Enhanced-Efficiency Urea Coated with Ground Phosphate Rock Powder, Inhibitor and Epoxy Resin: Preparation and Effects on Soil Nitrogen Supply Capacity, Wheat Yield and Nitrogen Use Efficiency

A develop a new environmentally friendly controlled-release urea to improve soil nitrogen supply capacity, wheat yield and nitrogen use efficiency, six coated urea were prepared in this study: resin-coated urea; phosphate rock powder-coated urea; phosphate rock powder and epoxy resin-coated urea; urease and nitrification inhibitors combined with epoxy resin-coated urea; urease and nitrification inhibitors combined with phosphate rock-coated urea; and urease and nitrification inhibitors combined with phosphate rock and epoxy resin-coated urea (RPHDU). Scanning electron microscopy and hydrostatic release tests were used to evaluate the microstructure and controlled-release properties of different urea. Using zero nitrogen treatment and conventional urea treatment as controls, six self-made coated urea were used for different fertilization treatments, with a total of eight treatments set up for ammonia volatilization test and field experiment to study the effects of different fertilization treatments on ammonia volatilization, soil nitrogen supply capacity, wheat yield, and nitrogen use efficiency. The results showed that the RPHDU coating had a complete and tight membrane shell. RPHDU had controlled-release periods for nitrogen, hydroquinone, and dicyandiamide (cumulative nutrient release > 80%) of 112, 56, and 28 days, respectively, effectively controlling the release of nutrients and inhibitors. The treatments of adding inhibitors delayed the ammonia volatilization peak and reduced the peak value, with the RPHDU treatment having the lowest cumulative ammonia volatilization. During the critical growth period of wheat, the soil available nitrogen content in the RPHDU treatment was higher than in other treatments, which brought soil nutrient supply closer to wheat demand. Moreover, the soil apparent nitrification rate was lower in the RPHDU treatment than in other treatments throughout the entire wheat growth cycle, reducing the risk of nitrate nitrogen leaching. The RPHDU treatment achieved the highest wheat yield and nitrogen use efficiency, which were significantly increased by 21 and 21%, respectively, compared to the U treatment. In summary, RPHDU could more effectively control nutrient release, improve soil nitrogen supply capacity, reduce soil nitrogen loss, and increase wheat yield and nitrogen use efficiency. The results of this study may provide a basis for the development of novel and environmentally friendly fertilizers.