Effects of controlled-release and stable urea application on soil nitrogen transport and yields of winter wheat and summer maize

The combined application of controlled-release and stable urea can enhance the efficiency of nitrogen management. In the present study, a combination of polyurethane-coated controlled-release urea and inhibitor-coated urea were used to study the effect of nitrogen transformation in winter wheat and summer maize. The results will provide new ideas and technical means for the development of high-efficiency fertilizer and limited non-point source pollution. The study included six treatments: no nitrogen application (control), traditional nitrogen application CV, 285 and 225 kg(N)·hm^-2 in wheat and maize, respectively, optimized nitrogen application OPT, 199.50 and 157.50 kg(N)·hm^-2 in wheat and maize, respectively, controlled-release urea + traditional urea application (CRF1, 40% and 30% controlled released nitrogen for wheat and maize, respectively), controlled-release urea + inhibitor-coated urea (CRF2, 30% and 20% controlled released nitrogen for wheat and maize, respectively), and controlled-release urea + inhibitor-coated urea (CRF3, 50% and 30% controlled released nitrogen for wheat and maize, respectively). CRF1, CRF2 and CRF3 were all the optimized nitrogen application, which significantly reduced cumulative ammonia volatilization during the summer maize and winter wheat seasons by 24.90%-57.00% and 10.20%-27.80%, respectively, compared with OPT treatment. At the same nitrogen application rate, the cumulative ammonia volatilization of CRF2 and CRF3 treatments were significantly lower than that of CRF1 treatment by 33.30%-42.80% and 12.20%-19.60% during the summer maize and winter wheat seasons, respectively. After fertilization, the rate of soil nitrate increase or decrease was greatest in CV treatment, followed by OPT, CRF1, CRF2, and CRF3 treatments. During the summer maize harvest period, the risk of residual nitrate leaching was highest in CV treatment, followed by OPT, CRF1, CRF2, and CRF3 treatments; whereas during the winter wheat season, leaching rate decreased as follows: CV, OPT, CRF2, CRF1, and CRF3. The yields of both winter wheat and summer maize under CRF1, CRF2, or CRF3 treatments were not significantly different from those of CV or OPT treatments. However, the net incomes of CRF2 and CRF3 treatments were 639 ￥·hm^-2 and 859 ￥·hm^-2 greater than that of CRF1 treatment during the summer maize season, whereas they were 1 196 ￥·hm^-2 less and 61 ￥·hm^-2 greater than that of CRF1 treatment during the winter wheat season. The favorable ratios of controlled-release nitrogen to stable nitrogen were 5:5 and 3:7 for winter wheat and summer maize, respectively, in the study area.