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

Dairy farm laneways are critical source areas of enriched P loss. Aluminium sulphate (alum) has been shown to decrease P loss when applied to land; our hypothesis was that alum may decrease P loss when applied to laneways and do so much more cost-effectively than other mitigation strategies. A four month field study, over the milking period when cows regularly used the laneway, showed that alum (25 and 50 kg Al ha-1) initially lowered FRP losses for four events (60 days) following application. The cost-effectiveness of the use of alum on dairy farm laneways (51-75 USD per kg P retained ha-1) was 3 - 12.5 times better than if used on grazed dairy pastures and therefore may represent better value if runoff from a laneway is connected to surface waters.