Strategies for Increasing the Harvest Window of Sweet Sorghum in Arizona, Poster Board #108

As our dependence on fossil fuels is being weaned, domestic alternatives to petroleum are being investigated.  We have previously reported that sweet sorghum (Sorghum bicolor Moensch) can be grown in Arizona with reduced inputs and on marginal lands not otherwise suitable for food crops.  Current harvest times are determined by flowering; 30 days after half of the plants are flowering.  In previous studies, we collected single stalk samples over the entire growing season and hypothesized that some lines could be harvested earlier with the same sugar yield, thus reducing time and inputs, while adding the potential for a second crop.  In regions with longer growing seasons, such as Arizona, the capability to have multiple harvests or double crop sweet sorghum is important as it adds flexibility to management systems and extends the harvest season, as well as providing a more constant availability of feedstock for processing facilities.  Four varieties (Dale, M81E. 350FS, and Sugar T), with different days to maturity, were planted on May 26, 2011, and harvested at four dates (90, 120, 150, and 180 days after planting).  The harvested area was 3.05 m in the middle two rows of each plot, with three replications. Stalks were cut at 3 cm above the soil level and the field weight of the plots recorded.  A sub-sample of 15 cut plants was weighed, then stripped of leaves and panicles, and weighed again.  The 15 stripped stalks were run through a roller mill, and the juice collected and weighed. °Brix was recorded in the field, and juice samples transported on ice to the laboratory for sugar analysis using HPLC. The field biomass did not change significantly among any of the harvests or varieties.  There were significant interactions among varieties and harvest dates for juice weight; with juice weight highest for 350FS and Sugar T at all harvest dates, but not significantly higher than M81E at 120 and 180 days.  There was a significant increase in total sugar, with most varieties doubling between 90 and 120 days, but the differences between the last two harvests were not significant.  We have previously shown that biomass and total sugar are the best predictors of ethanol yield, so these data indicate that 350FS, M81E, and Sugar T can all be harvested at 150 days, 30 days earlier than predicted by plot flowering, and Dale harvested at 120 days after planting.