Effect Of Mixed Controlled-release Urea Reduction On Soil Carbon And Nitrogen Emissions And Its Impact Mechanism

To explore controlled-release nitrogen fertilizer mixed with common urea application on dryland soil carbon and nitrogen emission characteristics and it's effect mechanism.This paper use the ¹⁵N isotope labeling techniques,and a pot experiment with corn was conducted to demonstrate the characteristics of ammonia volatilization,nitrogen oxide emission,carbon dioxide emission and methane emission from soil treated with controlled-release nitrogen fertilizer mixed with urea and reduction of nitrogen fertilizer.This paper also studies different forms of soil carbon and nitrogen by different treatments.And studies soil carbon and nitrogen emission characteristics and it's impact mechanism.The results are as follows:?1?Soil ammonia volatilization mainly occurred in the first two weeks after fertilization and it was the main form of nitrogen loss.The cumulative amounts of ammonia volatilization were:nitrogen free treatment?CK?3.69 kg/hm²,normal urea fertilization?NU?18.64 kg/hm²,controlled release nitrogen fertilizer mixed with urea?PU1?9.39 kg/hm²,reduction of mixed nitrogen fertilizer?PU2?6.44 kg/hm²,reduction of mixed nitrogen?PU3?5.02 kg/hm²,respectively.Compared with normal urea,the controlled release nitrogen fertilizer can significantly reduce the ammonia volatilization loss,and the reduction amount is about 50%of the ammonia volatilization loss from normal urea treatment.The application of controlled release nitrogen fertilizer reduction can significantly reduce the ammonia volatilization loss of soil nitrogen,which is 31.5%and 46.5%less than the controlled release respectively.There was a significant positive correlation between fertilizer application and soil ammonia volatilization loss and the Pearson correlation coefficient was0.945.?2?Soil nitrous oxide emissions occur during the whole growth period of maize and the peaks of nitrous oxide flux is concentrated between 55 and 91 days after fertilization.The cumulative emission of nitrous oxide from soil is CK 1.52 kg/hm²?NU 1.76 kg/hm²?PU1 1.81 kg/hm²?PU2 1.61 kg/hm²?PU3 1.52 kg/hm²,respectively.Compared with normal urea,the controlled release nitrogen fertilizer could not significantly reduce the amount of nitrous oxide from soil,and the controlled-release of nitrogen fertilizer had a certain inhibitory effect on the total emission of nitrous oxide but not reach the significant.The results indicated that N₂O emission in different fertilizer treatments had an obvious daily variation law with the maize growth.The emission rate begins slowly and reached their maximum values in the middle stage and trend to be stable at last.?3?Soil CO₂ emission in dryland is the main form of carbon gas loss,and soil CH₄emission remains extremely low in the whole growth of maize.Cumulative emissions of soil CO₂ were CK 5045.08 kg/hm²,NU 5936.82 kg/hm²,PU1 5824.86 kg/hm²,PU2 5606.56 kg/hm²,PU3 5231.35 kg/hm²,respectively.The speed of soil CO₂emissions and CH₄ emission rate are opposite.The emission of soil CO₂ increases with the increase of nitrogen fertilizer,and the application of controlled-release nitrogen fertilizer has no significant effect on CO₂ emission reduction.The reduction of nitrogen can significantly reduce the total CO₂ emissions of soil which is beneficial to the accumulation of soil organic carbon.?4?Application of nitrogenous fertilizer to soil can significantly improve the content of total dissolved nitrogen?TDN?and fixed ammonium in soil,among which the increase of normal urea treatment and controlled-release nitrogen fertilizer treatment on TDN is 21.5%and 63.2%respectively.And the increase of normal urea treatment and controlled-release nitrogen fertilizer treatment on fixed ammonium is 33.5%and26.9%respectively.The reduction of fertilization can significantly reduce the fixed ammonium thus reducing the holding effect on nitrogen of soil.Compared with common urea,controlled-release nitrogen fertilizer can significantly increase soil organic carbon content and increase soil carbon retention.?5?The controlled-release nitrogen fertilizer cannot significantly increase maize yield compared with normal urea.The reduction of fertilization will not lead to the decrease of maize yield,but can significantly increase the utilization rate of nitrogen fertilizer.The PU2 treatment has the highest maize yield and nitrogen use efficiency which are 266.45g/pot and 52.21%.Therefore,use controlled-release nitrogen fertilizer reduction is a more efficient and environment-friendly fertilizer application.