Response of Sugarcane to Controlled-release Urea

This field experiment, initiated in 2013, continued to examine the effects of different rates and timing of controlled-release urea (CRU) on yield and economical returns of ratooned sugarcane in Wuming county of Guangxi. The experiment consists of nine treatments including: one check (omitting N), two regular urea (RU) treatments (100% N rate (670 kg N/ha), one treatment with two splits and another with three splits), three CRU treatments (70%, 80% and 100% N rates and two splits), and three treatments with different CRU and urea blends (60% CRU+40% urea, 80% CRU+20% urea, and 60% CRU+40% urea based on 80% of full N rate with two splits). Nitrogen fertilizers in all the CRU and blended treatments were applied basally at seeding (40%) and side-dressings (60%) at the seedling stage. For the two RU treatments, one applied N as is described above, while the other treatment split the N between seeding (30%), seedling (30%) and elongation (40%) stages. The P source was single superphosphate (18% P₂O₅) at 175 kg P₂O₅/ha, while K was applied as KCl (60% K₂O) at 880 kg K₂O/ha.

Except for much higher sugarcane yield obtained in the second ratoon season, the yield response to CRU treatments were similar to that observed in the previous year. The treatment of 60% CRU+40% urea achieved the highest cane yield (148 t/ha), followed by 80% CRU+20% urea, and 100% CRU. Cane yield decreased with lower N rates no matter if it was added as CRU alone or CRU blended with urea. The treatment of 70% CRU produced the lowest cane yield of 132 t/ha, indicating an appropriate N rate is essential to high cane yield. The urea treatment with three splits produced about 8.3 t/ha more cane yield than the urea treatment with two splits, showing the benefit of more N splits in this long growing season crop. Compared to the urea treatment with equal splits, the 100% CRU N rate increased cane yield by 9.0 t/ha (6.6%) and the 60% CRU+40% urea increased cane yield by 9.8 t/ha (7.2%). Economic returns followed the cane yield trends, indicating CRU can increase sugarcane yield and farm income.