Effects of Fire and Grazing Driven Heterogeneity on N Cycling in Tallgrass Prarie

Abstract

The purpose of this study was to evaluate the combined interactive effect of fire and grazing on N availability in tallgrass prairie. To address this, data from recently burned, one year since fire, and two years since fire patches within a grazed shifting mosaic landscape were compared. To evaluate a shifting mosaic, a landscape that had similar grazing pressure but where the entire area was burned annually was also compared. Total soil inorganic N (NH4+-N + NO3--N) and total plant N recovered from a growth chamber experiment with red winter wheat (Triticum aestivum L. cv. Jagger) were measured to evaluate N availability. In an attempt to explain the observed patterns of N availability, soil microbial biomass C (MBC) was measured using the chloroform fumigation extraction method along with selected soil properties as soil microbial biomass values are often influenced by inherent landscape variability. A significant pulse in N availability was observed as a result of focal disturbance while the homogenous fire-grazing regime had an intermediate level of N availability. Fire-grazing regime had no effect on soil microbial biomass values and multiple regression analysis revealed that pH and organic C were dominant variables explaining the variance. Overall, focal fire and grazing disturbance produced patterns of N availability that are more similar to grazing lawn studies where N availability is enhanced by periodic focal grazing by large ungulates.