A New Spin on an Old Crop for Bioenergy: Sorghum
Type of Degreethesis
Agronomy and Soils
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According to Renewable Fuels Standard (RFS) – Energy Policy Act of 2005, the U.S. must reduce foreign oil dependence, where the target is to produce 36 billion gallons of oil equivalent in 2022 (RFA, 2010). Cellulosic material is considered an alternative source for bioenergy production, because it is renewable and environmentally friendly (Peters and Thielman, 2008). Annual crops, such as sorghum (Sorghum bicolor L.) can be cultivated in current row-crop production systems, which could provide grain and cellulosic feedstock production in Southeastern U.S. However, the impacts of removing cellulosic biomass on agricultural soils must not be ignored, and sorghum biomass has relatively high moisture content which should be dried before transported to reduce costs. Different experiments were established at the E.V. Smith Research Station, Shorter, AL to evaluate quantity and quality of sorghum biomass production, to monitor soil impacts due to biomass production/removal, and determine the best approach to drying sorghum biomass. Three types of sorghum: grain sorghum – NK300 (GS), high biomass forage sorghum – SS 506 (FS), and photoperiod sensitive forage sorghum - 1990 (PS) and a forage corn (Zea mays L.) – Pioneer 31G65 were grown for two consecutive years (2008 and 2009) under irrigated and non-irrigated treatments, and under two different tillage systems: conventional (total disked area, 0.15 m depth) and conservation tillage (in-row subsoiling, 0.30 m depth). The results indicated that irrigation affected aboveground dry matter (ADM) positively in both years, but conservation system improved ADM production only in 2009. Holocellulose, lignin and ash content differences among crops for both evaluated years were lower than 8.3%, 2.0% and 1.9 % respectively, and they were considered minor. PS was considered the best crop for ADM production, respectively, 26.04 and 30.13 Mg/ha at 18 and 24 weeks after planting in 2008. ADM production in 2009 decreased due to leaf losses caused by Anthracnose (Colletotrichum graminicola) disease which affected all sorghum varieties. Furthermore, changes in soil characteristics were detected after 2 years of cropping. Soil organic carbon (SOC) increased near soil surface (0.10 – 0.15 m), but it decreased from 0.40 – 0.45 m. SOC losses were higher in conventional than conservation tillage. Total nitrogen in soil (N) drastically increased in deep layers due to percolation. Additionally, bulk density (Bd) values increased at all evaluated depths. Irrigated plots had higher Bd than non-irrigated plots at both 0.05 – 0.10 and 0.20 – 0.25 m soil layers. And cone index (CI) values showed restrictive layers at depths of 0.15 m for conventional plots. Therefore, conservation tillage and photoperiod sensitive sorghum (1990) – PS were recommended. In another experiment, sorghum-sudan hybrid was harvested with two different headers on a self-propelled windrower: a Massey Ferguson 9145 (sickle) and a Massey Ferguson 9185 (disc). The disc header was comprised of two pairs (rear/front) of metal conditioner rollers which used three different pressures (0, 3500, and 7000 kPa), and two different gaps (0 and 0.02 m). Sorghum-sudan biomass moisture content (%) was evaluated daily until it remained constant. Results revealed that the higher pressures and smaller gaps resulted in faster drying of biomass. The best settings for the disc header were “7000 kPa – 0 m” or “7000 kPa – 0.02 m” which showed, respectively, moisture content levels of 13.6 % and 16.8 % after 14 days. These results indicate that proper setting of the disc header including properly setting the pressures and gaps are important to achieve optimum drying of sorghum biomass.