The objective of this study was to evaluate the effects of moderate defoliation and grass species on soil nitrogen (N) mineralization in a semiarid grassland of northeastern Patagonia, Argentina. Studied species were Poa ligularis and Nassella tenuis (desirable/preferred by cattle) and Amelichloa ambigua (undesirable/non preferred). Two defoliations were made to a 5 cm stubble height during the growing season. Hypotheses were that (1) net N mineralization and N availability in the soil are increased by a moderate defoliation and greater species forage quality, and (2) potential N mineralization is higher in the soil beneath the desirable than undesirable species. In 2013 and 2014, in situ net N mineralization was estimated using the tube incubation technique under field conditions. Potential N mineralization was estimated by long-term laboratory incubations. Defoliation treatments did not affect the soil inorganic N dynamics. The soil under A. ambigua showed a greater in situ net N mineralization than other species, but only in 2013. Poa ligularis presented the highest initial inorganic N and potentially mineralizable N values. However, the opposite was recorded in this specie for the mineralization constant rate. These results demonstrated that moderate defoliations did not affect soil N availability, and presence of the desirable perennial grasses increased the potential N mineralization pool. Sustainable management practices that promote the persistence of these species in plant community are important to maintain soil fertility on semiarid grasslands.

本研究的目的是评估适度落叶和草种对阿根廷巴塔哥尼亚东北部半干旱草原土壤氮 (N) 矿化的影响。研究的物种是Poa ligularis和Nassella tenuis（牛喜欢/喜欢）和Amelichloa ambigua（不受欢迎/不受欢迎）。在生长季节进行两次落叶，留茬高度为 5 厘米。假设是 (1) 土壤中的净 N 矿化和 N 可用性因适度的落叶和更高的物种草料质量而增加，以及 (2) 理想物种下土壤中的潜在 N 矿化高于不期望物种。2013 年和 2014 年，在野外条件下使用管培养技术估计了原位净 N 矿化。潜在的 N 矿化是通过长期实验室孵化来估计的。落叶处理不影响土壤无机氮动态。A. ambigua下的土壤显示出比其他物种更大的原位净 N 矿化，但仅限于 2013 年。Poa ligularis呈现最高的初始无机 N 和潜在的可矿化 N 值。然而，在该物种中记录的矿化恒定速率相反。这些结果表明，适度的落叶不会影响土壤 N 的有效性，并且理想的多年生草的存在增加了潜在的 N 矿化库。促进这些物种在植物群落中的持久性的可持续管理实践对于保持半干旱草原的土壤肥力很重要。