Dairy pasture responses to soil physical properties

Relationships between relative seasonal pasture yields ( total, spring, or summer/ autumn) and soil physical properties were investigated. Dairy farm data were collected from trials over 7 years. There were few significant response relationships between total relative yield and each soil physical property at each soil depth, from 0 to 20 cm. Macroporosity (air-filled porosity; pores > 30 mum), percentage of pores > 300 mum, and total porosity at both 0 - 5 and 5 - 10 cm soil depths all had highly significant positive relationships with spring relative yield, with the best fit being for macroporosity. Summer/autumn relative yield had significant but negative relationships with macroporosity and the percentage of pores > 300 mum at both 0 - 5 and 5 - 10 cm soil depths, and saturated hydraulic conductivity at 0 - 5 cm. Summation of yield data into seasonal totals gave more meaningful relationships with macroporosity, compared with summation over several individual yield harvests within a season. Macroporosity at 0 - 5 and 5 - 10 cm was the most useful indicator for predicting spring and summer/ autumn pasture yields, but none of the physical measurements was a reliable indicator of total yield.