Short-Term Effects of Prescribed Burn Frequency On Rangeland Soils.

We investigated the short-term effects of prescribed burn treatments on soil chemical properties, microclimate variables, and soil respiration rates at the Natural Resource Management Research Station in Lubbock, TX. Burn treatments included the use of fire in different seasons (summer and winter) and at two frequencies (once in two years, or once a year for two years) from 2008-2010. Soil samples (0-2.5cm) were collected pre-burn, 30-min, and 24-, 48-, and 168-hours following burn events in summer 2009 (S09) and Winter 2010 (W10). Samples were analyzed for soil ammonium-N (NH4+-N), nitrate-N (NO3--N), pH, total nitrogen (TN) and carbon (TC), soil moisture, temperature, and carbon dioxide (CO2) flux. The effect of burn frequency only had an impact on soil NH4+-N concentrations and this impact was different depending on season. Soil NH4+-Nconcentrations increased (p=0.006) in plots burned in two consecutive summers compared to those found in the single summer burn whereas, the opposite was observed in soils burned in the winter. Short-term changes in soil NH4+-N concentrations were measured within samples collected 30 minutes post-burn and levels returned to pre-burn status within 168-hr (7-days) following the S09 and the W10 burns. Soil temperature was higher (p<0.0001) following the S09 burn compared to control plots and remained higher through the 7-day sampling period. However, the same response in W10 burn was not observed but soil moisture was higher in winter months, which may have buffered any temperature shifts. Following both the S09 and W10 burns, a significant treatment*time interaction (p<0.0001 and p=0.0018, respectively) was observed for CO2 flux measurements: S09 burn had a spike in CO2 flux 30-min post-burn whereas in W10, the CO2 spike was smaller and later (24-hr post-burning). Our results suggest that burning shortgrass-dominated southern Great Plains vegetation has little impact on soil chemical properties or CO2 fluxes.