Potential Losses of Macro and Micro Nutrients by Removal of Sugarcane Post-Harvest Crop Residue.

Green-cane harvest of sugarcane (Saccharum spp.) deposits large amounts of leaf residue onto the soil. Decomposition of crop residue recycles nutrients into the soil and maintains soil health. However, with the establishment of the bioenergy industry, crop residues may be harvested as feedstock for second generation biofuels. Sustainable agriculture, whether for sugar or bioenergy, must consider nutrient losses associated with removal of post-harvest residue. The objective of this study was to measure macro (N, P, K, Ca, S, Mg) and micro (Fe, Mn, Zn, Cu, B) nutrients in leaf material of three commercial sugarcane varieties throughout the sugarcane harvest season in south Louisiana (Sept. through Dec). Varieties HoCP 96-540, L 99-226, and L 99-233 were sampled at two-week intervals; both green and brown leaves were analyzed for total nutrient content using nitric acid/hydrogen peroxide digest and inductively coupled plasma spectroscopy. Nutrient concentrations were converted to an area basis using dry biomass per square meter data collected from across the Louisiana sugarcane growing region in 2009 (n=63). The mean post-harvest crop residue (± standard deviation) was 5.5 ± 2.2 Mg dry biomass ha^-1. Across varieties and date of harvest the amounts of total N, P, K, S, Ca, and Mg removed were 37, 4.1, 39, 4.6, 22, and 7.6 kg ha^-1, respectively, if one assumes complete removal via harvesting. Nitrogen concentration increased from 0.45% to 0.84% over time. Total B, Fe, Mn, Zn, and Cu removed was 44, 1700, 410, 23, and 72 g ha^-1, respectively. Using 2009 fertilizer economic data the value of the N, P, and K in 5.5 Mg residue would vary from $98 to $140 ha^-1 depending on the harvest date. Sugarcane crop residue represents a viable bioenergy feedstock. However, soil quality will likely be negatively impacted by its complete removal, and additional nutrients may be required to sustain yields. Feedstock value must surpass nutrient value (fertilizer equivalent) for harvest to be economically sustainable.