Nutrient and microbial loss in relation to timing of rainfall following surface application of dairy farm manure slurries to pasture

Abstract

This study investigated nutrient and faecal microbe (Escherichia coli) loss in surface runoff following application of dairy manure slurry to intact soil monoliths. Time between manure slurry application and first simulated rainfall event varied from 0 to 20 days. Manure slurries of varying dry matter (DM) content, ranging from 3 to 14%, were also investigated. Results indicated that phosphorus (P), nitrogen (N) and E. coli concentrations decreased with time since application because of chemical and physical breakdown of the manure. Greatest risk to water quality occurred when rainfall was received within 2 days of manure slurry application. When the period between manure slurry application and first rainfall event was ≥10 days, concentrations of N, P and faecal microbes was generally similar to those from dairy grazed pasture. Variation in slurry DM content appears to have little effect on measured runoff concentrations. Results suggest that manure slurries should be applied ≥2 days before rainfall events likely to cause surface runoff in order to limit nutrient and faecal microbe loss when applying manure slurries.