Groundwater use in forage production: the effect of saline–sodic irrigation and subsequent leaching on soil sodicity

Abstract

Lucerne plots were irrigated with waters of electrical conductivity (EC) = 0.1, 0.8, 2.5, 4.5 and 7.5 dS/m for the summers of 1991–92 to 1994–95. Within those 4 years, soils were sodified at irrigation treatment salinities greater than 0.8 dS/m. Subsequent leaching of salts with channel water (EC = 0.1 dS/m) and rain water (1995–97) reduced surface soil sodicity but not subsoil sodicity. This resulted in increased dispersed clay in the subsoil. Clay dispersion was best explained by exchangeable sodium percentage (ESP) and Mg in topsoils, and by ESP and salinity (TCC or Cl) in subsoils. Ponding of water, following a 46 mm spring rainfall event, increased with ESP of topsoils. Short-term millet yields over the 1996–97 summer were not affected by soil sodicity despite channel water irrigation. However, cumulative pasture yields over 1997 decreased by 25% between high and low levels of residual soil sodicity.