Ethanol Yield and Nutrient Removal for Biofuels Crops.

Increasing demand for biofuels sources has motivated the need for knowledge about diverse crops or rotated crops for ethanol yield and nutrient removal, a very important factor that must be considered in bioenergy. This study was conducted to determine dry matter production (grain, residue, total biomass) and estimated ethanol yields and nutrient balance (N, P, K) of annual and perennial crop in west Uruguay for six years (2008-2014). Sweet sorghum (Sorghum bicolour) grown continuously; corn (Zea mays L.) rotated with wheat (Triticum aestivum) and grain sorghum (Sorghum bicolour) with two residue harvest scenarios removed (without or low cut) and perennial grass as switchgrass (Panicum virgatum L.) were evaluated. The total highest ethanol in these six years evaluated were achieved with switchgrass (27.270 L ha^-1) followed by rotated corn-wheat-sorghum with residue removed (21.150 L ha^-1). The lowest treatment was with sweet sorghum with only 10.100 L ha^-1. Total N-P removal rates were greatest for grain crops rotated (578 Kg N ha^-1 and 138 Kg P ha^-1 and 571 Kg N ha^-1 and 155 Kg P ha^-1 without or with straw removal treatments, respectively). However, the total K removal rates were highest for switchgrass and continuous sweet sorghum (419 and 349 Kg K ha^-1, respectively). These results indicate that perennial grasses as switchgrass can produce greater total biomass and then greatest estimated ethanol yields for renewable fuel production. However, high biomass removal could increase extra fertilizer inputs to maintain soil productivity.