Impact of Fire on Soil Nutrients in Central Semiarid Argentina.

The modification of the soil chemical properties by fire is directly related to the degree of soil heating and to the weight and spatial distribution of vegetation and litter accumulated. This research was aimed at studying the immediate effects of two controlled burns on the organic carbon (OC), and on the total and available nitrogen (N), phosphorus (P), and sulfur (S) of surface soils (0-5cm) of the southern Caldenal region, Argentina. The pH, CEC, and available cations were also evaluated. Follow-up samplings were carried out yearly, during the three years between the burns. The initial unburned shrub vegetation-covered soil had a greater concentration of total and available nutrients than the herbaceous-covered soil. Soil pH and CEC values were slightly lower in shrub soil. The first controlled burn generally caused a beneficial effect on the total elements either immediately or one or two years after the burn. It also caused a considerable flush of the available nutrients that was more persistent under the shrubs. The changes were temporary and generally, the nutrients levels returned to those of the unburned soils during the second or third year after the burn. On the other hand, a second moderate controlled fire experienced three years later was shown to have no measurable effect on most soil properties, but a decrease of total S in grass soil and NO[sub 3][sup -]-N in woody soil was observed after burning, pointing out the risk of a soil fertility depletion. Consequently, further studies in the Caldenal region are needed to evaluate changes in the soils under circumstances of different fire frequencies. [ABSTRACT FROM AUTHOR]