Pasture plants and soil fertility management to improve the efficiency of phosphorus fertiliser use in temperate grassland systems

Abstract

Phosphorus (P) fertilisers are important for productivity in many grassland systems. Phosphorus is a non-renewable and finite resource, and there are environmental and economic reasons for using P more effectively. We review the P balance of temperate pastures to identify the factors contributing to inefficient use of P fertiliser and discuss ways to improve P-balance efficiency. Immediate gains can be made by ensuring that P fertiliser inputs are managed to ensure that the plant-available P concentrations of soil do not exceed the minimum concentration associated with maximum pasture production. Unnecessarily high soil P concentrations are associated with greater potential for P loss to the wider environment, and with higher rates of P accumulation in soils that have a high P-sorption capacity. Soil microorganisms already play a crucial role in P cycling and its availability for pasture growth, but are not amenable to management. Consequently, plants with lower critical P requirements, particularly because of better root foraging, will be an important avenue for improving the P-balance efficiency of fertilised pastures. Traits such as long fine roots, branching, root hairs, and mycorrhizal associations all contribute to improved root foraging by pasture plants; some of these traits are amenable to breeding. However, progress in breeding for improved P efficiency in pasture plants has been minimal. It is likely that traditional plant breeding, augmented by marker-assisted selection and interspecific hybridisation, will be necessary for progress. There are practical limits to the gains that can be made by root foraging alone; therefore, plants that can ‘mine’ sparingly available P in soils by producing organic anions and phosphatases are also needed, as are innovations in fertiliser technology.