Green-Cane Harvest of Sugarcane Effects On Biomass and Energy Yields and Nutrient Removal.

Sugarcane yields in Louisiana approach 40 dry Mg ha^-1, making it an attractive biofuel feedstock as well as a profitable sugar crop. Existing technology used in green-cane harvesting can be controlled to allow chopper harvester extractor fans to remove variable amounts of extraneous leaf material from the cane stalk and deposit it on the soil surface during harvest. The objectives were to (1) evaluate biomass and energy yields of selected sugarcanes, (2) estimate residue nutrient losses, and (3) evaluate logistics of harvesting at different extractor fan speed settings simulating sugar or biomass harvest. A commercial sugarcane cultivar HoCP 96-540 and a high-fiber “energy” clone L 79-1002 were planted in 2009 and the plant cane was harvested in Nov. 2010. Three fan speeds (off – biomass harvest; 375 rpm – mid range; and 750 rpm – optimal for sugar harvest) were used. L 79-1002 (39 dry Mg ha^-1) produced more biomass than HoCP 96-540 (32 dry Mg ha^-1). The increased biomass yield of L 79-1002 equals to an increase of 77 GJ of energy ha^-1. Slowing or stopping extractor fans increased dry biomass yield by 8-12 Mg ha^-1. However, turning off extractor fans increased nutrient removal from field by 9, 2, and 13 kg of N, P₂O₅, and K₂O ha^-1, respectively, when compared to the 750 rpm fan speed. The biomass harvest strategy with the harvester's extractor fans turned off – designed to remove as much total biomass as possible – increased the number of cane wagon loads by a factor of 1.6, due to lower density of crop residue. This will extrapolate to increased haul loads to a potential biofuel processing mill and reduce the economic efficiency of the production supply chain. Adoption of biomass harvest strategy using existing sugarcane harvest technology produced dry feedstock yields of 39 Mg ha^-1, but a reduced yield may be more sustainable when nutrient losses associated with residue removal are taken into account.