Utilization of C3 Grasses for a Dual Forage and Biomass Production System with Limited Irrigation.

Abstract The growth of the green house gases (GHGs) CO2, CH4 and NOx GHG’s has been attributed as the cause of the climatic warming during the industrial era and current fossil fuel energy systems have serious environmental, economical, and political implications. There is a strong link between desertification and global warming, and it is feared that risks of desertification are likely to be intensified with the predicted climate change. Net Energy Balances of cellulosic ethanol from perennial Switchgrass ( Panicum vergatum) was modeled to have >700% energy. Agriculture and rangeland restoration have been indentified for GHG mitigation strategies, with 30% of CO2 offsets coming from biomass fuel production. The 2007 Energy Independence Act is calling for 36 billion gallons of biofuels, with 21 Bgal coming from advanced biofuels. The DOE has designed the Office of Biomass Program (OBP) to secure national energy needs by developing technologies that will utilize biomass resources. Switchgrass, a C4 grass species, was chosen by the DOE as the model crop for cellulosic biofuels because of the plant’s perennial nature, high WUE, wide range of exploitable genetics, and its ability to be grown in diverse regions. The specific goal for cellulosic ethanol is to make it cost competitive with grain ethanol as a transportation fuel blend by 2012. Cool season or C3 species are major contributors to forage production because of superior digestibility and high feed value. In relation to cellulosic biofuel, the high digestibility of C3 forages is directly correlated to reduced lignin content which is a primary barrier to bioconversion and plant tissues with reduced amounts will have greater conversion efficiencies. Establishment is reportedly difficult with Switchgrass and could be more attainable with the hardier C3 grasses. Smooth Bromegrass (Bromus inermis Leyss) was one of the few cool-season forage grasses to survive droughts and gained popularity for revegetation of drought-damaged grasslands and marginal croplands throughout the Great Plains. Meadow Brome (Bromus riparius Rehm.) is utilized for less productive agricultural land which is often associated with periods of reduced irrigation, soil salinity, and low fertility. Livestock production is an important part of the economy in agricultural communities, and producers could be pushed further onto marginal lands with increased biomass production; making C3 forages ideal for dual systems to decrease competition. In semi arid rangelands drought is an inherit risk. Water availability greatly influences yields, and forage producers have been utilizing production differences in C4 and C3 to allocate seasonal supplies of high quality forage to livestock. For these reasons 15 different species of cool season grasses were evaluated for biofuel feedstock qualities through ADF, NDF, CP and yield analysis under varying irrigation treatments and harvest timings and how these factors effect optimal biomass production. By delaying harvest timings from June 1st to June 21st there was a 35% average yield increase, and a 8% and 10% decrease in forage quality for NDF and ADF by with Species effect. CP had the greatest net change of 29% from June 1st to June 21st, decreasing with delayed harvest. There was statistical significance between the two re-growth periods related to harvest timing in which delayed harvest reduced tillers and decreased resilience under limited irrigation. Re-growth from June 1st had 49% greater yield then re-growth from June21st with an average full season irrigation yield of 370 kg/ha. Full season irrigation greatly influenced yields for both Regrowth cuttings but there was a stronger Species X Irrigation effect for the June 21st re-growth which is demonstrated in the reduced yields for limited irrigation. The June 21st re-growth full season irrigation harvest average= 185 kg/ha and limited irrigation yields fell to 85 kg/ha. The June 21st re-growth had a 54% reduction in yields between the full and limited irrigation treatments, while the earlier June 1st regrowth limited irrigation was only reduced by 45%.