Mineral content of grasses grown for seed in low rainfall areas of the Pacific Northwest and analysis of ash from gasification of bluegrass (Poa pratensis L.) straw

Authors: Banowetz, Gary; Griffith, Stephen; El Nashaar, Hossien

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2008
Publication Date: 3/27/2009
Citation: Banowetz, G.M., Griffith, S.M., El Nashaar, H.M. 2009. Mineral content of grasses grown for seed in low rainfall areas of the Pacific Northwest and analysis of ash from gasification of bluegrass (Poa pratensis L.) straw. Energy and Fuels. 23:502-506.

Interpretive Summary: Straw from grass seed production in the low rainfall regions of the Pacific Northwest has potential to be used as feedstock for biofuel production. Most straws, however, contain large quantities of minerals that prevent their efficient use in high temperature processes to convert the straw to energy. Although plant breeders improve grasses for many other purposes, the potential of using conventional plant breeding to select grasses with reduced mineral content is not known. This study quantified the concentration of minerals in a multiple varieties of Kentucky bluegrass, tall fescue and perennial ryegrass and found considerable variation in mineral accumulation that may be exploited by plant breeders to improve the biofuel quality of straw.

Technical Abstract: Straw resulting from grass seed and cereal grain production represents a potential supply of biomass for energy production. The low-density distribution of this biomass in many locations suggests that distributed small-scaled thermochemical technologies may provide an economic conversion approach. The utility of straw as feedstock for thermochemical approaches is impacted by the presence of “anti-quality” mineral constituents that form slag at commonly used operating temperatures. Slag reduces the useful life of thermochemical reactors. Harvesting straw also removes mineral fertilizer components and soil carbon that impact the sustained production of subsequent crops. The objective of this research was to characterize mineral accumulation by diverse grasses produced for seed at two contrasting locations in the low rainfall region of the Pacific Northwest to determine the following; 1) whether genotypic differences in mineral accumulation by these grasses provide opportunity for genetic improvement of feedstock characteristics and, 2) fertilizer and carbon values of straw as conservation residue. Significant (P < 0.01) differences in the accumulation of most minerals that were analyzed occurred between genotypes of Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.) and tall fescue (Schedonorus phoenix (Scop.) Holub). Mineral accumulation varied between species and was dependent upon the location at which the plants were grown. On average, harvested straw contained 26kg Mg-1 of potassium, 0.85 kg Mg-1 of phosphorus, and 0.34 kg Mg-1 of carbon. Much of the potassium and phosphorus are recovered in ash produced by a small-scale gasification reactor.