IMPACT OF CATTLE TREADING ON HILL LAND 2 - SOIL PHYSICAL-PROPERTIES AND CONTAMINANT RUNOFF

A simulated rainfall study carried out as part of a larger grazing exp eriment was conducted to investigate the effects of a 2-3 day cattle-t reading event in winter on soil physical properties and contaminant (s ediment and nutrient) runoff in topographically variable hill land. Me asurements were made on two land zones: easy contoured ridges and gull ies (15-24 degrees slope) and steep inter-track land (28-39 degrees sl ope). Simulated rainfall was applied to 16 plots (0.5 m(2)) with a ran ge of treading damage for each land zone within 14 days of the treadin g event. Simulated rainfall was repeated on the same plots in the foll owing summer and winter to assess the recovery of soil from treading d amage. Treading damage reduced water infiltration rate, particularly i n the steep zone. It also caused a significant increase in the transpo rt of suspended solids (SS), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) from the plots during simulated runoff. On the steep i nter-track zone, damaged areas had a 46% lower infiltration rate, and runoff from these areas contained on average 87% more sediment, and 89 % more N and 94% more P compared with undamaged areas. These effects h ad disappeared six months later. The rainfall simulation and soil phys ical studies show that a 2-3 day winter treading event may increase so il bulk density, reduce soil macroporosity and total porosity, and lea d to a decrease in the water infiltration rate and an increase in cont aminant runoff.