Sweet Sorghum for Biofuel Is an Alternative to Conventional Cotton-Peanut Rotation in the Southeastern U.S.

Sweet sorghum (Sorghum bicolor L. Moench) has high biomass productivity, and high tolerance to environmental stress conditions. Sorghum has gained interest as bioenergy crop because of its ability to attain high yields under water deficit, water logging, and low input requirements. However, in order to grow sweet sorghum for bioenergy production, current cropping systems will have to be modified or even completely replaced. There is a gap in our knowledge about associated impacts on biomass production and water dynamics when land-use changes from conventional cotton (Gossypium hirsutum L.)-peanut (Arachis hypogaea L.) rotation to sweet sorghum in the southeastern U.S. Cotton-peanut cropping systems are extensively grown in this area of the country and could potentially be substituted by sweet sorghum for biofuel purposes. We conducted a 3-year (2013-2015) field study to evaluate the effects of converting a conventionally grown cotton-peanut rotation to sorghum on biomass production and water dynamics. Furthermore, we evaluated the effects of land-applying two byproducts of the bioenergy industry namely biochar and vinasse as soil amendments to sorghum as alternative nutrient sources. We measured total dry matter production, soil moisture dynamics and drainage of a conventional cotton-peanut rotation compared to sorghum. Peanut dry matter was 70% lower compared to all other treatments in 2013. In 2014, excessive wet conditions during establishment period and sugarcane aphid damage during the summer severely reduced sorghum yield and cotton and peanut yielded 20 and 4 Mg dry matter ha-1 more than all sorghum treatments. Similar dry matter accumulation was achieved in the third year among crop species. Sorghum treated with biochar maintained on average 27% greater soil moisture content in the 0-10 cm soil layer during the study. Similar cumulative drainage was measured for all crop species evaluated. Under rainfed conditions, sorghum does not appear to significantly increase dry matter productivity compared to the total biomass production of conventionally grown peanut and cotton, but production cost is considerably lower. Additionally, biochar can improve soil moisture content at shallow soil layers where sorghum roots could benefit.