Sodium chloride and soil texture interactions in irrigated field grown sultana grapevines. 3. Soil and root system effects

Five salinity treatments, ranging between 0.37 and 3.47 dS m-1, were applied through a trickle irrigation system to own-rooted sultana grapevines for six years. The changes in soil salinity levels and the relationship between soil salinity and yield were studied, and a simplified salt balance model was developed to calculate leaching fractions. Soil salinity was strongly influenced by soil texture as well as by salt treatment, because leaching fractions were lower in heavier soils; they averaged 23% in the lightest soils and 10% in the heaviest. Leaching fractions also increased with salt treatment, from 7% in the 0.37 dS m-1 treatment to 24% in the 3.47 dS m-1 treatment. This was probably because water use by salinized vines was lower. Yield was correlated with mean soil salinity, ECe, but the relationship was not as good as with plant salinity levels. The fitted model accounted for between 52 and 62% of the variance. It was concluded that soil salinity levels at the end of winter should be maintained below 1.0 dS m-1 in order to keep yield losses below 10%. For own-rooted sultana grapevines in Sunraysia, this requires a leaching fraction of about 8%. Rootzone depth and root density were lower in the heavier soils, and were decreased by salt treatment. The deleterious effects of salt treatment on clay dispersion and soil hydraulic conductivity were also greater in the heavier soils. Soil properties must therefore be considered when predicting the effects of saline water on crop productivity, especially in the long term.