Maize yield and economic return with controlled-release urea

Balancing fertilization of nitrogen, phosphorus, potassium and the use of controlled-release fertilizers are valuable practices for increasing yield and nutrient use efficiency. This 8-year field study was conducted using a mixture of controlled-release urea and soluble urea to evaluate maize yields, net returns and nutrient interactions in the North China Plain. The treatments included nitrogen application rates at 0, 150, 300 and 450 kg ha−1 using mixture; phosphorus application rates at 0, 16, 32 and 48 kg ha−1; and potassium application rates at 0, 125, 250 and 375 kg ha−1. The treatment using only soluble urea as the nitrogen source represented the standard farming practice in the region, with nitrogen, phosphorus and potassium being applied at 300, 16 and 250 kg ha−1, respectively. The results showed that the net return of the treatment with nitrogen, phosphorus and potassium being applied at 300, 16 and 250 kg ha−1, was increased by 14.8% over that of the farming practice treatment. Notably, controlled-release urea reduced the risks of decreased yields associated with price fluctuations. Multiple regression analysis results (R2 = 0.9726, P = 0.009) suggested that the coefficients of nitrogen × phosphorus, nitrogen × potassium were synergistic, while that of phosphorus × potassium was antagonistic. The interaction effects of the two factors decreased in the order nitrogen × potassium > nitrogen × phosphorus > phosphorus × potassium. The optimal maize yield was 9.2–9.3 t ha−1 at nitrogen, phosphorus and potassium application rates of 276–290, 27–29 and 210–226 kg ha−1, respectively. This study demonstrates that balanced fertilization based on controlled-release urea and soluble urea blend can improve maize yields and net returns.