Regenerative management and fertiliser regime impacts on phosphorus cycling in a temperate grazed pasture

Phosphorus (P) cycling underpins productivity and fertiliser use efficiency in grazed pasture systems. However, the effects of regenerative practices such as enhancing pasture diversity and alternative grazing management remain poorly quantified. We investigated regenerative and conventional system effects on soil-plant-animal P dynamics in a three–year dryland grazed experiment. The regenerative system comprised a 12-species diverse pasture mix with short grazing periods and extended recovery, while the conventional system used best-practice grazing of Medicago sativa L. Both systems also included high and low P fertiliser treatments. Plant-available and biological soil P pools, acid phosphatase activity, herbage P concentrations, animal P intake and dung P returns were quantified. The P fertiliser treatments resulted in contrasting soil labile P pools, but management type had no effect. Soil microbial biomass P was greater under high compared to low fertiliser by the final sampling in Year 3 (24.4 vs. 15.8 mg P kg –1 , P = 0.001). Averaged across P fertiliser treatments, soil acid phosphatase activity was 21% higher under regenerative management at the final soil sampling ( P = 0.01). Herbage P concentrations ranged from 1.4 to 4.4 g P kgDM –1 and were strongly correlated with soil moisture (R 2 = 0.50–0.65). Animal P intake was 8.1 kg P ha –1 higher in the conventional in Year 1 only. Dung P returns shifted from higher in the conventional system in Year 1 (+ 7 kg P ha –1 ; P < 0.001) to higher returns in the regenerative system in Year 3 (+ 3 kg P ha –1 ; P = 0.03). These results indicated that three years provided sufficient time for regenerative grazing management to begin measurably shifting P cycling processes, specifically in terms of P mineralisation by acid phosphatase activity and P returns via dung. However, bulk soil P fertility pools remained governed by fertiliser history rather than management type.