Short-term effects of soil amendment with meadowfoam seed meal on soil microbial composition and function

Meadowfoam (Limnanthes alba Hartw. ex Benth) seed meal (MSM), a by-product of meadowfoam oil extraction, has a secondary metabolite known as glucosinolate glucolimnanthin. MSM applied as a soil amendment has been reported to have herbicidal and fertilizer properties. Experiments were conducted over 28 days to evaluate short-term effects of a MSM application on soil microbial communities. MSM was applied to soil as either a full or a split application. In addition to MSM and untreated control treatments, urea was used as a N source to account for the fertilizer effect of the seed meal. Urea was applied either as a full or a split rate on the same schedule as MSM. Soil microbial activities were not different between the full and the split rate applications of MSM. After day 7 following MSM application, carbon-source utilization of microbial communities of MSM was different from the urea and control treatments. Microbial communities in MSM treatments utilized complex carbon sources to a relatively greater degree than microbial communities in urea or control treatments. The C and N inputs from MSM increased the gross metabolic activity of the mixed microbial population. Basal respiration was stimulated and microbes reallocated carbon input to biomass and enzyme production. Within 7 and 14 days after MSM application, the reallocation occurred quickly and microbial biomass increased by at least 80% for C and 95% for N compared to the untreated control. In the short-term, MSM treatments affected nutrient dynamics, and the soil microbial structure and function. The effects of MSM application on the composition of bacterial and fungal communities warrant additional study. (C) 2015 Elsevier B.V. All rights reserved.