The use of alum to decrease phosphorus losses in runoff from grassland soils
journal contribution
posted on 2023-05-03, 11:48authored byRichard McDowell, Matthew Norris
Phosphorus (P) loss from land can impair surface water quality. Aluminium sulphate (alum) treatment of manure or slurry has been shown to decrease P loss when waste is applied to land; our hypothesis was that alum may also decrease P loss when directly applied to grassland grazed by dairy cows. A rainfall simulation generated runoff from five soils 2, 4, 7, 14, 38 and 118 d after they were treated with or without dung and alum (0, 20, 40 and 80 kg Al ha-1). For soils with and without dung applied, alum decreased mean concentrations of filterable reactive P (FRP) by 25-70% and total P (TP) by 20-40%, depending on soil P, Al and Fe concentration and alum application rate. An equation (R2 = 0.98) was generated to predict how long after application the effect would be significant. A 14 month field trial compared runoff P losses from plots that received 25 and 50 kg Al ha-1 applied within a week of grazing by dairy cattle in spring (4 months after the trial started). Alum application decreased runoff-weighted concentrations (and loads) of FRP by 47-52% and TP by 25-34%. At 157-944 $ kg-1 P mitigated, cost-effectiveness was estimated as medium compared to exiting strategies for mitigating P loss in dairy farms. Cost-effectiveness would be improved by the spatial and temporal targeting of alum application to areas of a farm or catchment that lose the most P.
McDowell, R.W., & Norris, M. (2014). The use of alum to decrease phosphorus losses in runoff from grassland soils. Journal of Environmental Quality, 43, 1635-1643