Influence of soil treading on sediment and phosphorus losses in overland flow

This study investigated the effect of simulated cattle treading on soil infiltration rate ( saturated hydraulic conductivity: K-sat) and macroporosity, and the consequent loss of sediment and phosphorus ( P) via overland flow from a grassland and cultivated soil used for dairy farming in southern New Zealand. Treading decreased soil macroporosity and K-sat, and hence time to ponding, which increased the volume of overland flow. Mean suspended sediment concentration was greater in the cultivated treatments ( 0.076 g/ L) compared with the grassland treatments ( 0.014 g/ L). In the grassland soil, sediment and particulate P fractions in overland flow increased with treading due to increased soil disturbance and decreased protection from erosion by grass cover. In contrast, for the cultivated soil, sediment and P concentration and load decreased with increasing treading, due to greater ponding which decreased the erosive power of raindrop impact. Dissolved and particulate P fractions followed similar trends, although mean total P ( mostly particulate P) was greater in cultivated treatments ( 1.07 mg/ L) than the grassland treatments ( 0.64 mg/ L). Relationships were generated between macroporosity and the loss of sediment and P, showing the wider application of macroporosity for environmental assessment than solely an agronomic measurement.