Research On Characteristics Of Carbon And Nitrogen Cycling Under Ecological Intensification Management In A Summer Maize-Winter Wheat Rotation System

The rotation system of summer maize-winter wheat in North China Plan is highly intensive.The rotation system characterizes by high nitrogen(N)fertilizer application rate,low fertilizer use efficiency,and heavy environmental pollution that damage its sustainability.It is urgent to optimize N management and develop ecological intensification management.Ecological Intensification management is a comprehensive management system which optimizes nutrient management and combines other advanced agronomy practices in intensive agricultural areas to achieve sustained yield growth while reducing environmental risks.In this study,we set up an Ecological Intensification(EI)management which is based on Nutrient Expert system and combined with improved varieties and optimized plant density.The characteristics of EI management were investigated on crop yield,N uptake,N use efficiency,soil carbon(C)and N sequestrations and N supply,C and N environmental effects through a 11-year field experiment by comparing with Farmers' Practices(FP).Moreover,we used DNDC model to simulate crop yields and reactive N losses and proposed an optimal management strategy for the winter wheat-summer maize rotation system.The main results are as follows:1.EI treatment reduced the N fertilizer application rate,simultaneously maintaining maize and wheat yields and improving N use efficiency.Compared with FP treatment,EI reduced the N fertilizer application rate by 22.4% without sacrificing grain yields,increased the apparent and cumulated recovery efficiencies of the N applied by 9.7 and 8.3 percentage points,respectively,and improved agronomic efficiency and partial productivity of the N applied by 32.3% and 30.1% percentage points,respectively,and increased the current and residual use efficiencies of the N applied by 6.6 and 2.7,respectively,and reduced the ratio of apparent N loss and the rate of apparent N loss by 9.3 percentage points and 87 kg/ha/year,respectively.2.EI treatment significantly increased the soil C sequestration rate and efficiency.Organic matter contents in 0-20 cm soil profile after maize harvest in 2018 were significantly increased compared to that in 2009.The soil organic C storage of EI treatment in 2018 was significantly higher than FP treatment.The soil C sequestration rate and efficiency of EI treatment(1.04 t/ha/year and 18.6%,respectively)were significantly higher than that of FP treatment(0.68 t/ha/year and 0.4%,respectively).No significant difference of soil N storages of 0-20 cm soil profile in 2018 was observed between EI and FP treatments.The mineralization potential of the two treatments increased with increasing incubation temperature,but no significant difference was observed between EI and FP treatments.3.EI treatment optimized N supply of winter wheat and summer maize,and reduced environmental risk.An indicator of the total N supply(TNsupply)was established by integrating multiple sources of available N.The suitable TNsupply was estimated to be 330-482 kg/ha for wheat and291-361 kg/ha for maize,respectively,through quantifying the response relationships between TNsupply,relative yield,N input,and N output.The N supply level of EI was closed to the suitable TNsupply,while the TNsupply of FP was 21.7%-30.2% higher than that of EI,which posed a higher environmental risk.4.EI treatment reduced C and N footprints of summer maize and winter wheat production.Compared with FP treatment,EI reduced soil nitrous oxide emissions by 1.5% and 13.4%,reduced ammonia volatilization by 14.9% and 19.3%,reduced N footprints by 20.5% and 27.2%,reduced C footprints by 9.7% and 22.1%,for wheat and maize,respectively,and increased annual net income by14.5%.Thus,EI management is a sustainable management approach that balances environmental and economic effects.5.DNDC model performed well in simulating wheat and maize yield,N uptake,and reactive N loss.Further optimal agronomic practices were summarized.The DNDC model performed well in simulating crop yield,N uptake,nitrous oxide emission and ammonia volatilization in the winter wheatsummer maize rotation system.Based on the results of the sensitivity analysis,yield and reactive N losses were most sensitive to sowing date and N application rate.When the fertilizer N application was 180kg/ha,both the maize and wheat achieved the highest yields.And the grain yields would not increase with increasing the N application rate.EI treatment could be further optimized,such as adjusting the winter wheat sowing date to around October 10 and the tilling depth to 5 cm.These practices could further increase grain yield by 2.9% and reduce reactive N losses by 10.5%.In summary,Ecological Intensification management maintain crop yields,reduce N fertilizer inputs,increase N use efficiencies,increase soil C and N sequestration,reduce C and N environmental losses,and increase net income through combination of optimal nutrient management and other advanced agronomy practices.It is a sustainable management system that can harmonize the benefits of agronomy,economy,and environment.