Tech Tuesday

Biomass Energy Sources Not Simple Crops

Switchgrass as a crop? Might not be so easy as many may think.

During my trip to the combined meeting of the American Society of Agronomy, the Crop Science Society of America and the Soil Science Society of America I spent time looking ad dozens of poster presentations. They covered a vast range of scientific inquiry, but one popular area revolved around biomass, or cellulosic, crops.

Switchgrass, miscanthus and other grassy crop types are getting a much deeper review in academia as researchers look at these crops can be commercialized. From exploring their life-cycles to better understanding their pests - there's a lot to learn.

While switchgrass, for example, is the apple in the eye of many cellulosic advocates, it's also a tough crop to establish. While work is being explore regarding nurse crops to get the switchgrass going, it's something to consider. Once established, the crop has a solid multi-year productive life providing plenty of material for a biomass energy plant.

A key question being explored is the nitrogen needs for those grassy crops. Any farmer knows that nitrogen and grass crops are a potent combination for high-output. Switchgrass is no different, but the key is to balance that N rate with the amount even a lush healthy crop would need. Researchers across the country are looking at N needs for the crop - and they range from 60 to 100 pounds per acre annually. However, that rate could be cut as more information becomes available about application timing.

Now comes word that there's at least one switchgrass pest we need to be aware of, which wouldn't surprise farmers - every crop has its pests. South Dakota State University scientists and colleagues, are working on adding knowledge about a "rediscovered" insect that thrives in switchgrass.

In an article published in the journal Zootaxa, the researchers described the immature stages of the insect species Blastobasis repartella. The scientists are already calling it the "switchgrass moth" and it bear studying.

This is the first important study of the moth since two male specimens of the adult moth were collected in Denver, Colo., in 1910. And what they've learned is that the moth could become one of the first pests of a new biobased economy. How potent is the pest?

In May 2004, at the Dakota Lakes Research Farm, Arvid Boe - a forage and biomass grass breeder - along with grad student DoKyoung Lee - estimated that up to 40% of new tillers of a few scattered plants of switchgrass was lost to the caterpillar. But many other plants were unaffected, so the total lost was estimated at less than 10%.

When first discovered by SDSU researchers they didn't recognize the pest, but being found in the biomass crop it gained the switchgrass moth moniker. No one knew what it was until they reached a research associate at the department of entomology at the Smithsonian Institution. A specialist in small moths, D.C. Adamski, identified the insect and informed SDSU researchers it has been identified in 1910, but little was known about the critter.

Interestingly, the pest may not be rare, but rather basically ignored in the entomology community. The moth appears to feed only on switchgrass and since the plant has - so far - been unimportant to humans the pest wasn't a worry.

This is a great example of how an insignificant pest can become an issue as a native plant is elevated to crop status. Asks Paul Johnson, curator of SDSU's Severin-McDaniel Insect Research Collection: "Part of the question from a biodiversity perspective is, how thoroughly do we know the insects of native prairie plants?"

He adds that converting native plants to crops may mean bringing along potential new pests and diseases to deal with. Encouraging large tracts of switchgrass as a crop could give those insects a signal to thrive. Says Johnson: "When you start encouraging large monocultures, it's like there's a Thanksgiving feast laid out for them."

One issue I've always questioned when switchgrass and other native-plant crops have been suggested is the idea that they might be "lower maintenance" than today's traditional crops. If the switchgrass moth turns out to be an economic pest; and if the crop has a disease complex; and it needs nitrogen, then frankly it'll take the same management as any other crop farmers raise.

The only great news about that is that American farmers already know how to keep weeds, insects and diseases under control to raise an economically viable crop. But for those saying these crops will be low-pest or low-maintenance? Well, nature may have a different idea. More work is, of course, required on this issue.

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