Measurement and modelling of runoff and phosphate movement from seasonally dry hill‐country pastures

Abstract In seasonally dry hill pastures on a Waipawa stony loam (Pallic Soil) in Hawke's Bay, a range of methods was used to measure phosphorus (P) movement and losses in runoff water. Measurements with a rainfall simulator and micro‐plots showed that dissolved reactive P (DRP) and total dissolved P (TDP) concentrations in surface runoff were directly related to soil Olsen P (R2= 0.93 and R2 = 0.90 respectively) status. The distance that surface runoff travelled, as measured by P fertiliser transport, was about 5 m when rainfall in autumn had not occurred for 12–22 days, but decreased sharply in subsequent rainstorms. Over a 12‐month period most natural surface runoff occurred mostly during early summer to late autumn and was inversely related to soil moisture content (R2= ‐0.38 for all data). Most (55–84%) of total P (TP) losses occurred in three of 12 storms measured, with the majority as DRP from low P (60–85%) and high P (70–93%) soils. Continuous flows from twin catchments of 12.6 ha (north, with lo...