Biomass dilemma: Double crop or not?

IOWA STATE (US) — An experiment to test the benefits of double-cropping to grow more biomass for ethanol production yields mixed results.

Researchers planted triticale, a relative of wheat, in the fall and harvested it in the spring. Then they planted sorghum in early June and harvested it in mid-September.

Twelve different varieties of sorghum were tested with the triticale. Of those, four test plots produced as much biomass as a single crop of sorghum alone yielded in the same year. Details are reported in the Agronomy Journal.

“The sorghums planted with the single-cropping system were planted a little earlier and harvested later,” says Ben Goff, who conducted the researcher as a graduate student at Iowa State University.

The longer growing season for the single-cropping sorghum produced more biomass in eight of the 12 sorghum types. The other four types of sorghum were early maturing varieties, and they produced an equal amount of biomass as the single-crop sorghum. These yielded less ethanol than the single-crop sorghum.

While the research didn’t produce an increase in biomass, there are benefits to the double-cropping system, according to Goff.

“The winter crop reduces soil erosion,” says Goff. “And some studies have shown that having the crop in the field captures spring nitrogen early in the year so it doesn’t move through the soil profile.”

Sorghum and triticale were chosen as the crops to pair together for several reasons, according to Goff.

“Sorghum is a potential energy crop,” he says. “You can get a lot of biomass in a shorter growing season. Also, sorghum is more drought tolerant, and using a two-crop system may leave you with moisture limitations. Sorghum has many of the same farm practices as corn, so it would be a crop farmers would be comfortable with producing.”

Sorghums, especially sweet sorghums, have high concentration of soluble sugars which are readily fermentable for ethanol, according to Ken Moore, professor of agronomy.

Triticale is a good winter crop that produces much biomass during the winter, says Goff.

While the research didn’t net an increase in biomass, Goff doesn’t declare the idea a failure.

“This still has potential. If we can get an earlier maturing annual winter crop, I think we can get greater yields,” says Goff. “Basically, we are trying to utilize more of the sun’s energy to produce more biomass.”

Moore thinks that sorghum double-cropping may be environmentally beneficial in certain farmland. “Double-cropping may have some real benefits for land that should not be exposed to erosion in winter.”

The research was funded by the Iowa Energy Center.

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