Soil Microbial Communities Affected by Different Oilseed Meals and a Crop Residue.

Land application of oilseed meals, the co-product after oil extraction potentially provides an important disposal method for this bioenergy byproduct and it has the added benefit of supplying nutrients to the soils. However, some of these meals contain biochemicals, such as glucosinolates, which may inhibit key populations of soil microorganisms. Little information currently exists on how oilseed meals affect soil microbial ecosystems. In this study, different amounts (0.5, 1, and 5% w/w) of jatropha, camelina, and flax seed meals and wheat biomass were added to laboratory microcosms containing Weswood loam soils (fine-silty, mixed, superactive, thermic, Udifluventic Haplustepts). A variety of methods including microbial biomass, quantitative PCR (qPCR) assays, phospholipid fatty acid profiles (PLFA), whole soil fatty acids methyl esters (FAME) analysis and Biolog EcoPlates were used to investigate community changes over an incubation period of 19 weeks. Total microbial biomass dramatically increased in all treatments with the greatest increase occurring with the oilseed meals. For the 0.5 and 1% rates of addition, biomass levels returned to the background levels within 2 wks except for the wheat. Biomass remained higher than controls at the 5% application rate until the end of the incubation. Seed meal amendments selected distinct microbial communities with different physiological profiles and compositions of fungi, bacteria and actinomycetes. Addition of oilseed meals generally increased the abundance of bacterial and fungal biomarkers but resulted in lower bacteria to fungi ratios compared to wheat treatments as indicated by PLFA results. Consistently, based upon qPCR, addition of oilseed meals resulted in lower ratios of bacteria:fungi indicating community composition changes.