Effects Of Slow And Controlled Release Fertilizer Combined With Straw On Soil Enzyme Activity,NH₃ Volatilization And Greenhouse Gas Emission

The weak ability of soil nitrogen supply and retention in the wheat producing areas in the middle and lower reaches of the Yangtze River leads to the low nitrogen use efficiency of wheat,and the unit yield is far lower than the national average level,how to effectively improve the wheat yield in this area is a severe challenge.Slow and controlled release fertilizer has been proved to improve the efficiency of nitrogen use and crop yield.Meanwhile,with the high yield of crops and the intensive use of land,a large amount of straw is produced.The application of slow and controlled release fertilizer and straw returning have become important agricultural management measures to improve soil fertility and crop productivity.The combined application of slow and controlled release fertilizer and straw regulates the soil C / N ratio,affects straw decomposition,organic nitrogen mineralization and mineral fixation,and then affects soil NH₃ volatilization and N₂ O emission.The combined application of slow and controlled release fertilizer and straw lacks sufficient understanding of the process of soil fertility,NH₃ volatilization and N₂ O emission.Therefore,we studied the effects of combined application of slow and controlled release fertilizer and straw on soil fertility,nitrogen gas release and greenhouse through incubation experiment.There were 9 treatments in the incubation experiment:（1）No nitrogen application and no straw returning treatment（CK）,（2）urea（U）,（3）urea + straw（US）,（4）humic acid（HA）,（5）humic acid + straw（HAS）,（6）loss control fertilizer（LCU）,（7）loss control fertilizer + straw（LCUS）,（8）nanoFeIII-tannic acid-modified polyacrylate-coated urea（NWU）,（9）nano-FeIII-tannic acidmodified polyacrylate-coated urea + straw（NWUS）.The nitrogen application rate was240 kg N ha-1,and the straw returning rate was 3000 kg ha-1.The main research results are as follows:（1）Under the condition of single application of nitrogen fertilizer and combined application of nitrogen fertilizer and straw,compared with urea treatment,the application of slow and controlled release fertilizer increased the concentrations of NH₄⁺-N and soluble nitrogen in soil at the later stage of incubation,and decreased the NO₃^--N concentration in the whole incubation process.Meanwhile,the combined application of slow and controlled release fertilizer and straw further increased the concentrations of NH₄⁺-N and soluble nitrogen and decreased the NO₃^--N concentration in soil.Combined application of nitrogen fertilizer and straw increased soil total nitrogen,organic carbon and p H.（2）Under the condition of single application of nitrogen fertilizer and combined application of nitrogen fertilizer and straw,compared with urea treatment,the activities of soil urease,catalase and invertase were increased and soil fertility was improved by slow and controlled release fertilizers.（3）Under the condition of single application of nitrogen fertilizer,compared with U treatment,the cumulative of NH₃ volatilization and N₂ O emissions in HA,LCU and NWU treatments decreased by 9.1%,12.1%,16.3% and 13.5%,19.8%,41.6%,respectively.Under the condition of combined application of nitrogen fertilizer and straw,compared with US treatment,the cumulative of NH₃ volatilization in HAS,LCUS and NWUS treatment decreased by 9.9%,23.1% and 31.1%respectively,among which LCUS and NWUS treatment reached a significant level,the cumulative of N₂ O emissions decreased by 5.1%,9.4% and19.9%,respectively.Compared with the single application of nitrogen fertilizer treatment,nitrogen fertilizer combined with straw treatment increased the cumulative of NH₃ volatilization and N₂ O emissions by 3.2%-25.1% and 110.5%-189.7%,respectively.Nitrogen fertilizer type and straw had significant effects on NH₃ volatilization and N₂ O emission,and there was no interaction between them.（4）The total loss of gaseous nitrogen is mainly NH₃ volatilization.Under the condition of single application of nitrogen fertilizer,compared with urea treatment,slow and controlled release fertilizer treatment reduced the total loss of gaseous nitrogen by 10.2%-18.4%.Under the condition of combined application of nitrogen fertilizer and straw,the total loss of gaseous nitrogen in HA,LCU and NWU treatment decreased by 10.8%,25.0% and 33.7% respectively.Compared with the single application of nitrogen fertilizer treatment,nitrogen fertilizer combined with straw treatment increased the total loss of gaseous nitrogen by 5.1%-29.2%.（5）The total greenhouse gas warming potential of NH₃ volatilization,N₂ O and CO₂ emissions was calculated,and CO₂ emissions dominated the total greenhouse gas warming potential.There was no significant difference in total greenhouse gas warming potential between different treatments under the condition of single application of nitrogen fertilizer.Under the condition of combined application of nitrogen fertilizer and straw,compared with US treatment,HAS treatment significantly increased total greenhouse gas warming potential by 8.1%,while LCUS and NWUS treatment significantly reduced total greenhouse gas warming potential by10.2% and 12.2%,respectively.Compared with the single application of nitrogen fertilizer treatment,nitrogen fertilizer combined with straw treatment increased the total greenhouse gas warming potential by 65.0%-88.0%.Nitrogen fertilizer type and straw had significant effects on total greenhouse gas warming potential,and there was significant interaction between them.In conclusion,nitrogen fertilizer combined with straw increased the loss of gaseous nitrogen,but increased the level of soil enzyme activity and soil fertility.Under the condition of single application of nitrogen fertilizer and combined application of nitrogen fertilizer and straw,the application of slow and controlled release fertilizer can reduce soil NH₃ volatilization and N₂ O emission,while the application of LCU and NWU can reduce total greenhouse gas warming potential.Since HA increases CO₂ emissions during incubation,resulting in increased total greenhouse gas warming potential.This study provides a theoretical basis for guiding the wheat producing areas in the middle and lower reaches of the Yangtze River to apply fertilizer reasonably,make effective use of straw resources,improve soil fertility,reduce the loss of gaseous nitrogen and reduce the harm to the environment.