The use of alum to decrease phosphorus loss from dairy farm laneways in southern New Zealand

Dairy farm laneways are sources of enriched P loss. Aluminium sulphate (alum) has been shown to decrease P loss when applied to land; our hypothesis was that alum may serve as a cost‐effective strategy to mitigate P loss from laneways connected to streams. A 4‐month field study, over the milking period when cows regularly used the laneway, showed that alum (25 and 50 kg/Al/ha) initially lowered FRP losses for four events, over 60 days, following application. If connected to a stream, the cost‐effectiveness of alum use on dairy farm laneways (51–75 USD per kg P retained) was high compared to other strategies on a grazed dairy farm.