Effects of Nitrogen Fertilizer Source on Soil Inorganic N Content, Sugarcane Yield and Quality Parameters.

Optimizing nutrients uptake and yield in sugarcane (Saccharum officinarum) production is very important for the profitability of the sugarcane crop in Louisiana. A field experiment was established in 2015 at LSU AgCenter Sugar Research Station in St. Gabriel, Louisiana to assess the effect of fertilizer source on soil inorganic N levels, sugarcane yield and quality parameters. The experiment was arranged in a randomized complete block design on a Sharkey clay soil and complete randomized design on a Commerce silt loam soil with four replications. Data were collected from control plot, and those treated with 45, 90 and 135 kg N ha^-1 using controlled release fertilizer (CRF 45% N) and urea ammonium nitrate (UAN, 32% N) solution as sources. Soil samples were collected every two weeks from each plot at two depths (0 -15 and 15 - 30 cm), dried and analyzed for inorganic N (ammonium-N and nitrate-N) content. At harvest, ten stalks were collected, shredded, and analyzed for quality parameters using SpectraCane NIR system. Plots were harvested with a combine chopper and weigh-wagon for cane tonnage. Nitrate- and ammonium-N contents were higher in plots treated with UAN than CRF in both soil types, achieving ammonium-N levels >20 mg kg^-1 (4-6 weeks from N application). At a rate of 90 kg N ha^-1, plots on Sharkey clay soil treated with CRF performed better than UAN-treated plots based on theoretical recoverable sugar (TRS) levels. At rates of 45 and 90 kg N ha^-1, yields were higher in CRF- than UAN-treated plots. For the Commerce silt loam, CRF at 135 kg N ha^-1 obtained the highest millable stalk. The results from this study demonstrate the potential of both CRF and UAN knife-in as source of N for sugarcane production in Louisiana.