid carbon.Laboratory simulation experiment showed that straw addition treatments(RS1,RS2,RS2F)could increase the content of organic carbon and its components in varying degrees after 180 days of cultivation.The overall performance was RS2F>RS2>RS1.The content of soil organic carbon and humilic acid carbon significantly increased in the treatments RS2 and RS2F as compared to control,Compared with control,the contents of soil organic carbon increased by0.63%and 1.70%in the treatments RS2 and RS2F,respectively;while the contents of humic acid carbon increased by 11.50%and 15.00%,respectively.However,there was no significant difference between RS2 and RS2F treatments.The content of soil dissolved organic carbon RS2F treatment significantly increased,and the increment was 25.93 mg/kg.(3)Three-dimensional fluorescence spectrum maps showed that,the relative fluorescence intensity values of the dissolved organic matter was increased in the straw returning treatments,and the molecular structure of soil dissolved organic matter tends to be simple,compared with the treatment of no straw returning to the field.The relative fluorescence intensity values of dissolved organic matter in the ratoon rice harvest were significantly higher than that in the main rice harvest,it indicates that the soil dissolved organic matter structure tended to be simple during the growth period of ratooning rice,which might be accompanied by the decomposition process of organic matter.The results showed that straw returning could improve ratoon rice soil fertility.Different straw returning patterns could increase soil nutrient contents and organic carbon components contents by varying degrees.The combination of high straw returning amount and organic matter-decomposing inoculant application had a more significant effect.The results provide a theoretical basis for the fertilization and straw resource utilization of ratoon rice soil.