Evidence for the leaching of dissolved organic phosphorus to depth

Phosphorus (P) can leach fromtopsoil in inorganic and organic forms. While some evidence has shown inorganic P (orthophosphate) can leach to depth in some soils, less is known of dissolved organic P (DOP). This is not helped by a paucity DOP data for groundwater. We hypothesized that DOP species would leach in greater amounts to depth and at a faster rate through aquifer gravels than orthophosphate. We applied superphosphate with or without dung to a low P-sorption soil under pasture and irrigation. Between 0.7 (control) and 2.4 (dung +superphosphate) kg P ha(-1) was leached through 30 cm with a mean ratio of DRP to DOP of 1.5. At 50 cm, 0.7 and 1.3 kg P ha(-1) was leached with the DRP to DOP ratio decreasing to 1.1 due to greater DOP leaching (or DRP sorption). Therewas little difference in DRP lossesmeasured at 50 and 150 cmdepth. All DOP compounds except the monoester - inositol hexakisphosphate were leached at a faster rate than orthophosphate through aquifer gravels. These data suggest that where low P-sorption soils overlay similarly low P-sorption aquifers, DOP may reach groundwater at a faster rate than orthophosphate. Furthermore, as many DOP species are bioavailable to periphyton, our data suggest that DOP should be included in the assessment of the risk of P contamination of groundwater where connection to baseflow could be a long-term stimulant of periphyton growth. (C) 2020 The Authors. Published by Elsevier B.V.

Automated summary

Studies have shown that dissolved organic phosphorus (DOP) may leach to deeper layers at a faster rate than inorganic phosphorus (orthophosphate), particularly through aquifer gravels. Monitoring data indicates that DOP compounds leach faster than orthophosphate, and for low P-sorption soils, DOP may enter groundwater faster than orthophosphate.