Controlled Release Nitrogen Fertilizer and Application Timing: Soil N, Leaf N, and Yield Response in Sugarcane.

Controlled release fertilizers (CRF) have recently entered the agronomic market, altering conventional nitrogen (N) rate recommendations. Sugarcane (Saccharum officinarum), N status along with millable stalk and sugar yield can be influenced by soil texture and time of N fertilizer application. Intentions of this study was to evaluate effects of CRF applied at different times on leaf N content, soil N, and yield of sugarcane grown on two soil types. Sugarcane variety L01-299 was used in St. Gabriel, LA. Two sites were selected; set in a randomized block design and a complete block design for Sharkey clay and Commerce silt loam (sl) soil. Two N fertilizer sources, CRF (45%N) and UAN (urea ammonium nitrate, 32%N) were applied in March and April at rates of 0, 45, 90 and 135 kg ha^-1. All treatments were replicated four times. Eighteen leaf samples per plot were taken every two weeks after fertilization, dried at 60^oC, processed and analyzed for N using a CN analyzer. Soil ammonium and nitrate were analyzed using flow injection analysis. Millable stalk yield was determined with a combine harvester and weigh wagon whereas theoretical recoverable sugar (TRS) and sucrose content were measured in shredded stalk using near infrared spectroscopy. Less effect of application timing on leaf N content appeared in Sharkey clay. Plots applied with CRF had lower soil inorganic N levels than UAN during the early growth stages of cane. Cane tonnage and sugar yield response to fertilizer rate was more evident in Commerce sl than in Sharkey clay soil. In addition, fertilizer applications in April resulted in higher cane tonnage and sugar yield in Sharkey clay. Sucrose and TRS values were higher in UAN applied sugarcane. The N source and application timing should be tailored with soil type to optimize yield and N use efficiency in sugarcane production.