Research has yielded conflicting results on the effects of high-intensity grazing on soil health. The soil microbial community drives nutrient availability, but there are knowledge gaps in how soil microbes respond to grazing disturbance, as well as how above- and belowground processes interact to support vegetation recovery immediately following defoliation. The objectives of this study are to detect the immediate response of the soil microbial community to disturbance and monitor corresponding responses of vegetation and nutrient cycling.
A grazing study was implemented at the Agricultural Experiment Station in Laramie, Wyoming. Twelve adjacent ½-acre paddocks were grazed according to three treatments in a randomized complete block design: a high-intensity, short-duration treatment (HI), a low-intensity, medium-duration treatment (LO), and a no-grazing control (NG). Vegetation and soil samples were taken 1 week before grazing (baseline data), 24 hours after grazing, 1 week, and 4 weeks after grazing.
Microbial functional diversity was quantified by extracellular enzyme assays, which detect the activity of carbon, nitrogen, and phosphorus cycling enzymes. Microbial biomass was measured using chloroform-fumigation incubation, and biogeochemical parameters included dissolved organic carbon and nitrogen. Vegetation biomass and recovery was monitored with a rising plate pasture meter.
Results/Conclusions
Results indicate that microbial biomass C differed significantly between the grazing treatments (high-intensity, short-duration grazing and low-intensity, medium-duration grazing) and the no-grazing control. Extracellular enzymatic activity relative to microbial biomass C was significant between the grazing treatments and the no-grazing control for the lignolytic enzymes and phosphorous cycling enzymes. Dissolved organic nitrogen differed between the LO grazing treatment and the HI grazing treatment, and between the HI grazing treatment and the no-grazing control. Vegetation recovery, the growth of vegetation over time following grazing, was higher in the HI grazing treatment than both the LO grazing treatment and the no-grazing control. These results indicate that grazing may have an immediate effect, detectable after twenty-four hours following grazing, on soil nutrient availability and soil microbial activity, and that vegetation recovers faster following high-intensity, short-duration grazing than low-intensity, medium-duration grazing.