Double-Cropping Sorghum for Biomass

Double-cropping systems have been suggested as a way to increase annual dry matter production per hectare, while simultaneously delivering environmental benefits. Past research seems to indicate that there is a genotypic effect for the suitability of a crop for use within double-cropping systems; however, despite sorghum’s diverse genetic background, there has not been a great deal of work done to explore this response for this crop.

A team of researchers from Iowa State University grew twelve sorghum varieties as sole crops and within a double-cropping system with winter triticale in central and northern Iowa. Theor results showed that although the single-cropping system produced slightly higher biomass yields, there were no significant differences in total production between the two systems for several of the sorghum varieties.

These varieties were characterized as earlier maturing ones that had nearly maximized dry matter production at the time of harvest for the double-cropping system, and thus, any potential loss in sorghum yield was supplemented by the biomass production from the triticale crop. However when the chemical composition of the crops was considered, the theoretical ethanol yield of the single-cropping system was greater than the double-cropping system for all sorghum varieties. Although triticale was capable of offsetting any potential loss in dry matter, as an ethanol feedstock it was inferior to sorghum.

Although capable of producing equivalent dry matter yields, the use of the double-cropping systems for ethanol production may be limited due to differences in the production and chemical composition of the two crops.

The authors say that from a production standpoint, growing sorghum as a sole crop is more efficient for ethanol production, however, it remains to be seen whether the favorable long-term environmental benefits, such as reduced erosion potential, of the double-cropping systems merits the reduced total biomass production.

Within the single-cropping system, the top-yielding sorghums were either photoperiod sensitive or late maturing varieties. This was in contrast to the double-cropping systems, in which early maturing varieties had the highest sorghum yields. This seems to indicate that the suitability of sorghum for double-cropping depends largely on the inherent genetics of the variety and that selection for use within double-cropping systems should be based on the cultivar’s ability to maximize dry matter production earlier in the growing season.

The authors recommend that further research on double-cropping systems for ethanol production should focus on efforts to maximize production of the sorghum crop, such as incorporating a winter annual that matures earlier in the season. This would allow planting of the sorghum closer to its optimal date and capitalize on its ability to produce greater and higher-quality biomass, and theoretical ethanol yield, over a greater portion of the growing season.
 

Information taken from:

Double-Cropping Sorghum for Biomass
Ben M. Goff,* Kenneth J. Moore, Steven L. Fales, and Emily A. Heaton
Published in Agron. J. 102:1586-1592 (2010)
Published online 13 Sep. 2010

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Abstract: https://www.agronomy.org/files/publications/agronomy-journal/abstracts/102-6/aj10-0209-abstract.pdf