Nutrient, sediment, and bacterial losses in overland flow from pasture and cropping soils following cattle dung deposition

The loss of phosphorus (P), suspended sediment (SS), ammonia (NH4+-N), nitrate (NO3--N), and Escherichia coli in overland flow (OF) from dairy cattle dung can impair surface water quality. However, the risk of P and N loss from grazed pastures varies with time. Current practice in southern New Zealand is to select a field, cultivate, sow in Brassica spp ., and graze in winter to save remaining pasture from damage. This deposits dung when soil is wet and OF likely. Hence, we determined P, NH4+-N, NO3--N, and E. coli loss from dung in OF via simulated rainfall from intact grazed pasture and cropland treatments of a soil. Analysis of OF, 0, 1, 4, 11, 24, and 43 days after dung deposition at the upslope end of soil boxes indicated that total P (TP), NH4+-N, and SS concentrations decreased sharply from day zero and leveled out after 11 days. More particulate P and SS were lost from the cultivated than pasture treatment, whereas the reverse occurred for dissolved organic P because of greater sorption of phytase active materials. Escherichia coli losses were high (1x10(5) 100 mL(-1)) in both treatments throughout. Using the equations of fit in an example field site indicated that management of dung deposition could affect up to 25-33% of TP lost in OF.