GROWTH AND BIOMASS OF SWEET SORGHUM BIOFUEL FEEDSTOCK IN NORTH ALABAMA

ABSTRACT Sweet sorghum (Sorghum bicolor L. Moench) which is primarily grown as a silage crop in the U.S., has potential as a biofuel feedstock in areas where the seasonal climate is not suitable for sugar cane production. Other useful products from the crop include bagasse which can be used as a stock feed and charcoal. Growth parameters and biomass production of sweet sorghum under conventional tillage (CT) and no-till (NT) systems were evaluated under rainfed conditions over three growing seasons from 2012 to 2014 on a Decatur silt loam soil at Hazel Green, Alabama. Plant heights in CT averaged 1.97 m compared to 1.59 m in NT system (p<0.001). Stem biomass yields averaged 8.15 t/ha and 7.73 t/ha, respectively, in CT and NT system at physiological maturity. Similar figures for root biomass were 4.36 and 4.50 t/ha, respectively in CT and NT system. The differences in stem and root biomass yields under CT and NT were not significant. Stem biomass yield was significantly correlated (r < 0.001) to soil moisture content. The anticipated impact of this project is the development of a new generation of student leaders ready to support the biofuel industry. In addition, this project will provide science-based knowledge and information which can be used as invaluable tools in efforts to develop best management practices (BMPs) for profitable and environmentally sustainable biofuel production strategies in the southeast U.S.

Hakeem Broomfield, Ermson Z. Nyakatawa, Ernst Cebert, David A. Mays

Department of Biological and Environmental Sciences, Alabama A&M University, 4900 Meridian Street, Huntsville, AL

Objectives of the Study

1. To investigate growth, physiological parameters, and biomass yield of sweet sorghum biofuel feedstock production under conventional and conservation tillage practices

2. To investigate the effects of conservation tillage and fertilizer management practices on soil carbon and nitrogen dynamics in plots under sweet sorghum for biofuel feedstock production systems in north Alabama. 3. To asses the effects of conservation tillage and fertilizer management practices on , organic and, inorganic management practices on soil heavy metal concentration.

Figure 1. Sweet sorghum plants at vegetative growth stage, Hazel Green AL

INTRODUCTION

Sweet sorghum (Sorghum bicolor L. Moench) has several beneficial features which make it a viable source for bioenergy. These include its adaptability to marginal sites and drought conditions (Marta et al., (2014), its highly efficient photosynthetic pathway, and very high efficiency in the utilization of soil nutrients (Cifuentes, et al., 2014). Furthermore, sweet sorghum is selected for its capacity to accumulate soluble sugars into the juice and stalk that can be extracted mechanically and then fermented for ethanol production. The goal of this study is to assess the performance and environmental sustainability of intensive sweet-sorghum production as a biofuel feedstock in the South-east U.S.

References Marta, A. D., Mancini, M., Orlando, F., Natali, F., Capecchi, L. Orlandini, S. 2014. Sweet Sorghum for bioethanol production: Crop responses to different water stress levels.” Biomass and Bioenergy 64: 211–219.

Cifuentes, R., Bressani, R., and Rolz, C. 2014. The potential of sweet sorghum as a source of ethanol and protein. Energy for Sustainable Development 21:13-19.

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MATERIALS AND METHODS

Study Location The study is being done at Winfred Thomas Agricultural Experiment Station, Hazel Green, Alabama (latitude 34o 89’ N and longitude 86o56’ W), which is located in major row crop and poultry producing area in the Tennessee Valley region of north Alabama. The study site’s soil composition is a Decatur silt loam (fine, kaolinitic, thermic Rhodic Paleudult), with clay content up to about 30%. Treatments The treatments consist of two tillage systems: conventional tillage and no-tillage system with cover crop. Nitrogen treatments consisting of three nitrogen (N) levels, (1) control (0 kg N/ha), (2) poultry litter (100 kg N/ha), and (3) ammonium nitrate (100 kg N/ha) were applied in 2014. A grass fallow treatment which is not tilled or planted with a crop was also included as an absolute control. The list of treatments to be used in the study is shown in Table 1.

Trt. Tillage system N treatment 1 Conventional tillage (CT) 0N (control)

2 Conventional tillage (CT) Poultry litter (PL)

3 Conventional tillage (CT) Ammonium nitrate (AN)

4 No-till (NT) 0N (control)

5 No-till (NT) Poultry litter (PL)

6 No-till (NT) Ammonium nitrate (AN)

7 Grass fallow (GF) 0N (control)

Table 1. List of treatments for sweet sorghum study at Hazel Green, AL

RESULTS AND DISCUSSION Sweet sorghum plants averaged over three years from 2012 to

2014 in CT system were, respectively, 8cm, 19cm, 46cm, and 38cm taller than those in NT system at 4, 6, 8, and 10 weeks after emergence (Fig. 3). Similarly, canopy cover for sweet sorghum plants over the same period in CT system were, respectively, 11%, 23%, 13%, and 16% greater than those in NT system at 4, 6, 8, and 10 weeks after emergence.

The only growth parameter which were greater in NT system compared to CT during the study period was root biomass which was 0.14 tons/ha greater at 10 weeks after emergence. Stem biomass of sweet sorghum plants in CT system were, respectively, 1.55 tons/ha and 2.57 tons/ha higher than those in NT system at 6 and 8 weeks after emergence. There was, however, no significant differences in stem biomass of sweet sorghum plants in CT and NT systems at 4 and 10 weeks after emergence (Fig. 3).

The consistently better growth of sweet sorghum plants in CT system compared to NT system was attributed to consistently better

ACKNOWLEDGEMENTS Funding for this project is provided by the USDA NIFA, Integrated Biomass Supply Systems (IBSS) project, Grant # 2011-68005-30410

Figure 2 . Conventional and no-till plots for sweet sorghum study (left) and flowering sweet sorghum plants at Hazel Green, AL (right)

Plant height Leaf Area Index

Canopy cover Stem biomass

Figure 3. Growth parameters and biomass yield of sweet sorghum plants in conventional and no-till systems at Hazel Green, AL

soil tilth and seedbed preparation due to tillage in CT system. This was further corroborated by the fact that seed germination and seedling emergence were consistently earlier and faster in CT system compared to NT system thereby giving the plants in NT system an earlier start on growth and development.

These results with sweet sorghum suggest that in order to take advantage of NT as a best management practice for sweet sorghum production on the silt clay soils, strategies to improve soil tilth via organic matter inputs such as addition of animal manures and residue incorporation need to be adopted.

Data Collected Sweet sorghum was planted in May-June each year. Growth analysis to assess growth and biomass yield production of sweet sorghum was performed every two weeks from seedling emergence to maturity. Other data being collected include soil chemical properties and soil environmental variables such as temperature and moisture