Shallow mechanical loosening of a soil under dairy cattle grazing: Effects on soil and pasture

Shallow mechanical loosening of soil to 22 cm deep (aeration) was investigated as a method for ameliorating soil compaction caused by dairy cattle treading. Soil physical and pasture measurements taken over 46 weeks compared plots grazed under normal grazing practice (non-aerated) with plots under normal grazing practice where soil was mechanically loosened (aerated). Aerated soil initially showed reduced (P < 0.05) penetration resistance, degree of packing, and bulk density, and increased (P < 0.05) hydraulic conductivity, total porosity, macroporosity, and proportion of small aggregates, compared with non-aerated soil. However, after 40 weeks aerated soil showed some reversion back to a non-aerated state, and only the most sensitive measurements (penetration resistance, degree of packing, soil structure, and macroporosity) showed significant (P < 0.05) treatment differences. Pasture herbage yield, botanical composition, and root length were unaffected (P < 0.05) by aeration, but aeration increased (P < 0.05) root dry weight and decreased bare ground. This work suggests that timing of aeration with regard to soil moisture and atmospheric conditions is vital for optimal soil and pasture responses. The need to use methods which sample large volumes of soil and pasture to detect soil physical and pasture changes due to loosening is also stressed.