Soil Water Repellency - Cost to Precision Irrigated Apple Productivity.

Water repellent (WR) soils are documented to impact a range of hydrological properties, yet studies evaluating the consequences of WR on crop yield and quality are conspicuously absent.  With global concerns on drought and water availability and the projected impacts of climate change, development of novel strategies to optimize efficient rootzone delivery of water are required.  Co-formulations of alkyl polyglycoside and ethylene oxide-propylene oxide (EO/PO) block copolymer surfactants have been shown to improve wetting synergistically.  It is the objective of this study to utilize surfactant treatment to increase soil water content and wetting front depth in a precision irrigated, WR Goulburn clay loam soil in Victoria, AU as a means of estimating potential crop losses to WR in Malus domestica Borkh. (variety “Pink Lady” in 2006/07 and variety “Gala” in 2007/08).   Surfactant was applied at initial rates of 0, 5 and 10 kg ha^-1 in the spring, then at 0, 2.5 and 5 kg ha^-1 respectively monthly for up to four months.  Irrigation practices were identical in each treatment.  As surfactant rate increased, wetting front depth and soil volumetric water increased for each of the surfactant treatments (p=0.05).  Total yield (kg tree^-1) differed significantly between the untreated WR and surfactant treated plots (p=0.05), however, yields between the two surfactant treatment rates were statistically equivalent.   The yield component most affected by WR was mean fruit size - a difference of  0.017 kg in the variety “Pink Lady” and 0.041 kg in the variety “Gala” (p=0.05).   When examining the yield differences on a hectare basis, yield depressions of 3700 – 6000 kg ha^-1 solely attributable to WR were encountered in the two varieties tested.  This study is the first to provide an insight on potential crop losses in apples growing in a WR soil.