Controlled‐release urea improved rice yields by providing nitrogen in synchrony with the nitrogen requirements of plants

Abstract BACKGROUND Excessive application of nitrogen (N) fertilizer and low nitrogen‐use efficiency (NUE) are prevalent problems in rice production. Controlled‐release urea (CRU) is widely adopted to increase rice yields, but the synchronicity of N release from CRU with uptake of N by plants has rarely been studied. A 2‐year field experiment involving CRU and urea applications at three different N rates (240, 192 and 144 kg N ha −1 , equal to 100%, 80% and 60% of the recommended rate, respectively) was performed to compare their effects on N uptake, soil N content and rice yields. RESULTS The successive release curves of CRU in the soil matched the corresponding N uptake curves of rice plants, and significant linear correlations were observed. Grain yield and N uptake under the CRU treatment increased by 5.25–7.88% and 7.13–17.94% than urea treatments, at the same N rate, and no obvious difference was found between CRU60% and Urea100%. CRU80% and CRU60% presented the highest NUE. The contents of ammonium‐nitrogen (NH 4 + ‐N), nitrate‐nitrogen (NO 3 ‐ ‐N), and total N and the chlorophyll relative value – SPAD (Soil Plant Analysis Development) values – of the leaves under the CRU treatments were significantly higher than those under the urea treatments from heading to harvest. The contents of exchangeable sodium ion (Na + ) and calcium ion (Ca 2+ ) and the cation exchange capacity increased in response to CRU. CONCLUSION CRU increased rice yields by providing N strongly in synchrony with the N requirements of the plants, and applying CRU at 192 kg N ha −1 was an effective strategy to conserve N fertilizer, increase soil N contents and enhance NUE. © 2021 Society of Chemical Industry