Effect of simulated dairy cow treading on soil physical properties and ryegrass pasture yield

The effects of simulated dairy cow treading on soil physical properties and perennial ryegrass pasture yield were studied in the field, on a Wakanui s ilt loam in Canterbury, New Zealand. The study minimised pugging damage com mon wit, h grazing, to investigate effects of treading and soil compaction on yield and soil physical properties. Pasture yield was decreased by up to 14% for individual harvests, while the total yield for all harvests was de creased by 9%, for the heavily treaded treatments. Treading reduced macropo rosity (the volumetric percentage of pores > 30 mum diameter) at 0-5 cm, in summer, from 20.5% (v/v) in the control to 10.7% in the heavily treaded tr eatments. In winter, macroporosity at 10-15 cm was reduced from 8.5% in the control to 6.1% in the heavily treaded treatments. Similar trends for bulk density, penetration resistance, and air permeability are presented. Tread ing also increased root length by 36% compared with the control. A quadrati c relationship between macroporosity and pasture yield indicated that at 5% and 10% macroporosity, yield was 75% and 88% of maximum, respectively. Opt imum macroporosity was 16-17%, while a critical macroporosity was 9-11%. Pe netration resistance associated with 9% macroporosity was 1.4 MPa, while it s optimum was 0.89 MPa.