Influence of cattle grazing on nitrogen cycling in soils beneath Stipa tenuis, native to central Argentina

Direct effects of herbivores on plants and on the physical environment can accelerate inorganic nitrogen (N) flow in grassland ecosystems. This study compares N content and N mineralization in the soil beneath plants of Stipa tenuis growing in adjacent grazed or ungrazed areas at three sites in central Argentina. Grazed areas had a long history of heavy, year-long grazing by cattle (6–8 ha cattle−1), whereas ungrazed areas had been excluded from grazing by large herbivore for five to ten years. N content and N mineralization was measured in the soil under plants (n = 10 per grazing treatment and per site) of the studied species at monthly intervals along an annual growing cycle. N mineralization was measured both in situ and in laboratory under optimal conditions of moisture and temperature. We did not found a significant effect of grazing on N content or on N mineralization in the soil beneath S. tenuis all over the studied period. Sustained, long-term overgrazing by domestic livestock, through plant and soil deterioration may either counterbalance or override accelerating N cycling attributed to prudent grazing (i.e., grazing that favours plant productivity and persistence) in managed grasslands.