The Effects of Dairy Cow Live-Weight and Stocking-Density on the Physical Properties of a Poorly Drained Soil.

The objectives of the current study were to investigate the effects of dairy-cow live-weight and stocking-density, on soil physical properties and surface damage in the upper layers of a clay-loam textured soil (Solohead, Tipperary, South Ireland) under rotational grazing.  Two dairy-cow breeds were compared, Holstein-Friesian with a mean live-weight of 570 kg and Jersey cross Holstein-Friesian with a mean live weight of 499 kg. Both breeds were split into two herds and a low and high stocking-density was imposed. The grazing area was divided into six blocks, each having four paddocks, one of which was assigned to each grazing system. Soil physical properties (soil bulk density, total porosity, macroporosity, gravimetric moisture content, volumetric moisture content, air-filled porosity, penetration resistance, shear strength and poaching damage) data were collected throughout 2011 and 2012. These years provided contrasting weather conditions with much higher rainfall recorded in the main grazing season, March to October inclusive, in 2012 when compared to 2011 (784 versus 588 mm).  Hoof size was measured for a subset of cows (20 per breed) in order to establish the surface loading pressure imposed on the soil by both breeds during grazing. In spite of a significant difference in live-weight between the breeds it was found that the surface loading pressure was the same regardless of breed, due to a direct correlation between live-weight and hoof-size. Soil physical properties were not affected by dairy cow live-weight, with the exception of poaching depth which was significantly higher in the Holstein-Friesian treatment paddocks (38.7 versus 36.7 mm). Stocking density significantly affected poaching damage with higher levels in the high stocking density treatments. The soils behaviour was more influenced by its moisture content than by the treatments imposed and as a result, all herds had an adverse affect on soil function during 2012.