Controlled-release urea improved rice yields by providing nitrogen in synchrony with the nitrogen requirements of...

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.

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 (NH₄ ⁺ -N), nitrate-nitrogen (NO₃ ^- -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 (Ca²⁺ ) and the cation exchange capacity increased in response to CRU.

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.