Impact of soil phosphate retention capacity on potential phosphorus loss from contrasting fertilisers

Context Recovery and reuse of phosphorus (P) from waste materials in the form of sparingly soluble struvite may improve P use efficiency and reduce adverse environmental impacts associated with diffuse transfer of P from land to water. Aims To compare the immediate P loss by leaching from application of struvite and superphosphate to low and high P-retention grassland soils. Methods The equivalent of 100 kg P ha−1 of struvite and superphosphate was applied to the surface of soil columns, and P loss was determined over seven consecutive weekly leaching events. Key results As expected, application of P significantly increased P loss over seven consecutive leaching events in both soils. The P loss by leaching from the low P-retention soil was approximately 80% higher for superphosphate compared with struvite. The P losses from the high P-retention soil were also higher for superphosphate than struvite, but the differences were not significant. The latter was partly attributed to greater bypass flow in the high P-retention soil (sandy loam) compared with the low P-retention soil (silt loam). Conclusions The findings indicated that struvite has potential to reduce leaching P loss risk compared with water-soluble P, which may also be influenced by a combination of soil P retention capacity and texture. Implications Further studies are needed to evaluate the potential environmental advantages of using struvite under field conditions in grassland systems, and to investigate the physicochemical mechanisms responsible for the reduced mobility of struvite-P in soil.