Effect Of Controlled Release Blend Bulk Urea On The Soil Nitrogen Supply And Soil Enzyme Activity In Wheat And Rice Fields

Soil nitrogen supply and rational application of nitrogen fertilizer play an important role in increasing crop yield and nitrogen utilization rate.Controlled-release nitrogen fertilizer(CRNF)can meet the demand of nitrogen for crops more effectively than common urea(UR),effectively promote the growth and development of crops,but due to its high price,farmers are generally not easy to accept,and it is relatively limited to be used in large areas.Therefore,the use of controlled release nitrogen fertilizer blended urea fertilization method is expected to achieve the full crop growth period of nitrogen coordination,reduce costs and improve economic efficiency.At present,research at home and abroad mainly focuses on the effects of controlled-release nitrogen fertilizer blended urea on crop growth,yield,and nitrogen use efficiency.However,there are few reports on the key conversion enzymes of soil nitrogen and nitrogen as a whole.The study of the mechanism of action is even more lacking.Therefore,in this paper,the field experiment of rice-wheat rotation was conducted under the conditions of 150 kg/hm~2 nitrogen application rate.One-time base application of 0,10%,20%,40%,80%,100%controlled-release nitrogen fertilizer was used to blend urea,focusing on the changes in nitrogen forms and contents of soil nitrogen and the key conversion enzymes of nitrogen under controlled release urea conditions,with a view to seeking appropriate controlled-release blended urea to achieve the objective of increasing soil nitrogen supply capacity and promoting crop growth.The main findings are as follows:(1)The application of suitable controlled-release nitrogen fertilizer promoted soil urease and protease activity during the mid-late growth stage of wheat and rice,and nitrate reductase activity in the later stage of wheat growth,thereby delaying the peak period of ammonium nitrogen in rice,providing sufficient nitrate nitrogen for wheat and reducing the nitrogen loss,significantly incrasing the soil inorganic nitrogen and soil microbial biomass nitrogen content.The addition of 20%to 100%controlled-release nitrogen fertilizer significantly increased the ammonium nitrogen content in the jointing-mature stage of rice by 0.90 to 5.10 mg/kg,and increased the microbial biomass nitrogen content at booting-maturity by 4.63 to 12.57 mg/kg(wheat)and 1.39~5.43mg/kg(rice).The addition of 40%to 100%controlled-release nitrogen fertilizer significantly increased the nitrate nitrogen level at booting-maturing stage by 9.86~43.24mg/kg(wheat)and 1.13~3.94mg/kg(rice),and the available nitrogen at jointing-mature stage by 6.78~24.24mg/kg(wheat)and 5.10~13.10mg/kg(rice).Blending 40%to 100% controlled-release nitrogen fertilizers increased soil urease activity by 36.09%to 86.57%(wheat)and 7.07%to 31.82%(rice)at jointing and booting stage,meanwhile increasing the protease activity by 6.85%to 42.85%(wheat)and 7.69%to 26.63%(rice).The nitrate reductase activity in the booting-maturity period was increased by 5.92%~33.33%(wheat)and 8.32%~84.38%(rice).(2)Blending appropriate controlled-release nitrogen fertilizer significantly increased the above-ground dry matter and nitrogen accumulation of wheat and rice crops,improved agronomic traits,and promoted grain yield and income.The yield and profit of the 40%controlled-release nitrogen fertilizer was the best,followed by blending 20%.The addition of 20%to 100%controlled-release nitrogen fertilizer compared with UR significantly increased the above-ground dry matter accumulation in the jointing-mature stage by2.81%to 15.09%(wheat)and 3.90%to 11.90%(rice),but the distribution ratio of dry matter and nitrogen in the panicle of crops under the addition of 80%to 100%controlled-release nitrogen fertilizer was significantly lower.The 40%controlled-release nitrogen fertilizer mixed with 60%urea treatment could significantly improve the panicle length and flag leaf area(wheat),and the number of grains per spike,1000-grain weight,seed-setting rate,flag leaf length and flag leaf area(rice),and the agronomic traits,yield,and the economic benefits were all optimal of wheat and rice.compared with UR,the yield of wheat increased by 14.23%and for rice,by 10.93%.Compared with UR,the yield of wheat increased by 14.23%and for rice,by 10.93%.(3)With the increasing CRNF addition ratio,the nitrogen partial productivity(NPP),nitrogen agronomy efficiency(NAE),nitrogen uptake efficiency(NUPE),nitrogen apparent utilization efficiency(NAUE)increased both in wheat and rice at beginning and decreased afterwards,with the peak in the treatment of the 40%controlled release nitrogen fertilizer mixed with 60%urea treatment.Compared with UR,the NPP,NAE,NUPE,NAUE of wheat and rice incrased by 14.21%,27.26%,17.50%,29.89%and 10.93%,73.72%,19.15%,53.09%,respectively.The nitrogen harvest index(NHI)was the lowest at 100%controlled release nitrogen fertilizer.Compared with UR,the NHI decreased by 3.99%(wheat)and 8.51%(rice),respectively.The contribution rate of soil nitrogen(CRSN)declined first and then rose with the increase in blending ratio,and 40%controlled release nitrogen fertilizer mixed with 60%urea was the lowest.Compared with UR,the CRSN decreased by 14.38%(wheat)and 15.84%(rice),respectively.In summary,one-time base application of 20%to 40%controlled-release nitrogen fertilizer could increase soil N supply,soil enzyme activity,crop growth,yield,and nitrogen use efficiency,saving time and effort.The treatment of 40%controlled release nitrogen fertilizer mixed with 60%urea could release the appropriate soil N supply,significantly increase the yield and economic benefit.The potential for future of popularization and application in the future is great.