An experiment was conducted on steep hill land in New Zealand to describe the pattern of cattle treading that occurred from a single damage event during winter. The experiment also measured some of the consequences of treading and sought to define the subsequent grazing management which promoted the most rapid recovery of pasture.In hill paddocks of mixed topography, damage of the soil surface was greatest on animal tracks/ camps and easy contoured areas (<25°) where cattle prefer to walk. Evidence of this initial winter impact disappeared over spring, most rapidly on easy contoured areas and under continuous sheep grazing. To promote rapid recovery of damaged paddocks continued grazing of cattle during spring should be avoided.At high levels of damage (>50% soil surface), puddling on tracks/camps and skid damage on steep inter-tracks became frequent. These processes are significant because animal tracks/camps act as important channels for surface water flow in hill lands; and disturbed, inter-track areas are an important source of sediment runoff.During spring, pasture growth rates were reduced by treading damage. From a systems context this could represent losses of 5-10 kg DM ha -1 d -1 during early-mid spring. Pasture cover and growth rates had fully recovered by early December.

Damage to pasture as a result of intensive grazing and treading by cattle increases the erosion of sediment and associated nutrients. In this study we present a model for the effect of treading damage on interrill erosion. The model formulation is based on the interrill erosion components of conventional process-based erosion models, with some modifications. The model was developed using data from small rainfall simulator plots (0.5 m2) on hill-country pasture in New Zealand with varying amounts of treading damage. Treading increased the amount of bare ground, and this resulted in increased concentrations of sediment in runoff. Concentration was found to increase linearly with the amount of bare ground. Treading resulted in increased runoff, which had some effect on sediment concentration for the high runoff rates in the experiments, but would have a negligible effect on concentration for typical natural runoff rates. However, the increased runoff results in greater sediment loads because a larger volume of sediment-laden runoff is produced. The increase in runoff was modelled through a reduction factor for the hydraulic conductivity which varied linearly with the fraction of damaged ground. For 100% damaged ground the hydraulic conductivity was approximately halved. The recovery of bare ground and damaged ground over time after treading was also assessed. Bare ground resulting from treading typically halved after 2 months, while damage took longer to recover. Such treading-related effects are superimposed on seasonal variations in erodibility, bare ground, and infiltration capacity. Based on the results of the study, some measures to reduce treading-related erosion are suggested.

The effect of sheep grazing on the loss of sediment and nutrients in overland flow was investigated on a hill-country farm in the Waikato, New Zealand. The losses were measured in runoff produced artificially with small (0.5 m2) and large (1050 m2) rainfall simulators. Immediately after intensive winter grazing, rainfall applied at high intensity increased concentrations by a factor of 13–16 for sediment and particulate nutrients, 33–76 for dissolved reactive phosphorus and ammonium-nitrogen, and 5–7 for dissolved organic nitrogen and phosphorus. During summer, when there was less removal of vegetative cover, there was a smaller effect of grazing. The concentrations of sediment and particulate nutrients in overland flow were strongly correlated with the percentage of bare ground. The concentrations returned to background levels within 6 weeks after grazing, and the infiltration rate and ground cover also recovered from grazing in this time. The small rainfall simulator experiments showed that the infiltration rate decreases with grazing, which results in greater runoff after grazing. The greater runoff combines with the increased concentrations to give higher loads after grazing. In late winter, the infiltration rates were approximately half the summer values and the soil erodibility was approximately double, so the risk of high sediment and nutrient loads is greatest in winter, especially considering the higher rainfall and lower grass growth. The management implications are that exposure of bare ground associated with intensive grazing should be avoided, especially in winter.

Abstract:Animal treading can change soil physical properties, and thus is an important factor in hydrological modelling. We investigated the impacts of animal treading on infiltration by using a series of rainfall simulation experiments at Whatawhata Research Center, Waikato, New Zealand. The study identified significant variables for estimating soil steady-state infiltration at a microsite (0Ð5 m 2 ) and fitted the Green and Ampt equation by modifying or including variables for soil and water parameters and animal activities on grazing paddocks. A regression function for estimating steady-state infiltration rate was created for each of four scenarios: between tracks (inter-track), track, easy slope with ash soil, and easy slope with clay soil. Significant variables included the number of days after treading, antecedent soil moisture, field capacity, percentage of bare ground, bulk density, and the high degree of soil damage (damage not compacted). Regression models explained more than 71% of the variance in steady-state infiltration for three scenarios, but only 53% for the easy slope with clay soil. The remodified Green and Ampt equation provided satisfactory estimation of infiltration for all scenarios (accuracy >80%), and thus enables us to use the modified model for Waikato hill country pastures of different topography, soil physical condition, season and grazing management.

Sediment and chemical losses in surface runoff can be significant on land with rolling topography. These effects can be more severe in grazed pasture systems because of animal treading damage to the ground surface. The phenomenon of treading includes soil compaction, pugging, creating tracks and surface cracking. Modelling results presented in the paper provide estimation of changes in water infiltration rate with land of different topography, soil physical condition, season and grazing. These models were derived from field data collected over 3 years and were specified for micro-sites (0.5 m2). The modelling results identified that micro-site infiltration analysis was appropriate to land with complex grazing and topographic conditions. The correlation between the model estimation and field measures was up to 73% (adjusted R2). Keywords: animal treading, infiltration rate, soil compaction, runoff, cellular automata, spatial modelling