Abstract:

In view of the problems of excessive input of nitrogen(N)fertilizer,serious nitrogen loss and soil N accumulation,and hard to popularize controlled-release urea(CRU)because of its high cost,this research,based on the field experiment including six crop growing seasons over three years,explored the application effect of combined CRU with urea under the condition of reduced N rate in winter wheat-summer maize rotation and aimed for optimizing the N application rate under applying the optimized blending application ratio of CRU and urea,so as to provide the technical references for reducing chemical N fertilizer input,increasing its use efficiency and generalizing CRU.The experimental design consisted of six treatments:CK(No N application),FH(urea with 270-240 kg/ha N application on winter wheat and summer maize respectively;50% of the total N applied once and 50% dressing).For N1,N2,N3 and N4 treatments, mixture of CRU and urea(controlled release nitrogen accounting for 40% of the total nitrogen content) was applied once before planting at 243,216,189 and 162 kg/ha respectively for winter wheat,and was applied at 216, 192, 168, and 144 kg/ha with controlled release nitrogen accounting for 30% respectively for summer maize.The results showed that:compared with FH,only N1 increased the yield and net profit of winter wheat and summer maize for three consecutive years.For winter wheat,N1 increased significantly the yield by 4.0%,5.4% in 2017-2018 and 2019-2020,respectively,and still increased the yield by 1.6% even in 2018-2019 that the yields of other treatments were decreased.N1 also increased significantly summer maize's yield by 10.9%.In addition,after harvesting winter wheat and summer maize per year,amount of accumulation of inorganic N in 0-100 cm and 60-100 cm soil layer of N1 was significantly lower than that of FH, while the cumulative N use efficiency of N1 after 6 growing seasons of crop was increased by 11.3 percentage point.These results demonstrated that a mixture of CRU and urea (at a ratio of controlled release nitrogen accounting for 40% and 30% of the total nitrogen content for wheat and maize respectively)with a 10% reduction in N application rate compared to FH could be more beneficial to increase crop yield and nitrogen use efficiency, and reduce leaching of soil inorganic nitrogen in wheat-maize rotation system.

Key words: Wheat maize rotation, Nitrogen reduction, Controlled-released urea, Yield, Nitrogen use efficiency