The tropical legume sunn hemp (Crotalaria juncea) could be a good biofuel crop for farmers in the southeast, according to new ARS research. Photo: Forest & Kim Starr.
Work by scientists at the U.S.
Department of Agriculture (USDA) suggests that farmers in the Southeast could
use the tropical legume sunn hemp (Crotalaria
juncea) in their crop rotations by harvesting the fast-growing
annual for biofuel. The study, which was conducted by Agricultural Research
Service (ARS) scientists in Florence,
S.C., supports the USDA priority
of finding new sources of bioenergy.
ARS agricultural engineer Keri
Cantrell, agronomist Philip Bauer, and environmental engineer Kyoung Ro all
work at the ARS Coastal Plains Soil, Water, and Plant
They compared the energy content of sunn hemp with cowpea (Vigna unguiculata), another common
regional summer cover crop, in 2004 and 2006.
Both crops were grown in
experimental plots near Florence
and were harvested on the same day three times in each study year. The last
harvest for both years was conducted right after the first killing freeze of
the season. The scientists measured potential energy production of both
feedstocks via direct combustion. This provided the feedstocks’ higher heating
value (HHV), which indicates how much energy is released via combustion.
In 2004, when there was
ample rainfall, the resulting sunn hemp biomass yield totaled more than 4.5
tons per acre. This is equivalent to 82.4 gigajoules (GJ) of energy per acre,
close to the energy contained in 620 gallons of gasoline and well in the
ballpark of other bioenergy crops, which have yields of anywhere from 30 to 150
GJ per acre.
The HHV for sunn hemp
biomass exceeded the HHV for switchgrass, bermudagrass, reed canarygrass, and
alfalfa. Although reduced rainfall resulted in lower hemp biomass yields in
2006, sunn hemp’s HHV for both study years was 4 to 5% greater than the HHV of
Results from the study
were published in Biomass and