| Straw return is the important carbon source for improving soil organic carbon(C)and nitrogen(N)in the field ecosystem,and straw burned is also a commonly phenomenon in South China.In order to explore the effects of long-term straw return mode on soil organic C and N in double-cropped rice in South China.With the aid of the straw return positioning study platform established in 2009,the effects of difference among straw directed return(SR),straw burned return(SBR)and fertilization with straw removal(F)on the yield and soil organic C and N fraction differences of double-cropped rice were studied under the condition of the same nitrogen,phosphorus and potassium nutrients input.The results indicated that:In 2017-2019,straw return and burned return increased early rice yield,three years on average by 7.21% and 7.67%,respectively.As to the yield composition,straw return increased grains per panicle in double-cropped rice,but reduced effective panicles in late rice.In addition,the dry matter accumulation of straw return has an advantage than fertilization with straw removal,especially in late growth period,which had increased by5% ～ 7% in early rice,and 2% ～ 6% in late rice.Compared to F,long-term straw return could increase total organic carbon(TOC)by3.9% ～ 7.4%.The soil microbial biomass carbon(MBC)in double-cropped rice and the light fraction organic carbon(LFOC)in late rice was increased by straw return.However,SBR did not improve SOC fractions with the decreased easily oxidizable organic carbon(EOC)in late rice though significantly increase dissolved organic carbon(DOC)contrast to CK.Compared to F,straw return improved soil total nitrogen(TN)in early rice,but reduced in late rice.Straw return and burned return increased hydrolysable unidentified N in late rice.However,compared to straw burned return,straw return also improved soil microbial biomass N(MBN)in double-cropped rice and the early rice of soil acid hydrolysis total N(HTN),ammonium N(AN)and amino acid N(AAN),which soil TN,AN and AAN were significantly correlated with early-and late-rice yieldStraw return increased soil C/N ratios in late rice.Soil microbial biomass entropy was also increased by straw return in early-and late-season.The ratio of soil MBC and MBN had no differ among three of application treatments.The results of principal component analysis showed that the soil organic C and N fractions of straw return had obvious advantages in early paddies,but its advantages had weakened in late rice.Overall,straw return has an advantage in early rice yield,dry matter accumulation and soil organic C and N fractions,but its advantages are diluted in late rice.However,the soil organic C and N fractions of straw burned return and fertilization with straw removal is almost accordant,and even some fractions are reduced,which indicates that straw return is more beneficial to the accumulation of soil organic C and N fractions than straw burned return,and the utilization of rice straw resources is more reasonable. |
