Depletion of soil water from a Tokomaru silt loam by a perennial ryegrass sward

Abstract

An automatic rain-out shelter and an oscillating sprinkler irrigater were used to give contrasting dry and wet soil moisture regimes during summer in a ryegrass sward grown on a Tokomaru silt loam (Fragiaqualf). Measurements of volumetric water content were made about once a week using a neutron probe. These measurements showed that at the maximum water deficit, 39, 28, 20, and 13% of the soil moisture in the top 100 cm were lost from successive 25 cm depths down the soil profile. Soil water deficits, calculated by integrating the soil water contents down to 100 cm, were linearly related to the rate of water loss from the soil, i.e., evapotranspiration. Measured soil water deficits were compared with predicted deficits calculated using previously published soil water balance data. Close agreement was obtained when the appropriate relationship for soil-controlled evapotranspiration was used.

Keywords:

• soil water deficit
• soil water balance
• water stress
• evapotranspiration