(NaturalNews) Biofuel produced from a fast-growing variety of grass can produce 540 percent more energy than is used during its manufacture, according to a study conducted by researchers from the U.S. Department of Agriculture (USDA) and published in theResearchers grew switchgrass on 10 different farms, ranging between three and nine hectares in size, for five years. They calculated the energy used to produce the fertilizers, herbicides, diesel and seeds used in the switchgrass production. Because no large-scale biorefineries currently exist, the researchers used estimates to calculate how much biofuel could be produced from the switchgrass farms' output.In contrast to an earlier study, which found a net energy gain of 343 percent, the researchers found a 540 percent energy gain from switchgrass.The researchers did not include in their calculations how much energy used to ship the switchgrass to a refinery. In order to keep these costs low and the energy output high, they recommended that biorefineries be constructed near the fields on which switchgrass is grown."A biorefinery will have a feedstock supply radius of about 25 to 50 miles, so the feedstock of any biorefinery needs to be localized," said co-author Ken Vogel, of the USDA's Agriculture Research Service.The United Nations and other organizations have criticized the biofuels industry for taking arable land out of food production and using it to produce fuel instead. According to Vogel, one of the advantages of switchgrass is that it can be grown on marginal cropland."The intent is to have energy crops being grown on marginal cropland, so it would not be in competition with food crops on our best land," he said.Another advantage switchgrass has over other oil crops, such as corn, is that the entire plant and not just a seed can be used to produce ethanol, leading to much higher yields per ton.