Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2010
Publication Date: 9/20/2010
Citation: Cantrell, K.B., Bauer, P.J., Ro, K.S. 2010. Utilization of summer legumes as bioenergy feedstocks. Biomass and Bioenergy. 34:1961-1967.
Interpretive Summary: One tropical legume, sunn hemp, yields large amounts of biomass that can potentially be used in the southeastern United States as a bioenergy crop. This legume was compared to another common summer legume, cowpeas. When comparing the two legumes, the biomass yield (mass per area) and subsequent energy yield (energy per area) were greater for sunn hemp. Even though for sunnhemp the ash content was greater leading to greater amounts of unconverted material, sunn hemp was lower in certain plant minerals known to decrease the bioenergy conversion efficiency. Sunn hemp degraded under a non-oxygen environment at higher temperatures and released more convertible material.
Technical Abstract: Sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume—cowpeas (Vigna unguiculata), sunn hemp was superior in biomass yield and subsequent energy yield. Sunn hemp had 10.7 Megagrams per hectare of biomass with an energy content of 19.0 Megajoules per kilogram after 12 weeks of growth in one year of the study. This resulted in an energy yield of 204 Gigajoules per hectare. The energy content was 6% greater than that of cowpeas. Even though sunn hemp had a greater amount of ash, plant nutrient concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release greater amounts of volatile matter.