Response of Sugarcane to Controlled-release Urea

Guangxi, the largest sugarcane-growing province in China, accounts for about 70% of the sugarcane production in the country. Sugarcane is a tropical and subtropical perennial crop with a long growing season of about 8 to 10 months. A high yielding crop of 50 to 60 t cane/ha requires a large quantity of fertilizer with multiple applications, especially for N. This project is examining the effects of fertilizer application timing of controlled-release urea (CRU) compared to regular urea (RU) on sugarcane yield. The trial consisted of nine N treatments, including zero N, 100% RU with three splits (one basal + two topdressings), 100% RU with two splits (one basal + one topdressing), 100% CRU with three splits (one basal + two topdressings), three reduced CRU rates (80%, 70% and 60%) with two splits, two combined treatments of 60% CRU+40% RU and 80% CRU+20% RU applied twice, one combined 60% CRU+40% RU providing a reduced total N rate (80%) applied twice. The 100% N treatment provided 330-150-375 kg N-P₂O₅-K₂O/ha. The CRU was a polymer-coated urea (42% N) from Agrium and the RU (46% N) was purchased from the local market. The basal fertilizers were incorporated into soil and the topdressings were side-banded between rows.

The treatment fertilizer source effects on sugarcane yield were highly significant. The 100% CRU and the two blended CRU+RU treatments surpassed the 100% RU treatments in both yields and sugar contents. However, cane yield differences among these three treatments with partial or full rates of CRU were not significant, implying blending CRU with RU can maintain cane yield levels with reduced fertilizer cost. Cane yields decreased with a lower CRU application rates. As expected, splitting applications of RU in three doses boosted cane yield more than with two applications. Sugar contents, sugar yields and economic returns were affected by different treatments in a similar manner.