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

Straw residue from grass seed production, along with clippings from turfs derived from that seed, represent a potential supply of feedstock for bioenergy production. Harvesting straw from these production systems removes minerals, including macronutrients and carbon that ultimately must be replaced to sustain soil quality and subsequent crop production. In addition, certain mineral constituents of straw contribute to slag formation at common operating temperatures in thermochemical reactors. The objective of this research was to determine whether genotypic differences in the concentrations of minerals that impact thermochemical conversion and represent macronutrient loss existed within and among Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and tall fescue [Schedonorus phoenix (Scop.) Holub]. Grasses were grown at two contrasting locations in the low rainfall region of the Pacific Northwest, and mineral analyses were performed on vegetative tissues from each. Differences in the concentration of most minerals occurred among varieties of Kentucky bluegrass and between the three species. Mineral concentration was dependent upon the location at which the plants were grown but not always correlated with soil content of the respective mineral. On the basis of the average amount of straw available after conservation requirements have been met, we estimate that straw harvest removes 48-96 kg of potassium ha(-1), 2-10 kg of phosphorus ha(-1), and 662-1029 kg of carbon ha(-1). Mineral analyses of ash derived from gasification of Kentucky bluegrass straw showed that nitrogen, phosphorus, potassium, and carbon were recovered in the ash and represented a potential soil amendment. Dioxin and heavy-metal concentrations in the ash were very low.