Abstract
Continued phosphorus (P) inputs are necessary to sustain grassland productivity. Struvite, a sparingly water-soluble P mineral recovered from wastewater, has emerged as an alternative to conventional fertilizers such as water-soluble single superphosphate (SSP). A two-year field study was carried out to investigate the immediate and residual agronomic effectiveness of struvite and SSP in a perennial ryegrass pasture ( Lolium perenne L.). Phosphorus was applied at 20 and 80 kg P ha −1 , alongside unfertilized controls. In Year 1, P addition significantly increased ryegrass dry matter yield by 49% compared with controls. Yields were similar for struvite and SSP at both application rates, although P uptake was significantly higher for struvite (63.4 kg P ha −1 ) compared with SSP (50.9 kg P ha −1 ) at the high P rate. In Year 2, the 80 kg P ha −1 struvite treatment maintained significantly higher yield (23.5 Mg ha −1 ) and P uptake (63.4 kg ha −1 ) compared with SSP (17.4 Mg ha −1 and 50.9 kg P ha −1 ). Soil analyses revealed that concentrations of plant-available P were consistently higher for struvite compared with SSP. The findings of this study demonstrated that the immediate agronomic performance of struvite was equivalent to SSP for low P input, while the immediate and residual effectiveness of struvite at the higher rate of input was superior to SSP. Further research is warranted to determine the relative agronomic effectiveness of struvite for temperate grassland on other soil types under different environmental conditions, together with investigation of the mechanisms responsible for the enhanced plant availability of struvite-P.