Sweet sorghum studies yield notable results

By Anna Austin
Researchers in Maryland studied the effects of delaying the harvesting of sweet sorghum cane by one month and found it was beneficial in cooler climates. The group is halfway through an additional project to evaluate long-term storage of sweet sorghum, results of which may help pave the way for an ethanol plant to be built in Maryland.

Last fall, Jeffrey Brenner of Solar Fruits Biofuels and researchers from Salisbury University, the University of Maryland at College Park, the Lower Eastern Shore Research & Education Center and local farmers collaborated to perform field trials to determine the effects of delaying the harvest of sweet sorghum cane by one month in cooler climates.

In preparation for the study, eight different varieties of sweet sorghum were established on one acre on a farm in Wicomico County in southeastern Maryland. "We did a comparison of an early harvest in September, and then a month-late harvest," Brenner said. "We did that because sweet sorghum is mostly grown in tropical areas where it can be harvested multiple times per year. But here (in the Northeast) and in parts of the country that see colder climates, you're not going to have more than one crop per year because of the short growing season."

Generally, the research indicated that when comparing the harvests, the delayed harvest resulted in a decrease in biomass, a decrease in juice volume and a decrease in sugar content, Brenner said. "When you looked at the total sugar and alcohol yield, there was a reduction of 14.5 percent from the first harvest to the second, by delaying it approximately one month," he said.

However, when harvested early the researchers found that the sweet sorghum was much too wet, containing a moisture level of about 29.5 percent, significantly above marketable grain levels. "By waiting a month and leaving it in the sun to dry, moisture levels came down to 18 percent, which is usable," Brenner said. "So by waiting a month you've lost a little of your theoretical alcohol yield, but you've gained 1 to two times (the amount) of grain per acre to be sold-so it's reasonable to delay it for a month."

The most recent study began in early November, and was performed mainly to investigate the "souring problem" of sweet sorghum, which happens when the crop is cut and left unprocessed for more than five days. "This occurs in tropical or hot climates-the same thing happens to sugarcane-where when you cut it, the sugar quickly disappears if you don't get it processed and take the juice out."

When sweet sorghum is crushed it becomes coated in bacteria, which access the juice inside of the plants and quickly divide, replicate and eat up the sugar. "So delaying your harvest will bring in a crop that doesn't contain a lot of sugar," Brenner said. The researchers aimed to test the five-day premise in cooler temperatures in which bacteria don't effectively grow.

The researchers also wrapped 100-pound sweet sorghum bales in plastic, and plan to leave them for six months to compare with unwrapped bales. After three months, results indicate that there is no significant loss of sugar or juice in the unwrapped bales compared with the wrapped bales. "This indicates that if you are up north, you may be able to plant more than your capacity, cut it and stockpile it like lumber, instead of using it all up right away," Brenner said. "In places such as Louisiana and Florida they can't do this, but they can plant three or four crops a year and harvest year-round."

Overall, the group believes that if the remaining three months of data is consistent with the first three months, stockpiling of long cane sweet sorghum could extend the operation of an ethanol plant in the northern climates beyond four months, which is what is currently thought possible with one crop per year.

Next year, the group will likely compare storing long cane sweet sorghum in billets (small chunks), different ways of making silage and temperature effects, Brenner said.