Soil Microbial Community Changes After Oilseed Meal Application.

Oilseed meals (co-products remaining after oil extraction) have been successfully used as organic fertilizers and biofumigants in the past, but relatively few studies have investigated their impact on soil microbial communities. We examined the effect of  oilseed meals from jatropha (Jatropha curcas), camelina (Brassica camelina), and flax (Linum usitatissimum), along with wheat (Triticum aestivum L.) straw as a comparison, on soil microbial community changes in a Weswood loam soil at 0, 1 and 5% (w/w) rates of application. After 3, 7, 14, and 28 days of incubation at 25°C, soil microbial DNA was extracted and amplified through qPCR using primers targeting total populations of bacteria and fungi. All tested oilseed meals and wheat straw significantly increased soil bacterial (1.5- to 7.7-fold) and fungal populations (249.5- to 1494.0-fold) at both application rates compared to an unamended control. Fungal populations tended to peak after 3 d while bacterial populations were more variable, peaking after 3 (camelina and flax) to 14 d (jatropha and wheat).  Bacterial:fungal ratios were reduced in all oilseed meal- or straw-amended samples, relative to the control, suggesting that decomposition was primarily due to fungal populations. These results indicated that selected oilseed meals significantly enhanced both soil bacterial and fungal populations after being applied to soil, although fungal populations were increased to a greater extent.