Pastures and drought: a review of processes and implications for nitrogen and phosphorus cycling in grassland systems

The incidence and extent of drought is predicted to increase and therefore understanding the effects on the plant–soil system is important. The objective of this review is to report on the fundamental processes involved in the effects of drought on pasture, soil, and soil microorganisms in grassland systems and evaluate the consequences of drought to determine whether management decisions could mitigate the impact of drought. There are associations within the plant–soil system affecting the flows and cycling of nutrients. Drought conditions often create a flush of nitrogen, carbon, and phosphorus upon rewetting that is at risk of loss to the environment. Prediction of the flush magnitude is difficult because it is influenced by drought characteristics such as duration, soil temperature, degree of drying, and rate at which the rewetting occurs post-drought. Response to drought is also affected by the microbial community population and structure of the soil-related flora and fauna. Increasing pasture diversity and soil organic matter may help to mitigate the effects of drought in grassland systems. More research is needed that incorporates all the components of the plant–soil system to examine the net effects of drought on grassland systems. Better measures are also needed to estimate the consequences for future climate change on nutrient stocks and flows.