Effects Of Nitrogen Application Rate And Straw Returning On Summer Maize Yield And Greenhouse Gas Emission From Farmland

Straw returning and rational nitrogen application are of great significance to increase crop yield and economic benefit,improve soil structure and promote sustainable development of agricultural ecology.However,in the pursuit of sustainable high yield in production,the phenomenon of excessive fertilization is becoming more and more serious,resulting in nitrogen loss and greenhouse gas emissions posing serious challenges to the environment.The large amount of CO2produced during the decomposition of returned straw will also aggravate the greenhouse effect.In order to solve this problem,to alleviate the contradiction between nitrogen fertilizer and straw returning on crop yield and greenhouse gas emissions,and to explore the optimal combination of nitrogen fertilizer and straw returning for agricultural production and environmental friendly,a two-factor randomized block experimental design was adopted in this study.This experimental study adopts a two-factor randomized block design,setting four nitrogen application rates(0 kg hm^-2:F₀,150 kg hm^-2:F₁,225 kg hm^-2:F₂,300 kg hm^-2,F₃)and two methods of wheat straw returning to filed（wheat straw return to field:+S,wheat straw not return to field:-S）.The effects of different nitrogen application rates on soil nutrients,corn yield,nutrient absorption and utilization,and greenhouse gas emissions under the two methods of returning to the field were systematically explored.By calculating the economic and environmental benefits of the farmland,the comprehensive evaluation of the return of wheat straw to the field and the application of different nitrogen fertilizers.The impact of dosage on the ecological environment of farmland provides theoretical basis and technical support for the increase of agricultural production and efficiency,and at the same time provides a practical and reliable scientific basis for the low-carbonization of high-carbon agriculture.The main research results are as follows:（1）Under the same method of returning straw to the field,nitrogen application significantly increased the dry matter accumulation,carbon fixation and yield of summer maize,promoting the absorption of nitrogen by the maize plant,the yield and total nitrogen absorption of the plant increased respectively 28.5%-41.6%and39.9%-54.6%.The amount of carbon sequestration,total nitrogen uptake and yield of summer maize increased with the increase of nitrogen application rate when straw was not returned to the field.After straw returning treatment,with the increase of nitrogen application rate,it showed a trend of first increase and then decrease.When the nitrogen application rate was 225 kg hm^-2,the turning point reached,the excessive nitrogen application rate(300 kg hm^-2)is not conducive to plant carbon fixation,nitrogen accumulation and yield increase.Under the same nitrogen application rate,the dry matter accumulation and carbon sequestration of the straw returning treatment increased by 4.8%-9.8%and 5.5%-9.1%,the yield and total nitrogen uptake increased by 2.3%-7.1%and 3.7%-16.2%compared with non-returning mode of straw.（2）Both nitrogen application and straw returning to the field improved the soil nutrients in summer maize fields.Compared with no nitrogen application（F₀）,nitrogen application significantly increased soil available nitrogen,available potassium,total nitrogen and organic carbon,and increased with the increase of nitrogen application rate.Soil available phosphorus content decreased with the increase of nitrogen application rate.Under the same nitrogen application rate,the available phosphorus,available potassium,total nitrogen and organic carbon of straw returning to the field increased by 1.1%-7.5%、1.8%-6.1%、0.2%-2.8%and6.3%-18.7%,respectively.（3）During the summer corn growing season,the farmland soil is the source of N₂O and CO₂ and the sink of CH₄.After fertilization+rainfall/irrigation,the emission flux of N₂O and CO₂ reached the peak,and the emission flux decreased with the passage of time.The gas emission time of basal fertilizer was longer than that of topdressing.In the late summer corn growth period,there is no significant difference in greenhouse gas emission fluxes among the treatments.Under the same method of returning straw to the field,compared with no nitrogen fertilizer,nitrogen application significantly promoted the emission of N₂O and CO₂,and the cumulative emissions of N₂O and CO₂ increased by 60.1%-626.0%and 2.0%-11.4%compared with no nitrogen fertilizer,respectively.Under the same fertility level,the N₂O and CO₂ of the straw returning treatment increased by 24.0%-88.5%and 13.0%-22.2%,respectively,compared with the non-returning treatment.Nitrogen application and straw returning to the field also promoted the emission of CH₄.Under the two returning methods,the cumulative absorption of CH₄ under the four fertility levels showed F₁>F₀>F₂>F_3.Under the same nitrogen application rate,the cumulative emission of CH₄ in the treatment of returning to the field was 12.5%-23.1%higher than that in the treatment of not returning to the field.（4）The increase of greenhouse gas emissions by returning straw is less than its contribution to the crop field,and conducive to reducing the comprehensive warming potential.Excessive nitrogen fertilizer F₃ is not conducive to the comprehensive warming potential.At the same time,there is a problem of waste of resources.Through the calculation of agricultural materials,manpower input and yield income,it is known that under the same nitrogen application rate,straw returning to the field significantly increases the comprehensive farmland benefits by 10.2%-18.9%,and the F₂+S treatment has the highest comprehensive benefits.In summary,the analysis shows that by studying the effects of straw return and nitrogen fertilizer combined application on summer maize yield and comprehensive warming potential,we know that F₂+S treatment can not only obtain higher summer maize economic benefits,but also maximize the economic benefits of summer maize.Minimize the environmental risks caused by greenhouse gas emissions and have good economic-environmental benefits.Therefore,wheat straw are returned to the field and225 kg hm^-2 nitrogen fertilizer is applied,the yield of summer maize and the best environment-friendly production mode are ensured.