| As common green manure in the south of China,milk vetch(Astragalus sinicus)and rapeseed(Brassica campestris)can improve soil quality and increase soil fertility after they are returned to the field.The long-term sapplication of chemical fertilizers is one of the important reasons for the degradation of the quality of cultivated soil in China,the combination of green manure return and chemical fertilizer is an effective measure to alleviate this problem.Soil aggregate stability is an important indicator of soil quality,and soil organic carbon is an important cement to keep aggregates stable.In this study,relying on the long-term positioning test station of rice-green manure rotation in Jingzhou,Hubei Province,the paddy soil of rice season and green manure season was used as the research object,and five treatments were selected: control(CK),single application of chemical fertilizer(F),return of milk vetch(MV),return of milk vetch to the field with chemical fertilizer(MVF),and rape return with chemical fertilizer(RPF).Using the method of combining wet sieving of aggregates and physical classification,to investigate the effects of long-term return of two kinds of green manure on soil aggregate stability and organic carbon sequestration under the application of chemical fertilizers.It provides the theoretical basis for returning green manure to paddy fields and fertilizing soil in southern paddy fields.The main results of this study are as follows:In this study,it was found that the combined application of chemical fertilizers with milk vetch and rape reduced soil p H and increased the contents of total nitrogen and alkalihydrolyzed nitrogen in the soil in the green manure seasons,with an increase of 6.83%-15.0% and 14.53%-29.44%,respectively;The content of available potassium increased by0.96%-10.63% after the application of chemical fertilizers to the field of rape: while the content of available potassium was reduced by 6.13%-7.39% after the return of chemical fertilizer to the field of milk vetch.This study-related analysis shows: the relative content of particle size >5mm and 2-0.25 mm had the most significant effect on the stability of aggregates;the return of Milk vetch under the combined application of chemical fertilizers increased the relative content of aggregates >0.25 mm in the soil in the two seasons,and increased the stability of the aggregates.The average weight diameter and the stability rate of large aggregates increased by 20.14%-21.88% and 7.23%-9.60%,respectively;although the relative content of aggregates > 0.25 mm in the soil of rapeseed was reduced(1.53%-1.72%)for two seasons after returning to the field,The stability rate of large aggregates was reduced(1.66%-1.70%),but the average weight diameter of the green manure season was increased by13.07%.The organic carbon content in the bulk soil and aggregates was increased under the combined application of chemical fertilizers with Milk vetch and rape.The increase range was 13.30%-22.22%;in the rice season,the organic carbon content of each particle-level aggregate after Milk vetch returning to the field with chemical fertilizers increased by13.06%-20.64%,which was higher than the increase of 4.85%-12.86% after the rapeseed was returned to the field,and in the green manure season,the increase of organic carbon content of particle size after rape returning to the field(9.0%-32.75%)was higher than the increase of organic carbon content after returning to the field of milk vetch(3.29%-19.57%).The highest organic carbon content in the aggregate density component is LFOC(111-459 g/kg),followed by CPOC(80.0-150 g/kg),FPOC(34.5-58.4 g/kg)and m SOC(7.5-12.5 g/kg)kg).The contents of LFOC and CPOC components in soil were both increased under the combined application of chemical fertilizers with Milk vetch and rape,and the two components increased by 1.15-2.14 times after Milk vetch returning to the field,and the two components increased by 1.03-1.87 times after rape returning to the field;while in m SOC,milk vetch returning to the field with chemical fertilizers has a larger increase of this component in the micro-aggregates,and the increase range is 1.15-1.27 times;the increase of this component in the macro-aggregates is higher after rape returning to the field.The increase range was 1.26-1.28 times,and both green manures promoted the accumulation of organic carbon pools.In the aggregates,it was found that the application of chemical fertilizers with Milk vetch increased the aggregate stability of >0.25 mm and the relative peak area of the organic functional group(aromatic C=C and aliphatic-CH),and the stability of the organic carbon of the large aggregate was correspondingly increased,and the increase was smaller with the smaller the particle size;and the two particle size of > 0.25 mm and <0.053 mm after the return of rape were as follows: the organic matter anti-decomposition index increased in the rice season,and the green mantle season decreased,which was significantly affected by the season.In the density components,after the return of milk vetch,the relative peak area of aromatic C=C and aliphatic-CH of CPOC increased,and the relative peak area of polysaccharide C-O decreased,and the m SOC change was reversed;while the seasonal influence of rapeseed was obviously affected by the season,and the relative peak area of aromatic C=C and aliphatic-CH in CPOC and m SOC decreased,the relative peak area of polysaccharide C-O increased during the rice season,and the green manure season was opposite.It shows that the return of Milk vetch to the field has a good effect on the stability of soil aggregates and the solidification of organic carbon in the two seasons compared with the return of rapeseed,and the return of Milk vetch is more suitable as an effective means to improve soil quality. |
