Simple versus Diverse Temperate Pastures: Aspects of Soil–Plant–Animal Interrelationships Central to Nitrogen Leaching Losses.

Decoupling productivity and environmental pollution growth is a key objective of modern agricultural systems. The use of diverse (multispecies) pastures may contribute to this objective. Increasing the species diversity of intensively managed pastures can potentially increase annual herbage growth and N use efficiency. Here, we review the literature on simple (predominantly perennial ryegrass and white clover mixes) and diverse temperate pastures (those with three or more sown species) that address the soil-plant-animal interrelationships relevant to N leaching losses from intensive grazing systems. An analysis of trial results suggests that annual herbage yields from diverse mixtures are greater than those from simple mixtures. The review also suggests that greater species diversity in pastures can increase sward N uptake, attributable to complementarity of species through differentiation in rooting depths and seasonal plant growth activity. The presence of specific species in the sward was more relevant to herbage production and N dynamics than the number of species present in the sward, emphasizing the role of well-adapted plant functional types. The inclusion of forbs (e.g., chicory and plantain) in pastures is also shown to aid in reducing the N load of urine patches, thereby reducing the risk of N leaching from grazed pastures. To achieve the objective of increasing productivity and reducing N leaching, research questions remain around the role of species diversity on other aspects of the production system and N cycle, such as soil type and species adaptation, plant N uptake, and management of diverse pastures for successful on-farm implementation. [ABSTRACT FROM AUTHOR]