(Penn et al., 2012). However, McDowell and Nash (2012) also noted
that as scale and complexity of flow-paths increased the cost effectiveness
of strategies to mitigate P loss decreased. Strategies
that aim to decrease P loss most cost-effectively focus on
decreasing the availability of P at source; for example, by
decreasing soil Olsen P concentration (McDowell and Nash, 2012).
In many soils, especially those used for intensive pastoral
grazing, maintaining soil Olsen P as low as agronomically possible
may still lead to substantial P loss via subsurface flow due to poor P
sorption capacity and continual inputs from excretal returns
(McDowell and Nash, 2012). One amendment, aluminium sulphate
(alum) has been used to decrease the potential for P loss in surface
runoff (e.g. McDowell and Norris, 2014). Alum was therefore tested
to determine if it could also be used to cost-effectively decrease P
loss in subsurface flow from a grazed pasture.