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Fertilizers are used in many agricultural systems as a means to bolster crop yields by temporarily increasing the nutrient content of arable soils. Inconsistent amounts of nutrients leach from cropland depending on fertilizer, soil, crop type, and various other factors. The nutrients dispersed by fertilizers send microbial growth into overdrive similar to eutrophication of water bodies. This project examined the effect of a fertilizer (30% N-10% P-10% K) on the growth of three known plant-growth-promoting rhizobacteria: Rhizobium leguminosarum, Rhodospirillum rubrum, and Bacillus subtilis. Strains were inoculated individually and coinoculated in sterile soil treated with three treatments of increasing fertilizer concentration. Microbial growth was quantified by analyzing percent coverage of plates made from dilutions of inoculated soil. A positive correlation was found between microbial growth and fertilizer concentration when all strains were inoculated individually, but the results from coinoculations did not produce a consistent relationship. Results from individual inoculations of R. leguminosarum suggest an intermediate fertilizer concentration where microbial growth was maximized.
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Link, Samuel Stefan, "The Effect of Common Fertilizers on the Abundance of Plant-Growth-Promoting Rhizobacteria" (2013). Senior Projects Spring 2013. 54.