Replacing common urea with controlled-release fertilizer at the recommended rate increases the yield and nitrogen fertilizer productivity of sorghum

Objectives We studied the availability and suitable rate of replacing common urea with controlled-release fertilizer in sorghum production, to propose a reasonable and efficient fertilization method.

Methods A field experiment was conducted in Yongchuan, Chongqing in 2021 and 2022, and the test sorghum varieties were Jinyunuo 3 and Jinnuoliang 1. Six treatments were set up, namely no nitrogen fertilizer (CK); ordinary urea at N rate 180 kg/hm² (U), ordinary urea at N rate of 20% less than U (U1, recommended N rate); controlled-release nitrogen fertilizer at N rate of 20% less (C1, recommended N rate), 30% less (C2), and 40% less (C3) than U. The sorghum dry matter accumulation (DMA) at anthesis and mature stages, yield and its components at mature stage were investigated.

Results The DMA of C1 and U1 at anthesis and mature stages were significantly higher than those of the other treatments, and the DMA of C1 was significantly higher than that of U1 at mature stage. The transport of leaf dry matter before anthesis of C1 treatment was significantly higher than that of U. The DAM after anthesis in C1 treatment was significantly higher than those in the other treatments, and those in U1 and C2 were significantly higher than that in U treatment as well. The contribution rates of DMA after anthesis to grain of C1 treatment were 11.54% and 12.41% higher than those of U for Jinyunuo 3 and Jinnuoliang 1, respectively. The yields of C1 treatment were the highest, 6611 kg/hm² for Jinyunuo 3 and 5690 kg/hm² for Jinnuoliang 1, which were significantly increased by 5.40%−18.66%, compared with the other nitrogen treatments. The yields of C2 and U1 treatments were second-highest, significantly higher than those of U and C3 treatments. All the treatments exhibited similar nitrogen physiological efficiency (NPE). The four N reduction treatments exhibited similar nitrogen agronomic efficiency (NAE), but distinct nitrogen partial factor productivity (NPFP). The NAE and NPFP of the four N reduction treatments were significantly higher than those of U treatment. The NPFP of the three controlled-release N treatments were significantly higher than that of U1 treatment. Compared with U treatment, C1 treatment significantly increased NAE, NPFP and NUE by 58.54%, 39.61% and 59.28% for Jinyunuo 3, and by 80.97%, 48.30% and 63.08% for Jinnuoliang 1. The NPFP and NUE of C1 treatment were 5.38% and 22.19% higher than those of U1 treatment for Jinyunuo 3, and 5.82% and 4.42% for Jinnuoliang 1.

Conclusions At the recommended N application rate, replacing common urea with controlled-release fertilizer could increase the dry matter accumulation at anthesis and mature stages, promote the transport of leaf dry matter before anthesis, enhance the dry matter accumulation after anthesis and its contribution to grain, thereby improve sorghum yield and nitrogen use efficiency significantly. Therefore, replacing common urea with controlled-release fertilizer at the recommended rate could be recommended as an efficient nitrogen fertilization method for sorghum production in southwest China.