Simulation Study On Soil Organic Carbon And Crop Yield Under Straw Returning Based On DNDC Model

Organic carbon in farmland soil can not only provide nutrients for crops,but also maintain a good soil structure.However,it is particularly susceptible to farmland management measures.The measures of returning straw to the field,on the one hand,alleviates the waste of resources and environmental pollution,on the other hand,it supplements the soil with carbon,which is used to decompose to obtain organic carbon.If the long-term effects of straw returning to the field on soil fixed organic carbon and crop yield increase are clarified,it is of great significance to guide the improvement of farmland soil and the high and stable crop yield.This study set up a long-term positioning experiment under the wheat-jade rotation system in Guanzhong area in October 2011.The experiment used a random block design encompassing different straw returning treatments[no straw returning?S0?,half straw returning?S0.5?,and full straw returning?S1?]as main treatments,and different fertilizer applications[no fertilization?F0?,20%fertilizer reduction?F0.8?,and conventional fertilization?F1?]as sub-treatments.The design was used to analyze the effects of each treatment on soil physical and chemical properties and crop yield.Then combined with DNDC model,the response of soil organic carbon and crop yield to long-term straw returning treatment was analyzed.The results are as follows:1. Effects of straw return treatment and fertilization treatment on soil physical and chemical properties and crop yield:?1?Measures of returning straw to the field not only has obvious soil water retention effect,but also can balance and increase the soil temperature.?2?Farmland inorganic nitrogen content and NH₃ emissions are proportional to the amount of fertilizer applied.Compared with fertilization alone,fertilization+straw return treatment can significantly reduce the cumulative ammonia emissions by 4.34?6.38 kg·hm-2,ammonia loss rate 1.21%?1.55%,and inorganic nitrogen 5.56%-31.36%.Among them,the treatment effect of returning straw to field+reducing fertilization is the best.?3?Both straw and fertilization can significantly increase soil organic carbon storage of 0-50cm,of which S1F0.8 treatment is the best.?4?Returning straw to the field only has a significant yield increase effect with fertilization,in which summer maize and winter wheat yields increase by 6.23%-20.21%,16.60%?28.17%,respectively.But the difference between the two straw return treatments is not obvious,and the difference between the two fertilization treatments is also not obvious.Based on the above conclusions,it can be concluded that returning straw to the field+reducing fertilization can improve the physical and chemical properties of the soil and increase the yield of crops.2. Based on the DNDC model,the simulation prediction of soil organic carbon and crop yield under long-term straw return to the field:the three treatments of S0F0.8,S0.5F0.8,and S1F0.8 are the research objects.The result shows:?1?The relative root-mean-square error?RRMSE?of the simulated and measured values of the soil water heat,soil organic carbon,and crop yield indicators in the model ranges from 6.61-27.75%,and the determination coefficient?R²?ranges from 0.5-0.96,and the correlation analysis results are all related or significant correlation,which shows that the model can better simulate the characteristics of soil organic carbon and crop yield in this area.?2?In the next 50 years:if straw is not returned to the field,soil organic carbon storage will decrease year by year,and will eventually decrease by 1.20%from the original.If straw is returned to the field continuously,the storage of soil organic carbon and the fixed carbon capacity of the soil will increase year by year and will be proportional to the amount of returned fields.After 50 years,the organic carbon reserves treated by S0.5F0.8 and S1F0.8 have increased by 27.31%and 51.10%respectively.The treatment of returning straw to the field is helpful for high and stable crop yields,and the effect of increasing yield is best when the straw is continuously returned to the field for 10-20 years.To sum up,long-term full straw return+reduced fertilization treatment is an effective management model for realizing farmland soil to improve carbon sequestration capacity,enhance soil quality and ensure high and stable crop yields.