Effect of Sorghum Biofuel Production Systems On Soil Characteristics in Souteastern U.S.

According Energy Policy Act of 2005, the U.S. must to produce 36 billion gallons of oil equivalent in 2022.Cellulosic material is considered a renewable and environmental improved alternative source for energy production. Sorghum (Sorghum bicolor L.) could provide food and cellulosic feedstock production in agricultural lands. However, the impacts of removing cellulosic biomass on soils must not be ignored. The types of sorghum evaluated were: grain sorghum - NK300 (GS), high biomass forage sorghum - SS 506 (FS), and photoperiod sensitive forage sorghum - 1990 (PS). These 3 different varieties and a forage corn (Zea mays L.) - Pioneer 31G65 were grown in 2008 and 2009 under irrigated and non-irrigated treatments, and under two different tillage systems: conventional and conservation tillage. Results after two years of cropping showed that Soil organic carbon (SOC) increased near soil surface, but it decreased from 0.40 - 0.45 m. SOC losses were higher in conventional than conservation tillage. Total Nitrogen in soil (N) increased in all soil depths (0 - 0.50 m) due to high N application. N was also higher in deep layers due to percolation which could result in environmental degradation. Additionally, soil consolidation was observed after two years of cropping. Bulk density (Bd) values increased at all depths, but those values were always lower than threshold for soil compaction.  PS showed significant lower Bd than corn in superficial layers (0.05 - 0.20 m). Irrigated and conventional plots had lower Bd in some evaluated layers. Cone Index (CI) values also showed improved soil conditions at in-row positions for conservation plots, with restrictive layers being found at depths of 0.15 m for conventional plots. Therefore, conservation tillage, photoperiod sensitive sorghum (1990) - PS and reduced N applications were recommended in order to improve soil condition and prevent environmental degradation.