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Do mixed wild grasses make the best biofuel?

Scientists at the University of Minnesota have found that native wild grasses, shrubs, and tree seedlings may provide more energy as a biofuel than crops such as corn, oil seeds, sugar cane, or switch grass. Native species also store more atmospheric carbon dioxide in soils and lead to less chemical pollution than crops cultivated for biofuels.

The researchers seeded 152 plots of land that were so sandy and nutrient-poor that farmers had abandoned them long ago. They planted from one to 16 species of grassland perennials on each plot. Most were grasses and shrubs. Some plots hosted a few oak seedlings. The land was unfertilized during the experiment, and the team watered the plots only at the outset.

The experiment ran from 1994 to 2005. In the final three years, researchers found that the greater the diversity of plants on a plot, the greater the energy content of the plant material. Computer simulations showed that, when used in synthetic gasoline or diesel fuel, these plants would produce 51 percent more energy per hectare from degraded land than corn does from fertile soils. Moreover, corn ethanol and soybean biodiesel are carbon-positive sources after taking into account the CO2 emitted in growing and burning them. The wild grasses so enriched the soils with carbon and required so little human attention that they were carbon-neutral – even after they were burned as an additive to coal or turned into ethanol and burned. The research appears in the current issue of the journal Science.

Mystery of the Martian crust

A team of scientists has found that the crust under Mars' northern lowlands is far older than many believed. That's an important clue for scientists trying to solve one of the planet's enduring mysteries: Why the stark difference in terrain between the northern and southern hemisphere?

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