Nitrogen Supply and Harvest Dates Effects on Nutrient Removal and Biomass Chemical Composition of Energy Cane.

Consumption of whole-plant (stalk and leaves) cane for the production of lignocellulosic-based ethanol can potentially reduce soil moisture, organic matter and increase nutrient loss affecting sustainability of crop production. A field experiment was initiated in 2012 at LSU AgCenter Sugar Research Station in St. Gabriel, Louisiana to evaluate the fiber composition and amount of plant nutrients removed by energy cane applied with different nitrogen (N) rate and harvested at different dates. The experiment with a 2x4 factorial treatment structure was arranged in split plot in a randomized block design with four replications. The treatments included two energy cane varieties (Ho 02-113 and US 72-114) and four N rates (0, 56, 112, and 224 kg N ha^-1). Fifteen stalks were collected once a month beginning two months prior to the harvest date and were separated (into leaves and stalks) and analyzed for fiber and elemental composition using ANKOM²⁰⁰⁰ and Inductively Coupled Plasma - Optical Emission spectrometry, respectively. Nutrient uptake and biomass composition of energy cane were significantly affected by N application and harvest dates for both varieties (Ho 02-113 and US 72-114). All macronutrients uptake increased with N application but decreased at scheduled harvest. Cane leaves removed as much as 437 kg N ha^-1, 8.7 kg Ca ha^-1, and 2.5 kg Mg ha^-1. For both varieties, N fertilization resulted in an average of 35 and 24 Mt ha^-1 yield increase (P<0.05) for stalk and leaves, respectively. The negative effect of N on cellulose and hemicellulose was only observed on variety Ho 02-113 harvested two-months earlier than the scheduled harvesting. These preliminary results indicate that N fertilization increased energy cane yield as well as nutrient removal rate. The long-term effect of continuous farming coupled with complete removal of biomass from the field potentially includes decline in soil quality and productivity.