Mitigation of Soil Water Repellency Improves Rootzone Water Status and Yield in Precision Irrigated Grapes.

Millions of hectares of Australian agricultural lands are impacted by soil water repellency (SWR) which reduces infiltration capacity and seed germination, and increases erosion and leaching of pesticides and fertilizers.  However, research on crop yield is limited to a handful of crops – barley, lupin, and potatoes. Drip irrigation is extensively employed in horticultural crops to improve water use efficiency in water scarce environments, yet the consequences of SWR on soil water and crop productivity are conspicuously absent.  The objective of this study was to utilize surfactant treatments to mitigate SWR in clay loam or loam soils under drip irrigation and to assess soil water status, and potential crop losses in grapes (Vitis vinifera L.).  Three replicated trials were conducted in Victoria, AU on table grapes (‘Black Muscat’) or wine grapes (‘Shiraz’) growing.  ACA 1848 (a blend of alkylpolyglycoside and block copolymer surfactants) was applied at initial rates of 0 or 5 L ha^-1 in the spring, then at 0 or 2.5 L ha^-1 monthly for up to four months.  Soil volumetric water content (VWC) was monitored at 10 cm or 25 cm using a Theta probe (Delta-T Devices, Cambridge, UK).  At harvest, fruit weights were measured and used for crop yield estimations.  VWC was consistently lower (p = 0.05) in untreated soils than in the surfactant treatments regardless of soil type.  Bunch weights were significantly lower and heat stress damage higher in the untreated controls (p = 0.05).  SWR induced yield differences of 2.4–2.5 Mg ha^-1 (13%) were observed between the two treatments (p = 0.05) and resulted in a net difference in financial return of $2053 - $4922 ha^-1.  This study demonstrates that SWR depresses grape productivity and that simple SWR mitigation strategies can have profound effects on soil hydrological status to improve sustainable grape production.