Effect of synergistic urea by nitrification inhibitor coated with resin on wheat growth and soil nitrogen supply

Combining nitrification inhibitor and urea can improve crop yield and nitrogen (N) use efficiency (NUE). However, the inhibitor easily gets inactivated in soil, making it difficult to achieve the desired effect. To develop a synergistic urea for increasing the inhibitor action time, soil N supply, and wheat growth, dicyandiamide (DCD) was coated after granulation with epoxy resin and then mixed with urea to develop new resin-coated DCD (RCD) synergistic urea. Scanning electron microscopy (SEM) and hydrostatic release tests were used to evaluate the membrane microstructure and the controlled-release performance of RCD. Five fertilization treatments were set up in the field: zero-N control (CK), urea (U), urea + common DCD particles (SUD1), urea + RCD (SUD2), and urea + both common DCD particles and RCD (3:7, weight/weight) (SUD3) to investigate the effects of the DCD synergistic urea on wheat growth, yield, and NUE and soil available N content. The SEM results showed that RCD had a complete coating, smooth surface, and small and rugged channels for DCD release in the profile. The hydrostatic release test at 25 °C showed that the release period of DCD was extended to ten days due to resin coating. In the three DCD synergistic urea treatments, only SUD3 resulted in a significant increase in wheat yield (18.47%) compared with U. The NUE in SUD3 was significantly higher than those in SUD2, U, and SUD1. The treatment SUD3 had higher soil available N content than the other treatments during the key wheat growth stages, while effectively reducing the risk of soil nitrate leaching during wheat maturity. In summary, SUD3, a mixture of urea, DCD particles, and RCD, was the best treatment for significantly increasing wheat growth, yield, and NUE and soil N supply.