Changes in Cane Leaf Nitrogen Content and Soil Inorganic Nitrogen As Affected By Fertilizer Application Timing and Soil Type.

Efficiency of nitrogen (N) fertilization in sugarcane (Saccharum officinarum) production can be affected by application timing and soil type. This study was conducted to determine the effect of fertilizer application timing and soil type on soil nitrate and ammonium along with leaf N content of sugarcane at different critical growth stages. Established in 2015 at two locations in St. Gabriel, LA, treatments were set in a randomized block design on a Sharkey clay soil and in a complete randomized design on a Commerce silt loam, using sugarcane variety L01-299. Granular (Agrocote Max®, 45%N) and solution (urea ammonium nitrate solution-UAN, 32%N) N sources were applied at rates of 45, 90 and 135 kg N ha^-1 and at two application timings (March and April). All these treatments including a control (0 Kg N ha^-1) were replicated four times. Every two weeks (following March fertilization) sixteen soil cores at depths 0-15 and 15-30 cm were taken from each plot. Beginning in April, eighteen leaf samples were taken from each plot. Soil and leaf samples were dried at 60^oC and processed. Ammonium and nitrate were extracted from the soil samples using the KCl extraction procedure and then measured using a flow injection analyzer. Total leaf N content was determined using a CN analyzer. Soil ammonium-N began to increase four weeks after the March fertilizer application and two weeks after the April application in both clayey and silt loam soil types. For March applications, soil ammonium-N reached higher levels in the clayey soil compared to silt loam. The various rates of fertilizer could also be distinguished for both times of application. In general, sugarcane fertilized with N in March showed higher leaf N content than those applied in April. Both fertilizer application timing and soil type influenced soil ammonium-N levels and sugarcane leaf N accumulation.