Water use and pasture growth on Judgeford silt loam

Water extraction from a friable silt loam under pasture was measured over summer in 1982–83. The soil had a layer at about 0.5 m which was not readily penetrated by pasture roots. Nevertheless, neutron probe measurements showed that, when the soil water deficits were greater than about 90 mm, water was extracted to a depth of 1.4 m. At a deficit of about 120 mm, over 50% of the water was extracted from the top 0.2 m of soil. Leaf extension measurements showed that ryegrass growth decreased at a deficit of about 50 mm and virtually ceased when the deficit was about 140 mm. The leaf growth recommenced rapidly following significant autumn rain. Evapotranspiration was weather‐controlled when the soil water deficit was less than about 85 mm, and became controlled by soil water at greater deficits. Plots which had topsoil removed 5 years earlier showed similar patterns of water extraction compared to the control plot.