Drought, grazing, and nitrogen input influence nutrient supply and soil faunal activity in a semi-arid savannah grassland

Abstract

Dryland grasslands cover approximately 16% of Earth’s land surface and support the livelihoods of people worldwide. However, the mechanisms driving their nutrient dynamics under changing environmental conditions remain poorly understood. This study, conducted in a dry savanna ecosystem in South Africa, investigated how grassland management interacted with drought and nitrogen addition in their effects on soil faunal activity and plant-available macro- and micronutrients. Extreme drought did not significantly affect soil invertebrates’ feeding activity in the top 8 cm, likely due to consistently dry conditions during the experimental period. In contrast, moderate grazing stimulated soil fauna feeding activity in the topsoil. Both nitrogen addition and grazing increased faunal activity, particularly at 7–8 cm depth. Drought conditions were associated with higher concentrations of manganese, zinc, and sulphur, while ambient rainfall conditions resulted in higher total nitrogen, magnesium, iron, and copper. Nitrogen addition enhanced mineral nitrogen availability and led to a fivefold increase in iron, and manganese, and doubling of copper. These findings suggest that moderate grazing management improves soil health in savanna grasslands, even under challenging climatic conditions.