Effects of coated nitrogen fertilizer under one-time reduced application on yield and nitrogen use efficiency of winter wheat

Objectives Polymer-coated nitrogen fertilizer is the base to realize one-off fertilization of crop. We studied the availability of polymer-coated nitrogen fertilizer products when completely basal applied on winter wheat in Shandong Province.

Methods A field experiment was conducted from 2018 to 2021 in Huantai, Shandong Province, with two N rates for conventional rate of 225 kg/hm² (level 1) and a rate of 30% less (level 2). Four fertilizer products were tested, including common urea (BBF), polymer coated urea (PF), water-based polymer coated urea (WF) and mixture of PF and WF (MF), and no nitrogen fertilization was used as the control. The N release characteristics of PF and WF were tested in static water (25℃) and field. Wheat N uptake and yield were investigated, and the economic benefits were calculated. The soil N and organic matter contents were analyzed.

Results In static water, the N release period of PF was up to 119 days, while WF cumulatively released up to 84.7% within 14 days (25℃). Under field condition, the N release period of PF and WF lasted 210 days and 180 days, respectively, the release rate was in ‘S’ shape. Compared with conventional N application rate, reduction of 30% N input increased winter wheat N use efficiency and the agronomic efficiency and partial factor productivity of N significantly. At wheat seedling stage, BBF treatment had the highest soil \rmNO_3^- -N and \rmNH_4^+ -N contents, however, from the jointing stage, PF elicited the highest soil \rmNO_3^- -N and \rmNH_4^+ -N contents, which were significantly higher than BBF did. Under 30% less N input, controlled release fertilizers maintained relatively stable inorganic nitrogen contents in topsoil, and lower inorganic N contents below 20 cm depth of soil. Compared with BBF1 (N 225 kg/hm²), PF1 (N 157.5 kg/hm²), WF1, and MF1 increased winter wheat yield by 8.03%, 6.73% and 2.79%, and enhanced economic benefits by 18.55%, 15.92% and 7.06%, respectively; PF2, WF2, and MF2 had similar winter wheat yield, but significantly increased the economic benefits by 9.06%, 3.31%, and 6.86%, respectively.

Conclusions Under the condition of reducing the conventional nitrogen input by 30%, one-time application of both polymer coated (PF) and water-based polymer coated urea (WF), as well as their mixture maintained a high soil inorganic content throughout the wheat growth period; and further elicited wheat yield equivalent to the conventional urea application rate. The reduction of nitrogen fertilizer input and the application of coated nitrogen fertilizer greatly improved nitrogen use efficiency, nitrogen agronomic efficiency, and nitrogen partial factor productivity. Application of coated nitrogen fertilizer increased wheat yield, one-time fertilization reduced labor cost and increased the economic benefits of wheat production.