Effects of cattle treading on physical properties of three soils used for dairy farming in the Waikato, North Island, New Zealand

Abstract

A study of the physical condition of 3 soils used for intensive dairy farming in the Waikato Region was undertaken. The study was to determine the existing physical condition of the soil, the possible long-term changes from pugging damage, and the most appropriate measurements and depth for monitoring change in soil physical properties under dairying.

Four dairy farms were selected on each of 3 soils (an Allophanic Soil and 2 Gley Soils). On each farm, 3 sites that corresponded to never trodden, usual (‘average’ paddock and pasture condition for the farm), and previously pugged (pugged >18 months ago) pasture histories were sampled. Undisturbed soil cores were collected at 50-mm depth increments to 250 mm for determination of bulk density, total porosity, saturated and unsaturated hydraulic conductivity, proportion of pores >30 and 60 µm, and aggregate size class.

Results showed pugging was having a long-term effect on soil physical properties of all 3 soils, including the well-drained Allophanic Soil that rarely pugged. All measurements showed a decline in values for soil properties from never trodden to previously pugged. The greatest changes were in hydraulic conductivity, proportion of pores, and aggregate size (>60 and <20 mm).

The most appropriate depth increment for measuring differences between treatments was found to be 50–100 mm. A comparison of previously pugged to never trodden at this depth showed that hydraulic conductivity had decreased by 80%, pore size by 46% (except for Allophanic Soil), and the proportion of aggregates >60 mm in diameter had increased at least 4-fold.

Farming practices that minimise pugging damage, such as on/off grazing, need to be encouraged. It is possible that such programs may permit the soil to recover to a physical state similar to never trodden sites.