Warm-Season Pasture Species Respond to Subsurface Placement of Phosphorus Fertiliser

Abstract

The root traits of many warm-season pasture species have not been characterised thoroughly. Depending on the nature of legume root architecture, alternative phosphorus (P) application strategies may improve the success of legume establishment and persistence, particularly if legumes exhibit a spatially responsive root system. The purpose of the present experiment was to investigate the root morphology of several warm-season pasture species and to determine the response of these species to a subsurface application of P fertiliser. Monocultures of two grasses (Panicum coloratum and Digitaria eriantha) and two legumes (Medicago sativa and Desmanthus spp.) were established in pots to investigate root morphology and P acquisition in response to three soil-P distribution treatments. The P fertiliser that was applied to the subsurface ‘band’ layer was labelled with 32P-radioisotope to determine P recovery. There were significant differences in shoot yield and root morphology among the species. The largest shoot yields were usually produced by plants grown in the uniform high-P treatment, while the grasses generally produced longer roots more efficiently than the legumes across the three soil-P distribution treatments. Nevertheless, each species responded to the banded high-P treatment by acquiring more P from the zone of P enrichment (banded high-P = 31% cf., uniform low-P = 3%, and uniform high-P = 9%). This result suggests that a subsurface application of P fertiliser at the planting stage will benefit warm-season pasture species, particularly grasses that are highly responsive to fertiliser placement. Nevertheless, preferential placement of fertiliser below legumes may improve the productivity of this component if their root systems have more time to respond spatially.