Response of Sugarcane to Controlled-release Urea

Sugarcane is considered to be an ideal crop to use controlled-release urea (CRU) because of its long growing season, high biomass production, and dense population that makes it difficult to fertilize, especially at mid to late growth stages. A field experiment tested different fertilization rates and timings of CRU application on sugarcane yields in Guangxi, the number one sugarcane-producing province in China. The experiment consisted of nine treatments including one check (CK, omitting N), two urea treatments (100% N rate (670 kg N/ha) applied in two splits and another in three splits), three CRU treatments (70, 80 and 100% N rates all applied in two splits), two treatments with different CRU and urea blends (CRU 60% + urea 40% and CRU 80%+urea 20%) applied in two splits, and one 80% N rate with CRU 60%+RU 40% blends. Except the CK and one urea treatment, N fertilizers in the other eight treatments were applied as basal at seeding and side-dressings at seedling stage in proportions of 40:60. In one of the 100% urea treatments, N was used at seeding, seedling and elongation stages in proportions of 30:30:40. Phosphate was applied as SSP (18% P₂O₅) at 175 kg P₂O₅/ha and K as KCl (60% K₂O) at 880 kg K₂O/ha.

Results showed that the CRU 60% + urea 40% treatment produced the highest cane yield (118 t/ha), followed by CRU 80% + urea 20%, and 100% CRU treatments. The cane yield decreased with a decrease in N rate, regardless of whether N was applied using CRU or urea. The lowest cane yield was obtained in 70% N rate (CRU), indicating an adequate N supply is essential to guarantee high cane yield. The urea treatment with three splits produced about 3 t/ha more cane yield than the two-split urea treatment, indicating the benefit of more N splits in long growing-season crops like sugarcane. Compared with the urea treatment with equal splits, the CRU 100% N treatment increased cane yield by 8.8 t/ha (8.2%) and the CRU 60% + urea 40% treatment increased cane yield by 10.7 t/ha (10%). Preliminary results have confirmed that the N rate being used in sugarcane production is appropriate and CRU performs better than urea for sugarcane fertilization.