Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2011
Publication Date: October 1, 2011
Citation: Knoll, J.E., Strickland, T.C., Hubbard, R.K., Malik, R., Anderson, W.F. 2011. Biomass production and nutrient utilization of perennial grasses under no inputs in south Georgia. BioEnergy Research. 5:206-214. Interpretive Summary: Increasing energy demand with reduced reserves, fluctuations in fuel prices, and concerns about climate change caused by burning of fossil fuels have brought about renewed interest in producing energy from renewable sources. Of particular interest is bioenergy, which is energy derived from plant biomass, either through direct combustion for power generation, or through conversion to liquid fuel, such as ethanol. Warm-season perennial grasses have the greatest potential for sustainable biomass production in the Southeast, and reported to have the ability to produce feedstock on marginal lands. This study was initiated in fall 2005 at Tifton, GA, to assess the performance of perennial grasses with no supplemental irrigation or fertilizer, to see which grasses perform best under marginal conditions in the Southeast. The test included one energycane (Saccharum sp.), two accessions of napiergrass (Pennisetum purpureum Schum.), two experimental lines of switchgrass (Panicum virgatum L.), and three giant reed (Arundo donax L.) clones. Each winter, biomass dry matter (DM) yield, moisture, and biomass nutrient contents were analyzed. Napiergrass yields averaged 31.6 Mg DM/ha for the first two years, and energycane averaged 25.5 Mg DM/ha for the first three years. Though lower yielding, switchgrass had good biomass quality, tending to be lowest in nitrogen, ash, and moisture at harvest, factors making it suitable for combustion. Yields declined significantly in the fourth season, suggesting that residual nutrients in the soil were being used up. Napiergrass took up large quantities of potassium in the first season (704 kg K/ha), but only about half as much the next season with similar DM yields. Energycane was found to utilize potassium more efficiently than napiergrass, taking up less of this nutrient while still producing similar yields. Soil cores were collected in 2009 to a depth of 1 m to assess possible changes in soil nutrients, and to estimate root biomass. Some evidence of potassium depletion in the soil profile was found for napiergrass in the soil cores, but no evidence of nitrogen depletion was observed in the soil. Biomass nitrogen content was, however, correlated with DM yield for the energycane, one napiergrass, and one switchgrass, suggesting that this nutrient was also limiting in later seasons. Based on the nutrient uptake data, future studies of napiergrass should focus fertilizer rates around 200 kg N/ha and 300 kg K/ha. Energycane studies should focus on rates around 100–150 kg N/ha and 200 kg K/ha. Roots were most numerous in the upper soil layer of the cores, but were also found at 1 m depth. Roots beyond this depth could possibly tap deep nutrient reserves, but this needs to be investigated. Properties of the various biomass feedstocks for conversion to ethanol will be investigated in future studies.
Technical Abstract: Warm-season perennial grasses have the greatest potential for biomass production in the Southeast. The larger root systems of perennial crops should be able to adapt to lower inputs of water and fertilizer, and should also contribute to soil carbon sequestration. This study was initiated in fall 2005 at Tifton, GA, to assess the performance of perennial grasses under rainfed conditions with no fertilizer inputs. The test consisted of four replications in a randomized complete block design, and included the following entries: two energycanes (Saccharum sp.) US 01-012 and L 79-1002; two Napiergrasses (Pennisetum purpureum Schum.) ‘Merkeron’ and N51; two switchgrasses (Panicum virgatum L.) GA-001 and GA-993; three giant reeds (Arundo donax L.) ADS, ADE, and ADF; and Erianthus arundinaceum. Total shoot biomass was harvested and weighed each year (2006 – 2008) in December, and was analyzed for total carbon and nitrogen content. Soil samples were collected in spring 2007 and 2008 to assess possible changes in soil carbon and nitrogen. For most entries, dry matter (DM) yield was highest in the second year, although energycane L 79-1002 maintained exceptional yields throughout the first three years, averaging 23,115 lb DM/acre. Averaged over three years, DM yields of energycanes, Napiergrasses, and Erianthus were significantly higher than switchgrasses and giant reeds. Switchgrasses and giant reeds were not significantly different in DM yield, but switchgrasses had higher nitrogen use efficiency, based on the nitrogen content of the harvested plants. From 2007 to 2008, no significant changes in soil carbon or nitrogen were observed.