Diverse native grassess edge out crops as biofuel

Mixtures of plants native to prairies can give a better energy return as biofuel than corn and soybeans do, a newstudy finds. Biofuel production from grassland plants would also result in lower emissions of carbon dioxide and reduced pollution from agricultural chemicals.

Corn-grain ethanol and soybean biodiesel are starting to replace some gasoline and petrodiesel (SN: 7/15/06, p. 36: http://www.sciencenews.org/articles/20060715/fob4.asp). However, corn and soy crops need large amounts of pesticides, water, and fertilizers.

Ecologist David Tilman of the University of Minnesota in St. Paul and his colleagues determined the resources required for and energy gained from biofuels made from perennial grassland plants. These species wouldn't require regular herbicide treatments, irrigation, or fertilization and could be grown on agriculturally abandoned land. Grassland plants aren't yet used in biofuels.

In 1994, the researchers planted 152 plots of agriculturally degraded land with different numbers of perennial grassland species, such as legumes, grasses, and herbs. They monitored and sampled the plots from 1996 to 2005.

The researchers found that the most diverse plots — those with 16 different species — were also the most productive,with the potential to generate more than three times as much energy as plots that bore only one species. The prairie-grass mixtures would give a net energy return that's more than 17 times that of corn-grain ethanol, Tilman says.

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