Effects Of Multiple Cropping Patterns On Soil Aggregates And Soil Organic Carbon In Paddy Fields

Multiple cropping system is an important way to improve soil multiple cropping rate,resource utilization rate and ensure food security.Based on double cropping rice in south China,this study uses the superior winter climate resources to plant different winter crops:Radish（rice-rice-radish）,Ryegrass（rice-rice-ryegress）,Potato（rice-rice-potato）,Rape（rice-rice-rape）and Milk vetch（rice-rice-milk vetch）were used as the control in field experiments.By monitoring the changes of soil aggregate,soil organic carbon and its components under different cropping patterns,the effects of different cropping patterns on the structure and stability of soil aggregate and the distribution and accumulation of soil organic carbon were discussed,so as to provide theoretical basis for the sustainable development of multi-cropping cropping patterns in paddy fields in south China.The main results are as follows:1.Winter cropping could improve soil physical structure,decrease soil bulk density and improve soil moisture retention and aeration,and Ryegrass treatment had the best effect.Compared with early rice and late rice,the soil bulk density in winter cropping season was the lowest,6.43%lower than that in early rice and 7.63%lower than that in late rice on average.The bulk density of Ryegrass in 0-20 cm soil layer was the lowest,and decreased by3.04%to 13.1%compared with the control.The total soil porosity and capillary porosity increased by 4.97%-6.04%and 35.82%-42.23%in winter cropping season compared with those in early and late rice seasons.In the late rice season,the bulk density of Potato treatment was the lowest and the total soil porosity was the highest in the 10-20 cm soil layer,and the capillary porosity of Ryegrass treatment was significantly higher than that of other treatments in different soil layers（P<0.05）.Compared with CK,the multiple cropping pattern in winter fallow was beneficial to improve soil porosity and soil structure,and the overall effect of each treatment was Ryegrass>Potato>Rape>Milk vetch>CK.2.The multiple cropping pattern can promote the composition of soil aggregates,improve the stability of aggregates,and increase the content of organic carbon in aggregates.The distribution of soil aggregates was as follows:large aggregates（LMa:>2 mm）>small aggregates（SMa:0.25-2 mm）>silt and clay components（S+C:<0.053 mm）>micro aggregates（Mi:0.053-0.25 mm）.The content of LMa in 5-20 cm soil layer was significantly increased in winter cropping season Ryegrass（P<0.05）,with an increase rate of2.19%-37.52%.LMa content in Potato treatment was the highest in early rice season.LMa content in Rape treatment was the highest in late rice season,which increased by 0.49%to11.79%compared with CK.Compared with CK,the aggregate stability in 5-10 cm soil layer in winter fallow crop compound pattern was significantly improved.In the soil layer of10～20 cm,the stability of aggregates was the best under Ryegrass treatment.Potato and Ryegrass treatments had the highest organic carbon content in aggregates.In the late rice season,the MWD,GMD and R_0.25values of aggregates at different depths were the lowest under Radish treatment,the stability of Rape aggregates was the strongest in 0-5 cm soil layer,and the stability of Ryegrass aggregates was the strongest in 5-20 cm soil layer.The value of R_0.25in all treatments was above 70%,and except for the Radish treatment,the other treatments showed an improvement compared with CK.The pattern of returning straw to field for winter fallow crops increased soil aggregate content to some extent and promoted the stability of soil aggregate.3.In winter cropping mode,SOC and LOC contents were significantly increased,and Ryegrass and Potato treatments had the best effect.With the deepening of soil depth,SOC content showed a downward trend,and was the highest in late rice season,which increased by 6.62%and 2.33%,respectively,compared with winter and early rice seasons.Ryegrass treatment was the highest,and increased by 9.58%,4.46%and 5.98%,respectively,in 0-5,5-10 and 10-20 cm soil layers compared with the control.The variation of soil active organic carbon（LOC）and microbial biomass carbon（MBC）was consistent with that of organic carbon.The LOC content of Potato was the highest,followed by Ryegrass.With the increase of planting time,the winter cropping season and early and late cropping season increased by5.03%-29.96%,8.02%-24.92%and 4.59%-23.93%,respectively,compared with the control.Soil MBC content in 0-10 cm soil layer was higher than that in 10-20 cm soil layer,and all treatments reached the peak at maturity stage,and Ryegrass treatment increased 53.67%（0-10 cm）and 53.98%（10-20 cm）in early rice season compared with control,respectively.The MBC content in late rice season was as follows:Ryegrass>Potato>Rape>Milk vetch>CK>Radish.4.Winter cropping pattern can increase effective panicle per plant,seed setting rate,1000-grain weight and double cropping rice yield to a certain extent.The actual yield of early rice was the highest in Radish treatment,which was 13.06%higher than CK;the actual yield of late rice was the highest in Milk vetch treatment,which was 11.29%higher than CK（P<0.05）,followed by Ryegrass treatment,which was 2.47%higher than CK.The effective panicle per plant in each treatment in early rice season was significantly higher than that in the control（P<0.05）,and increased by 8.06%～13.97%compared with the control.In late rice season,Milk vetch treatment had the most effective panicles per plant,which increased by11.4%compared with the control,and Potato seed setting rate was significantly higher than that of the control（P<0.05）.The 1000-grain weight in Milk vetch treatment was the highest.The annual yield of Radish treatment was lower than that of the control,and the yield of Milk vetch treatment was the highest,which increased by 10.73%compared with that of the control.