Effects Of Crop Rotation And Straw Returning On Paddy Soil Aggregates And Carbon Sequestration Characteristics

Rice-rape rotation and rice-wheat rotation are the main planting modes of paddy soil in Sichuan.The burning of straw causes serious environmental pollution.Returning straw to the field is an important way to realize resource utilization and sustainable soil utilization.However,the effect of returning straw to the field on soil aggregate organic carbon fixation and mineralization in different rotation patterns is still unclear.In this paper,relying on a field-oriented experimental base with a history of 14 years of crop rotation,this paper studies the change characteristics of soil organic carbon and aggregate organic carbon under different crop rotations and straw returning to the field;through indoor constant temperature cultivation,the mineralization characteristics of various particle size aggregates are studied.Combined with changes in carbon input,it reveals the differences in soil carbon sequestration rates and efficiencies under different crop rotation patterns and straw returning to the field.The main conclusions of this study are as follows:(1)Difference of soil carbon input under crop rotation and straw returnAfter 14 years of crop rotation and straw return treatment,there was no significant difference in the average annual carbon input and cumulative carbon input of the rice-rape and rice-wheat rotation,but the return of straw to the field caused the average annual carbon input and the cumulative carbon input of the different rotation models.The cumulative carbon input increased significantly(P<0.05).The soil carbon input of different crops under the two rotation modes is as follows:rice>wheat>rape,and the soil carbon input of different organs of each crop is as follows:straw>root and its exudates>stubble.(2)Dynamic changes of soil organic carbon under crop rotation and straw returnThe soil organic carbon content of the plow layer(0-15 cm)under the two rotation modes increased with the increase of the years of straw returning to the field,and the rice-rape rotation mode increased the organic carbon content of the plow layer more significantly.Under the two rotation modes,straw returning to the field has a significant effect on the change of soil organic carbon content in the 0-5 cm soil layer,but has no significant effect on other soil layers.This is related to the no-tillage mulching method adopted in this experiment.Correlation analysis shows that organic carbon content is negatively correlated with crop yield,indicating that total soil organic carbon content is no longer the main factor affecting crop yield.(3)The effect of crop rotation and straw return on soil aggregatesThe stability of soil aggregates showed that rice-rape rotation was better than rice-wheat rotation.In the rice-rape and rice-wheat rotation modes,the organic carbon content of soil aggregates is as follows:the medium aggregates(0.25-2 mm)is the highest,and the small aggregates(<0.053 mm)is the lowest.Straw returning to the field resulted in a significant increase in the organic carbon content of the medium aggregates in rice-rape rotation.The difference in the organic carbon storage of soil aggregates in rice-rape and rice-wheat rotations mainly lies in large aggregates(>2 mm)and micro aggregates(<0.053 mm),while the impact of straw returning on the organic carbon storage of aggregates of each grain size not obvious.After 60 days of indoor constant temperature cultivation,the two rice-rape and rice-wheat rotation modes and the total cumulative mineralization of aggregates of each grain size in the soil under the treatment of straw return are as follows:>2 mm is the highest,0.25～2 mm and<0.053 mm is the second,followed by 0.053～0.25 mm;the return of straw to the field improved the soil aggregates(0.25～2 mm),small aggregates(0.053～0.25 mm),and microaggregates(<0.053 mm).The total cumulative mineralization of organic carbon.The changes of soil aggregate mineralization amount and mineralization rate with incubation time accord with first-order kinetic equation and logarithmic function respectively.(4)The effect of crop rotation and straw return on the rate and efficiency of soil carbon sequestrationThe soil carbon sequestration rate of rice-rape rotation and rice-wheat rotation with straw returning to the field reached 1.59 and 1.35 t/(hm~2·a).The soil carbon sequestration efficiency of rice-rape rotation and rice-wheat rotation with straw returning to the field reached 17.36%and 13.45%.Returning straw to the field promotes the improvement of soil carbon sequestration rate and soil carbon sequestration efficiency.Soil carbon sequestration has not yet reached the"saturation"level.