Subsurface irrigation: a means to reduce chemical and water inputs in vineyards

Abstract

Context and purpose of the study – Grape growers around the world are seeking to reduce their reliance on herbicides. However, traditional alternatives to chemical weed control do not always integrate seamlessly into established vineyard operations. Employing nonchemical weed management often requires trellis alterations, purchasing or hiring new equipment, and depending on region, may significantly increase tractor passes required to reach desired level of weed control. Critical thinking and thoughtful strategies are necessary to minimize expenditures and maintain quality during the transition away from herbicides. In this trial, irrigation was installed underground in an effort to minimize water loss due to evaporation, better direct the water to the vines, and reduce weed growth in the difficult to control undervine area.

Material and methods – Split-plot trials were established, with sections of the vineyard having dripline installed 30 cm below the surface and 30 cm off the vine row, rather than the standard above ground in-row configuration. Trials were carried out in Syrah vineyards in Hawke’s Bay and Sauvignon blanc vineyards in Marlborough, both in New Zealand. Vines received the same irrigation amounts and timing, canopy management, and spray regime as the control, the only difference being the location of the dripline. Five two vine replicates were set up in each treatment for measurements of vine performance, fruit development, juice composition, and productivity. Undervine weed growth was assessed visually as well as by measuring fresh biomass within a 625 cm² quadrat in the vine row at budburst, flowering, veraison, and harvest.

Results – There were no consistent significant differences in canopy development, midday stem water potential, berry growth, juice chemistry, and productivity between vines receiving their water from below ground rather than above. The major consistent difference between treatments was in the amount of weed growth in the challenging undervine area. Once regular irrigation was established in the blocks, there were significant differences in the undervine weed growth between treatments. Irrigation fed weeds in the subsurface treatment grew in the alleyway, where they could be controlled with a normal mowing pass, rather than specialized under vine equipment. Having some blocks with subsurface lines allows growers to irrigate the subsurface blocks during the day and above ground blocks at night, reducing evaporative losses. Industry trials with subsurface irrigation showed that water use could be reduced by 30% with no loss in yield or quality compared with aboveground irrigation. Subsurface irrigation offers a viable way to reduce the need for herbicide sprays, and offers the potential to more efficiently irrigate, thereby reducing both the water and chemical footprints of vineyards.