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

Abstract

Combining nitrification inhibitor (NI) and urea can improve crop yield and nitrogen use efficiency (NUE). However, the inhibitor easily gets inactivated in the soil, making it difficult to achieve the desired effect. To develop a synergistic urea for increasing the inhibitor action time, soil nitrogen supply and growth of wheat, dicyandiamide (DCD) was coated after granulation by epoxy resin, which was then mixed with urea to develop a 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 the RCD. Five treatments of different N fertilization were set up in the field: (i) the zero-N control (CK); (ii) urea (U); (iii) urea + 100% common DCD particles (SUD1); (iv) urea + 100% RCD (SUD2); (v) urea + both 30% common DCD particles and 70% RCD (SUD3) to investigate the effects of the synergistic urea on the growth, yield, and NUE of wheat and the available nitrogen content of soil. The SEM results showed that the RCD had a complete coating, smooth surface, and had small 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 10 days due to the presence of resin coating. Compared with the U treatment, the wheat yields of SUD3 treatment significantly increased by 18.47% in three treatments with DCD. The NUE in the SUD3 treatment was 18.48% significantly higher than that in the U treatment. SUD3 had higher soil available nitrogen concentration than the other treatments during the wheat key growth period while effectively reducing the risk of soil nitrate leaching during wheat maturity. In summary, SUD3 of urea, DCD and RCD mixture was the best treatment for significantly increasing the growth, yield, and NUE of wheat and soil nitrogen supply.