Dynamic Analysis And Nitrogen Application Simulation On N₂O Emission From Wheat-Maize Farmland In Huang-Huai-Hai Region

Nitrous oxide?N₂O?is a greenhouse gas with a long time and great potential.However,about1.5 million tons of N₂O are discharged into the atmosphere every year due to the application of chemical nitrogen fertilizer,accounting for 44%of the N₂O released into the atmosphere by human activities every year.The twin-cropping system of wheat-summer maize is regarded as a successful example of intensive agricultural system,and the input of resources such as nitrogen fertilizer in production not only improves the crop productivity of wheat-maize rotation system,but also generates and emits a large amount of greenhouse gases such as N₂O.In particular,excessive nitrogen fertilizer is the main driving factor of N2O emission in farmland soil.As one of the main farmland management measures,straw returned has been widely concerned and applied in agricultural production practice.However,the effect of straw returned on N₂O emission in farmland soil is still controversial.Therefore,it is necessary to further study the effect of different straw returned and the amount of straw returned on N₂O emission in wheat-maize rotation system,and to clarify the effect and size of factors such as nitrogen application under straw returned and crop growth.In this study,field experiments were conducted to quantitatively analyze the effects and interactions of factors such as straw returned amount,crop growth,and nitrogen application amount under straw returned amount on N₂O emission in farmland soil,and explore the ways of controlling and reducing N₂O emission under straw returned amount through the combination of models.This study conducted from 2013 to2017 in Daiyue experimental station of Shandong Agricultural University and State Key Laboratory of Crop Biology,and experienced four full wheat-maize anniversaries.Five different straw returned treatments?No returned,25%returned,50%returned,75%returned and 100%returned?were set under the condition of traditional fertilizer application,and five nitrogen mulching treatments?N0,N1,N2,N3 and N4?with excessive nitrogen application were set under the condition of full straw returned,and no crops were set for each treatment.The main research results are as follows:1.Effects of straw returned on N₂O emission from farmland soil.With the increase of straw returned amount,the change trend of N₂O cumulative emission in wheat season and maize season was consistent,both showed an increase trend,and the increase rate in maize season was greater than that in wheat season.From C0 to C100,the cumulative N₂O emission in wheat season was 1.01-1.74 kg ha^-1,1.04-1.83 kg ha^-1,1.07-1.93 kg ha^-1,1.09-2.01 kg ha^-1 and 1.11-2.06 kg ha^-1,respectively,with no significant difference between treatments.The cumulative N₂O emission in maize season was 3.78-6.60 kg ha^-1 treated with C0,which was significantly lower than 3.91-8.77 kg ha^-1 treated with C25-C100.With the increase of straw returned amount,the effect of straw returned amount on farmland N2O emission?SIP?gradually increased.From C0 to C100 treatment,SIP increased by 2.98-8.23%,2.38-7.73%,2.43-6.81%and 1.65-5.96%for each 25%increase of straw returned amount.With the development of the anniversary of straw returned to farmland,SIP also presents an increasing trend.From C0 to C100,the annual SIP were 2.98-9.43%,4.10-12.74%,7.23-26.17and 8.22-28.73%for 2013-2014,2014-2015,2015-2016 and 2016-2017.The effect of non-returning straw and different returning amounts on N₂O emission in wheat season was not significant,and the effect of different returning amounts on N2O in maize season was not significant,but significantly greater than that of non-returning.On the whole,straw returned increased N₂O emission from wheat-maize annual farmland soil,but the operating space to reduce N2O emission of farmland by reducing straw returned amount was small and the effect was not obvious.2.Effects of crop growth on N2O emission from farmland soil under different straw returned capacity.Compared with farmland without planting crops,crop growth reduces N₂O emission from farmland soil.From C0 to C100,the N2O emission of wheat growth decreased by 0.08-0.26 kg ha^-1,0.09-0.32 kg ha^-1,0.10-0.38 kg ha^-1,0.12-0.45 kg ha^-1 and 0.13-0.51 kg ha^-1,respectively.Maize growth reduced N₂O emissions of 0.70-0.83 kg ha^-1,0.82-1.17 kg ha^-1,0.97-1.54 kg ha^-1,1.13-1.88 