Nutrient, Sediment, and Bacterial Losses in Overland Flow from Pasture and Cropping Soils Following Cattle Dung Deposition

Abstract

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 (1×10⁵ 100 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.