Effects Of Nitrogen Reduction Combined With Urease/Nitrification Inhibitors On Nitrogen Loss And Nitrogen Use Efficiency In Purple Soil-wheat System

With the increase of nitrogen fertilizer application,the economic benefit of agricultural production decreased gradually,nitrogen loss increased and nitrogen use efficiency decreased,caused serious waste of resources and ecological environment damage.Purple soil is an important cultivated soil in southwest China.Many scholars have explored the measures to increase the efficiency of nitrogen reduction,however,what is the effect of urease/nitrification inhibitors on nitrogen loss and utilization efficiency of purple soil-dryland crop systems?What are the influencing factors?Relevant studies are relatively lacking..In this study,purple soil of different pH in Sichuan was taken as the object to carry out wheat pot experiment,and each purple soil was treated with 6treatments:（1）control treatment without nitrogen fertilizer（CK）;（2）conventional nitrogen fertilizer dosage treatment（CN）;（3）nitrogen fertilizer minus treatment（RN,2/3CN）;（4）nitrogen fertilizer+urease inhibitor treatment（RN+UI）;（5）nitrogen fertilizer+biological nitrification inhibitor treatment（RN+BNI）;（6）nitrogen fertilizer+two inhibitors treatment（RN+BNI+UI）.The effects of these treatments on nitrogen loss（ammonia volatilization,inorganic nitrogen leaching）and nitrogen use efficiency（yield,crop nitrogen uptake,soil residual nitrogen）of wheat in different purple soil-wheat systems were studied.In addition,Meta-analysis was used to quantitatively evaluate the overall effects of urease/nitrification inhibitor on nitrogen loss and nitrogen use efficiency in dryland farmland system in China,and to reveal the soil,crop and environmental factors that affect the differences of urease/nitrification inhibitor application effects in dryland farmland in China.In order to provide scientific basis for the practical application of urease/nitrification inhibitors in different purple soil crop systems in Sichuan and Chongqing area..The main conclusions are as follows:The results of pot experiment showed that:（1）The ratio of nitrogen whereabouts in different purple soil-wheat systems was different.Calcareous purple soils-wheat system:wheat nitrogen uptake（45.23%）>ammonia volatilization（18.30%）>soil residual nitrogen（15.84%）>nitrogen leaching（3.59%）.Acidic purple soils-wheat system:wheat nitrogen uptake（45.94%）>ammonia volatilization（16.35%）>soil residual nitrogen（16.31%）>nitrogen leaching（2.78%）.The ratio of nitrogen absorption and soil residual nitrogen to nitrogen application in acidic purple soil wheat was higher than that in calcine purple wheat,while the ratio of ammonia volatilization and nitrogen leaching in acidic purple soil wheat was lower than that in calcine purple soil.（2）Effects of nitrogen reduction combined with urease/biological nitrification inhibitors on nitrogen loss in different purple soil-wheat systems was different.In the calcareous purple soil-wheat system,RN+UI treatment could reduce NH₃ volatilization by24.6%.In the acidic purple soil-wheat system,RN+UI treatment could reduce NH₃volatilization by 28.02%,followed by RN+BNI+UI treatment which could reduce NH₃volatilization by 26.1%.RN+BNI treatment,and RN+BNI+UI treatment had a good effect on reducing nitrogen leaching in calcareous purple soil and acidic purple soil,but the difference was not significant（P>0.05）.Application of urease/nitrification inhibitor could significantly reduce soil residual nitrogen content,but there was no significant difference between single application and combined application（P>0.05）.（3）Effects of nitrogen reduction combined with urease/biological nitrification inhibitors on nitrogen utilization in different purple soil-wheat systems was different.The yield and nitrogen absorption of wheat in acidic purple soil were higher than that in calcareous purple soil,and the nitrogen utilization rate of wheat in calcareous purple soil was higher than that in acidic purple soil.RN+BNI+UI treatment in acidic purple soil significantly increased wheat yield by 16.75%（P<0.05）.In acidic purple soil,RN+BNI+UI treatment significantly increased nitrogen agronomic efficiency by 33.36%（P<0.05）.Compared with conventional nitrogen treatment,all nitrogen reduction+inhibitor treatments had significant improvements in nitrogen apparent use efficiency and agronomic use efficiency（P<0.05）.In conclusion,Considering the purpose of reducing nitrogen loss and promoting stable yield,the application mode of 2/3 conventional nitrogen application rate(200 kg N·ha^-1)+urease inhibitor is recommended for wheat planting in calcine purple soil.The application mode of 2/3 conventional nitrogen(200 kg N·ha^-1)+biological nitrification inhibitor+urease inhibitor is recommended for wheat planting in acidic purple soil.The results of Meta-analysis showed that:（1）Compared with the application of nitrogen fertilizer alone,nitrogen fertilizer combined with urease/nitrification inhibitor could increase the yield of dryland crops by16.68%,increase the nitrogen utilization rate of dryland crops by 27.6%,reduce ammonia volatilization by 27.06%,and reduce nitrogen leaching amount by 37.17%.（2）Nitrogen fertilizer combined with urease/nitrification inhibitors showed different field effects on different crop types.Maize showed higher yield（increased yield by 26.2%）and nitrogen utilization rate（increased nitrogen utilization rate by 44.44%）,vegetable land had the best effect on reducing ammonia volatilization（reduced ammonia volatilization amount by 40.19%）,and wheat land had better effect on reducing nitrogen leaching amount（reduced nitrogen leaching amount by 43.07%）.（3）Nitrogen fertilizer+urease inhibitor could increase crop yield by 24.46%,nitrogen fertilizer+nitrification inhibitor could increase crop nitrogen utilization rate by32.25%,nitrogen fertilizer+urease inhibitor could reduce ammonia volatilization by47.23%,nitrogen fertilizer+urease inhibitor+nitrification inhibitor could reduce ammonia volatilization by 51.94%.Nitrogen fertilizer+nitrification inhibitor signficantly reduced nitrogen leaching by 42.39%in dryland fields.The single application of urease inhibitor and nitrification inhibitor was better than the combined application.（4）Soil pH has a great influence on the effect of nitrification inhibitors and urease inhibitors.When soil pH<6.5,nitrogen fertilizer combined with urease/nitrification inhibitor could increase crop yield by 24.51%and nitrogen utilization rate by 44.77%.The higher the soil pH value,the stronger the ammonia emission reduction effect,and the highest reduction of ammonia volatilization was 33.75%;When soil 6.5<pH<7.5,nitrogen fertilizer combined with urease/nitrification inhibitor had the strongest effect on reducing nitrogen leaching amount,which could significantly reduce nitrogen leaching amount by48.51%.In summary,this study revealed that urease/biological nitrification inhibitors had different effects in regulating nitrogen loss and nitrogen use efficiency in purple soil-wheat systems with different pH,and verified the feasibility of reducing nitrogen fertilizer amount,increasing efficiency and stabilizing yield in purple soil.Further Meta analysis revealed that crop species,soil pH and single and combined application of inhibitors were important factors affecting the regulation effect of urease/nitrification inhibitors on farmland nitrogen loss and crop yield in dryland in China.It can be inferred that in the practical application of urease/nitrification inhibitors in purple soil farmland systems,the crop type,application method and purple soil pH should be considered.The above research results can provide important scientific basis for fertilizer reduction and scientific fertilization in purple soil farmland.