Effects of probiotics on soil microbial activity, biomass and enzymatic activity under cover crops in field and greenhouse studies

Intensive use of agro-chemicals over the past few decades has increased land productivity, however, frequent application of agro-chemicals has also resulted in some negative impacts on the environment and soil microbial biodiversity. Use of alternative management such as probiotics is believed to promote soil microbial biodiversity and enzymatic activity. This research was conducted at the Natural Resources Conservation Service Soil Health Farm, Chariton County, Missouri to quantify probiotic effects on soil biological diversity and activity. Prior to 2012, the site was comprised of conventional corn (Zea mays L.)-soybean (Glycine max L.) rotation with tillage and chemical fertilizer use. Soil amendment with probiotics (Bio-Ag) included a non-treated control, and dosages at 60 L probiotic ha−1 year−1; 90 L probiotic ha−1 year−1; and 120 L probiotic ha−1 year−1 with three replications. Two equal split soil applications of probiotics were applied in September 2013 and May 2014. Soil samples were collected in August (pre-treatment), September 2013 and June 2014 from 0 to 6 cm depth. A greenhouse study was conducted using soil cores. Treatments were similar those in the field study except the low dose was excluded and higher dose of 150 L ha−1 year−1 was used. Soil microbial biomass and community structures were analyzed using phospholipid fatty acid analysis. Standard soil enzyme assays were used to assess microbial activity. Saprophytic fungi, protozoa and rhizobia biomass were significantly higher with 120 L probiotic ha−1 year−1 dose than control in the field study (p < 0.10). Total microbial biomass was significantly increased and saprophytic fungi biomass was more than two times higher with the 120 L ha−1 year−1 dose compared with the control in the greenhouse study at the December 2014 sampling. In the field study, principal component analysis revealed that PC1 and PC2 accounted for 62 % of total variance. Increasing trends in the values of soil fungal communities, rhizobia, dehydrogenase, β-glucosaminidase and fluorescein diacetate hydrolase with the 120 L probiotic ha−1 year−1 dose implies that probiotics can be used to improve soil quality indicators.