Study Of Straw Mulching And Nitrogen Fertilization On Soil Fertility,N₂O,NH₃ And CH₄ Emission Intensity In Maize And Soybean Cropping System

Straw mulching and scientific nitrogen application can effectively improve soil nutrient and nitrogen utilization rate,which is of great significance to promote farmland green production.Guanzhong plain,Shaanxi province,China is the main grain producing area,but the long-term unsuitable nitrogen application level and production measures make the farmland nitrogen utilization rate change greatly,the soil nutrient level is poor,and the greenhouse gas emission also shows an obvious upward trend,which seriously threatens the‘food-soil-ecology’safety in this area.Therefore,this study continues the long-term field experiment of straw mulching and fertilization in the North Campus of Northwest Agriculture and Forestry University（2011till now）.Based on the conventional‘winter wheat-summer maize’and‘winter wheat-summer soybean’one-year double cropping multiple cropping system,taking summer maize and summer soybean as the research objects,using the split plot experimental design,set two straw mulching levels（NS,no straw mulching;S,straw mulching）and three nitrogen application levels（F0,no nitrogen application;F,conventional nitrogen application;F0.8,reduced nitrogen application）,a total of six treatments（NSF0,no straw mulching+no nitrogen application;NSF,no straw mulching+conventional nitrogen application;NSF0.8,no straw mulching+reduced nitrogen application;SF0,straw mulching+no nitrogen fertilizer;SF,straw mulching+conventional nitrogen application;SF0.8,straw mulching+reduced nitrogen application）.By analyzing the indexes of the soil nutrients,NH₃,N₂O and CH₄ emission intensity,nitrogen utilization rate and crop yield,the straw mulching+nitrogen application measures suitable for farmland fertilization,crop yield increase and environmental and economic benefits in Guanzhong plain were finally determined.The main results are as follows:（1）Straw mulching combined with nitrogen fertilizer can significantly improve the yield of maize and soybean.The yield of reduced nitrogen and conventional nitrogen application increased significantly by 17.82%-21.29%and 21.39%-23.73%（maize）,42.94%-54.42%and 48.80%-60.05%（soybean）compared with no nitrogen application,but there was no significant difference between them.Under the same nitrogen application level,straw mulching significantly increased the maize,and soybean yield by 6.43%-7.62%and 8.77-13.71%compared with no mulching,respectively.（2）Reduced nitrogen and conventional nitrogen treatments significantly increased nitrogen accumulation of maize and soybean plants,but there was no significant difference between them.Under the same nitrogen application level,straw mulching significantly increased the aboveground nitrogen accumulation of maize.Compared with conventional nitrogen application,reduced nitrogen application increased nitrogen partial productivity（PEPN）and nitrogen agronomic utilization efficiency（AEN）,and there was a significant difference in maize production between the two seasons.Nitrogen use efficiency（NUE）showed SF0.8>SF1>NSF>NSF0.8.Under different nitrogen application treatments,straw mulching could significantly improve PEPN,AEN and NUE of the summer maize and soybean.（3）The contents of soil ammonium nitrogen and nitrate nitrogen in nitrogen fertilizer treatment at different growth stages of maize and soybean showed a‘single peak’curve,and there was no difference in no nitrogen fertilizer.Meanwhile compared to NSF0.8treatment,SF0.8 significantly increased the nutrient of soil total nitrogen（3.91%-4.82%）,total phosphorus（3.73%-9.87%）,available phosphorus（5.01%-20.54%）and organic matter（3.30%-13.57%）.（4）The NH₃ emission rate of nitrogen fertilizer treatment at different growth stages of maize and soybean showed a‘single peak’curve,and there was no obvious fluctuation in the treatment without nitrogen fertilizer;The NH₃ emission rate was basically the third or fourth day after the application of nitrogen fertilizer in maize,reached the peak on the second day after the application of nitrogen fertilizer in soybean,and decreased to the level before the application of nitrogen fertilizer 15 days after the application of nitrogen fertilizer.Straw mulching could reduce NH₃ emission rate,and there was significant difference between S and NS treatments within 15 days after nitrogen application.The cumulative ammonia emission during growth period was lower under SF0.8 treatment and significantly decreased by 7.34%-10.25%compared with NSF treatment.（5）Nitrogen application and straw mulching can reduce the CH₄ uptake rate of crops,but significantly increase the cumulative emissions of N₂O during the growth period of crops.At different growth stages of maize and soybean,the change of N₂O emission rate of each treatment is basically consistent with that of NH₃.In the late growth stage of maize and the middle growth stage of soybean,the N₂O emission rate of SF0.8 was significantly higher than that of NSF0.8 treatment by 3.55-14.39μg·m^-2·h^-1and 3.06-8.29μg·m^-2·h^-1,respectively.The net greenhouse gas emission（NGHG）of SF0.8 treatment increased significantly by 5.40%-11.48%compared with NSF,but the net greenhouse gas emission intensity（NGHGI）decreased significantly or had no significant difference.In conclusion,‘straw mulching+reduced nitrogen application（SF0.8）’treatment can effectively improve soil nutrient status,maintain high yield and significantly reduce farmland CH₄ emission intensity.It can be used as a sustainable production measure to ensure soil fertilization and crop yield increase in Guanzhong plain with ecological and economic benefits.