Impact of Grazing/Non Grazing Winter Annuals On Soil Microbial Biomass C, Microbial Diversity, and Nutrient Cycling Enzymes.

Impact of grazing/non grazing winter annuals on soil microbial biomass C, microbial diversity, and nutrient cycling enzymes

 Diversification of farming practices in the southeastern US, prone to experiencing water deficits, is imperative. We integrated cattle and perennial grasses with row crops (2 years of bahiagrass followed by peanut then cotton) to understand the effects of grazing on soil properties that could likely be a driving factor for increased crop yields especially under water-limiting conditions. Surface soil (0-15cm) cores were composited to obtain a sample representing each treatment. After initial processing, microbial biomass carbon, and enzymes involved in C, P, N, and S cycling were compared in grazed and non-grazed treatments under irrigated and non-irrigated conditions. Distribution of microbial communities was studied by carrying out fatty acid methyl ester (FAME) analysis and automated ribosomal intergenic spacer analysis (ARISA). Microbial biomass C in grazed plots of the non-irrigated treatments were significantly greater (152-200 mg C/kg soil at 0-5, 5-10, and 10-15 cm respectively) than non-grazed plots (88-100 mg C/kg soil at the same depth increments). The percentage of total organic C that occurred as microbial biomass C in these plots at all 3 depth levels (0-5, 5-10, and 10-15 cm) was significantly greater in the grazed plots (1.66-2.07%) than non-grazed plots (0.8-0.85%). Activities of beta glucosidase (C cycling), acid and alkaline phosphatases (P cycling), and arylsulfatase (S cycling) were all significantly greater in the grazed plots. FAME analyses indicated an increase in Gram positive bacterial and fungal populations in grazed plots under certain crops. ARISA analyses indicated that the crop influenced microbial communities more than grazing itself.