Effects Of Different Farming Systems On Biomass,Decomposition Release Of Ryegrass And Soil Fertility

Numerous studies have shown that planting cover crops has a good positive effect on subsequent crops and the soil environment,but there are a few reports about the effects of previous and next crops on cover crop growth and decay.A 2-year（2020-2022）field experiments were conducted at the Agricultural Science and Technology Park of Jiangxi Agricultural University to investigate the effects of the main crop（sweet corn and soybean）and nitrogen application on cover crop（ryegrass）biomass,carbon and nitrogen accumulation and decay release.The trial was conducted in a completely randomised group design and included two cropping patterns（sweet corn monocropping-ryegrass（MC）,sweet corn|soybean intercropping-ryegrass（CS））and three nitrogen rates（0 kg/hm²（N0）,150 kg/hm²（N1）,300 kg/hm²（N2））.The experiment investigated:（1）the biomass,carbon and nitrogen accumulation and soil nutrients of ryegrass at harvest;（2）the changes of decomposition and carbon and nitrogen release of ryegrass after incorporation,and the dynamic changes of soil nutrients,enzyme activities and microbial community composition during the corresponding period.The main results obtained from the experiment are as follows:（1）In terms of biomass（fresh weight and dry matter biomass）of ryegrass in the 2years,compared to N0,both sweet corn monoculture and sweet corn intercropping significantly increased ryegrass biomss at N1 and N2 levels.At the N0 and N1 levels,the previous sweet corn intercropping reduced ryegrass biomass compared to monocropping;at the N2 level the previous sweet corn intercropping significantly increased ryegrass biomass compared to monocropping.Nitrogen application to the previous crop favoured a lower carbon to nitrogen ratio for ryegrass（mostly around 25）and increased nitrogen fertilization had a tendency to reduce the carbon to nitrogen ratio of ryegrass.In terms of soil nutrients,at the same level of N application,soil nitrate-N was significantly increased by 52.84%in the N2 level sweet corn intercropping pattern in 2021 compared to the monoculture,while soil ammonium-N significantly increased by 254.97%,in the N2 level sweet corn intercropping pattern in 2022.In 2021,compared to N0,whatever monocropping or intercropping,soil nitrate and ammonium nitrogen were significantly increased at N2 level.（2）The results of 2-year showed that the decomposition,carbon and nitrogen release of residues characteristics of ryegrass incorporation followed a fast and then slow trend.The effects of cropping system and nitrogen rate on ryegrass decomposition and carbon and nitrogen release were mainly concentrated in the period 0-28 days（early decomposition period）.In 2022,the decomposition rate and carbon release from residues of ryegrass after 56 days of turning under sweet corn intercropping at the same N0 level were significantly lower compared to monoculture,by 9.12%and 12.21%,respectively,indicating that the sweet corn intercropping pattern reduced ryegrass decomposition to some extent.In the 2021,compared to N0,ryegrass decomposition rate and carbon and nitrogen release under N2 were significantly increased by 3.57%,11.49%and 5.57%,respectively,at the 28^thday of ryegrass incorporation in the sweet corn intercropping system.（3）The results of 2-year showed that ryegrass incorporation had a tendency to increase soil organic matter and alkaline decomposition nitrogen,but a tendency to decrease soil p H.The retention time of soil nitrate-and ammonium-nitrogen in the soil was prolonged after ryegrass incorporation in 2022 compared to 2021.In terms of soil enzyme activity,soilβ-glucosidase activity was strongly influenced by cropping pattern and N application with a significant increase.Soil sucrase activity was significantly affected by N application at 2022.Soil sucrase activity showed an increasing trend in 2022 compared to2021;soil urease activity was significantly influenced by nitrogen application and its activity increased significantly with the increase in nitrogen application.（4）The results of the 2-year results showed that the cropping pattern and the nitrogen rate had a significant effect on the bacterial communities of Actinobacteria and Bacteroidetes.In 2021,compared to monocropping,there was a significant increase of90.00%in Actinobacteria in the sweet corn intercropping at N0.In 2022,there was a significant increase of 30.70%in Actinobacteria in sweet corn intercropping at N2compared to N0.Cropping system and nitrogen rate had a significant effect on Chytridiomycota and Olpidiomycota in the fungal microflora.Cropping pattern and N application did not significantly affect the Simpson and Shannon indices of soil bacterial and fungal communities.Compared to N0,the number of OTUs,ACE and Chao1 indices of soil bacterial communities were significantly decreased at the N1 and N2 in the monoculture pattern in 2022,which reduced by 11.29%,11.15%and 11.23%at N1,respectively,and reduced by 12.72%,12.84%and 12.71%at N2,respectively.