Water use and pasture growth on Judgeford silt loam

Abstract

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.

Keywords:

• perennial ryegrass
• evapotranspiration
• soil water balance
• topsoil removal
• yellow-brown earth