Effects of modified urea ammonium nitrate solution topdressing on ammonia volatilization and leaching

In this study, with urea ammonium nitrate solution as raw material, NBPT (n-butyl thiophosphoric triamide) and DMPP (3, 4-dimethylpyrazole phosphate) were used as inhibitors, and polyurethane as a protective agent to develop two modified urea ammonium nitrate solutions (YUL1 and YUL2). And their effects on ammonia volatilization and leaching loss in summer maize in the North China Plain were studied. In the field experiment, six treatments were set up: 1) no urea application (CK), 2) farmers' traditional urea application (CN), 3) optimized urea application (CNU), 4) application of optimized urea ammonium nitrate solution (UAN), 5) and 6) optimized modified urea ammonium nitrate solution 1 (YUL1) and 2 (YUL2) application. The effects of nitrogen regulation characteristics were systematically evaluated. The properties of the products were analyzed by scanning electron microscope (SEM) and energy disperse spectroscopy (EDS). The in-situ continuous dynamic observation of ammonia volatilization and nitrogen transformation was carried out within 15 days after nitrogen application (which occurred at bell mouth stage of summer maize); the yield and economic benefits were measured and calculated at the maturity stage of maize. The results showed that the modified urea ammonium nitrate solution was clear and free of impurities, the film surface was smooth and dense after casting, and the inhibitors were evenly distributed on the film surface. The content of phosphorus and sulfur on the film surface was increased by energy spectrum test, which proved that the composite inhibitors and urea ammonium nitrate solution achieved effective fusion. Under the same optimized nitrogen application rate, compared with CNU, the total amount of ammonia volatilization of YUL1 decreased significantly by 19.3% and YUL2 increased by 9.6%. Compared with UAN, YUL1 and YUL2 decreased the total amount of ammonia volatilization significantly by 57.3% and 42.0%, respectively. Compared with other nitrogen application treatments, the soil layer of 0-20 cm in the middle and late period of summer maize growth of YUL1 and YUL2 treatments still maintained relatively higher nitrogen contents. After harvest, the soil nitrate nitrogen contents of YUL1 and YUL2 were 46.0% and 43.4%, respectively, higher than that of CNU, and 45.6% and 44.7% higher than that of UAN in the 0-20 cm soil layer; in the soil layer of 180-200 cm, they were significantly lower than those of other treatments. With regard to ensuring the yield and net income of summer maize, the modified urea ammonium nitrate solution significantly reduced ammonia volatilization and leaching loss of nitrogen.