Brown and green sugarcane leaves as potential biomass: How they deteriorate under dry and wet storage conditions

• The use of sugarcane leaves as a biomass feedstock has made information on their deterioration under wet and dry conditions more important.
• Worst deterioration occurred for both brown and green leaves when leaves were wet.
• Only prolonged deterioration of brown leaves caused a reduction of fiber biomass.
• Total microbe populations were highest on watered green leaves because of higher available nutrients.

The current trends to (1) investigate sugarcane leaves as a sustainable biomass feedstock for the production of biofuels and bioproducts and (2) delivery of more leaves to factories for processing with stalks, have made information on how it deteriorates on storage during dry and wet environmental conditions more important. Brown, dry (BL) and green leaves (GL) were stripped from hand-cut whole-stalks from Louisiana (LA) sugarcane variety LCP 85-384 in two consecutive years. In the first year, BL and GL were separately allowed to deteriorate in a simulated field canopy shade study. One set was watered across 14 days to simulate rain, and the other set was not watered. This 14 day period was repeated three times across the LA harvest season (October to December) to cover varying environmental conditions: 17–31 October (21 °C; 71% mean humidity), 15–29 November (22 °C; 71%), and 13–27 December (15.5 °C; 78%). In the second year, the simulated study was repeated but over a prolonged 28 day period (17 November–15 December) and fresh and deteriorated leaves were also collected from a grower's LCP 85-384 field and analyzed for comparison. Generally, the worst deterioration for both BL and GL occurred in the watered samples, and when the humidity was highest. On deterioration, more soluble impurities were extracted from GL than BL. Only prolonged deterioration of BL caused a reduction of fiber biomass, and the fiber content of GL usually increased on deterioration because of loss of moisture. The nutrient sucrose was often, but not always, preferentially utilized over glucose and fructose. Results from the grower's field were more extreme than from the simulated experiments. Leaf moisture was higher in the deteriorated than non-deteriorated field BL because its shredded state created more surface area to absorb water; this also allowed for more Leuconostoc mesenteroides bacteria to grow and form dextran and mannitol. Overall, the total microbe populations were highest on watered GL because of higher available nutrients.