Switching to Switchgrass? Study Models Soil Impact of Biofuel Crops

by Kari Lydersen (Midwest Energy News) ... The Argonne modeling shows that when grassland, cropland and pasture in the Midwest are converted to corn for biofuels, the level of carbon sequestration in the soil stays roughly the same, with variation by individual counties.

Conversion of forest to biofuel crops usually has a negative effect on soil sequestration, including in the Midwest.

Switchgrass yields a neutral to positive change in soil sequestration in the Midwest, and there are strong positive changes in the Southeast when cropland and pasture is converted to switchgrass.

Poplar and willow yield largely neutral results, and the Midwest appears slightly more favorable than other regions for conversion to these biofuels, as far as carbon sequestration is concerned. Willow and poplar replacing existing forest may even mean positive changes in sequestration in the Midwest with the exception of Michigan and Wisconsin.

Miscanthus yields significant increases in carbon sequestration across the country; in the Midwest more so than other regions there could even be a positive change when forest is converted.

Researchers and growers in the Southeast have also shown much interest in miscanthus, though the Argonne modeling shows miscanthus’ soil sequestration capability actually may be lower in the Southeast than in the Midwest, relative to existing land use.

“For high-yielding crops like miscanthus – and there’s a similar pattern for biomass sorghum – are there depleted soils where planting these could both increase feedstock availability and also put carbon into the soil?” asked Dunn. “Where you can get multiple benefits out of doing one thing?”

Dunn noted that modeling the soil carbon question is especially valuable since there is very little observed field data on these issues, including for crops like miscanthus which are not widespread in the U.S.

When farmers leave crop residue on the field – a practice known as no-till – or reduce the amount of tilling they do, more carbon may be sequestered because the decaying organic matter adds to soil reserves, and soil disturbance which releases carbon is avoided. (However, the carbon benefits of no-till agriculture have also been questioned.)

The Argonne researchers noted that when corn is grown for biofuel, the stover left over from the stalk is also often harvested to be used as a biomass fuel source, while the corn kernels are used for ethanol production. Removing stover can reduce the sequestration of carbon in the soil, but it also increases the amount of biofuel that can be produced from the crop.

The researchers noted that in the Midwest not only are more crops grown but crops tend to have a higher yield per acre than in other areas of the country.

“Yield is one of the most important factors affecting soil carbon,” said Argonne post-doctoral researcher Zhangcai Qin. “If you have higher yield, you have more biomass, and with that you have more [organic matter] return to the soil. With corn, if you don’t remove the stover, it will eventually decompose and become soil carbon. So higher yield means higher soil carbon containment, which is a good thing.” READ MORE and MORE (Energy.AgWired.com)