kg ha^-1 and 1.34-2.33 kg ha^-1,respectively.With the increase of straw returned amount,the decrease of cumulative N₂O emission from crop-growing farmland soil was gradually increased,compared with that without crop-growing soil under the same mulching amount.Under the condition that straw was not returned to the field,the absolute value of the influence rate?GIP?of wheat and maize growth on N2O emission in farmland soil was 7.20-13.53%and 10.86-15.60%,respectively.With the development of the growth period,GIP tends to increase,and its size has a significant linear correlation with the amount of farmland returned.3.Effects of straw returned and nitrogen application on N₂O emission in farmland soil.The change trend of N₂O cumulative emission in wheat season and maize season was consistent with the increase of N application,but the effect of n application on N2O emission in maize season was significantly greater than that in wheat season.In N0-N4 treatment,the cumulative N₂O emission in wheat season was 0.66-1.43 kg ha^-1,0.89-1.66 kg ha^-1,0.99-2.10kg ha^-1,1.17-2.44 kg ha^-1 and 1.41-2.67 kg ha^-1,respectively.The cumulative N₂O emission in maize season was 0.34-0.71 kg ha^-1,2.84-7.67 kg ha^-1,4.98-10.61 kg ha^-1,7.21-21.29 kg ha^-1and 8.60-29.21 kg ha^-1,respectively.Under the same nitrogen application level,the N₂O emission coefficient of nitrogen fertilizer showed significant differences in different wheat seasons,maize seasons and years,respectively 0.12-0.42%,1.30-4.48%and 0.94-3.15%.From N0 to N4,the N₂O emissions per unit biomass and per unit yield were 0.04-1.30 g kg^-1 and0.09-2.68 g kg^-1,respectively,and the N₂O emissions per unit biomass and per unit yield in the maize season were greater than that in the wheat season in the same year.The influence rate?NIP?of nitrogen application on N₂O emission in farmland soil increased linearly with the increase of nitrogen application.4.Effects of straw returned under nitrogen application on crop growth and N₂O emission.Under straw returned,the influence of crop growth on N₂O emission rate?GIP?of farmland soil was significantly correlated with biomass and N uptake.Nitrogen application promoted the growth and yield of crops.Nitrogen application,crop growth period and their interactions were significantly correlated with crop biomass and nitrogen uptake,as well as N₂O emission.Wheat growth can significantly affect N2O cumulative emission in wheat season.There is a significant correlation between N₂O cumulative emission in maize season and nitrogen uptake and yield of maize,and there is a significant correlation between N2O cumulative emission and biomass of maize.The effect of crop growth on soil N₂O emission was significantly correlated with nitrogen absorption,and soil nitrogen was also significantly correlated with soil N₂O emission.It was found that N0 treated N₂O emission was only significantly correlated with soil NH₄⁺-N content.N₂O emissions treated with N1 and N2 were significantly correlated with NH₄⁺-N,NO₃^--N and available nitrogen content in different soil layers.N₂O emissions treated with N3and N4 were significantly correlated with NH₄⁺-N and available nitrogen content in different soil layers.And also significantly correlated with NO₃^--N content in 0-20 cm and 20-40 cm soil layers,but significantly correlated with NO₃^--N content in 40-60 cm soil layer treated with N3,and not correlated with NO₃^--N content in 40-60 cm soil layer treated with N4.5.Simulation of different nitrogenous fertilizer management scenarios by APSIM model.Under straw returned,N0 to N2 treatment,with the increase of nitrogen application,wheat and maize yield was significant,nitrogen application was greater than N2(160 kg ha^-1 in wheat season,300 kg ha^-1 in maize season)treatment,increased nitrogen application could not significantly promote the increase of crop yield,but could significantly increase N₂O emission.Combined with the model simulation,the n application threshold measured in the test can be reduced from 460 kg ha^-1 to 420 kg ha^-1(210 kg ha^-1 in wheat season and 210 kg ha^-1 in maize season)without loss of yield.Moreover,through nitrogen fertilizer regulation,the amount of fertilizer applied in wheat season was increased and the amount applied in maize season was correspondingly reduced.Under the condition that the maize yield was not significantly reduced,the annual yield was guaranteed and the N2O emission in farmland soil could be further reduced.