Long‐Term Effects of Controlled‐Release Urea on Crop Yields and Soil Fertility under Wheat–Corn Double Cropping Systems

The long‐term effects of controlled‐release urea (CRU) on crop yields and soil properties were investigated in lysimeters under wheat and corn rotation system from 2009 to 2014 in northern China. The CRU included polymer‐coated urea (PCU), sulfur‐coated urea (SCU), and polymer coating of sulfur‐coated urea (PSCU) was applied at 147, 210 kg N ha −1 for wheat and 262.5, 375 kg N ha −1 for corn and the urea was applied at 210 kg N ha −1 for wheat and 375 kg N ha −1 for corn. Results showed that the N release characteristics of three kinds of CRU in field condition were all closely matched to the N requirement of crops. Consequently, the CRU treatments improved wheat and corn yields by 3.2 to 10.1% and 4.9 to 11.1%, increased apparent N use efficiency by 45.9 to 53.8% in wheat, and 36.2 to 45.4% in corn, respectively, compared with urea. Furthermore, the PSCU achieved the highest and the most stable crop yields among CRU. Even reducing CRU rate by 30% produced the same yields as with the 100% rate of urea. In addition, soil total N and organic matter contents in CRU were effectively increased in the topsoil of 0 to 20 cm after 5 yr. Therefore, long‐term application of CRU had great potential to increase wheat–corn yields, N use efficiency, reduce application frequency, improve soil fertility, decrease the leaching of soil NO 3 − –N and NH 4 + –N, and also relieve soil pH decreased. Core Ideas The long‐term effect of controlled‐release urea on crop yield and soil chemical properties was studied. The N release rates of controlled‐release urea were closely matched to the demand for N during the whole growth periods of crops. The wheat and corn yields were increased by 3.2 to 10.1% and 4.9 to 11.1% by controlled‐release urea fertilization, compared with urea treatment.