Factors influencing cover crop water competition in vineyards and implications for future drought adaptation

Abstract

Vineyard water management in Australia is often associated with irrigation in warm and hot climates, but in cooler regions the larger share of the seasonal water demand is met by rainfall. This study investigated opportunities to improve the utilization of this rainfall derived water. It focussed on factors that influence grapevine root distribution, ground cover water use, and possibilities to improve drought resilience without increasing reliance on irrigation. It was undertaken in the context of growing interest in the use of permanent cover crops, and a need to better understand how the benefits can be balanced against competition for water during seasons of low rainfall.

Field sites were established in spring 2019 in three own-rooted Shiraz vineyards in the Orange wine region differing in floor management practice, ground cover plant species, rainfall, soil type and irrigation use. Soil and plant water dynamics were then followed for four years, spanning the final season of the severe 2017-2019 drought and three subsequent seasons of high rainfall associated with consecutive La Niña events. Water use traits of ground cover species were characterized, including leaf gas exchange measurements and transect soil coring combined with next generation sequencing to map relative species differences in root distribution and depth. After adaption for use with southern hemisphere vineyards, simulations were then run with the HGU water balance model to test how variations in floor management practices, total plant available soil water or the relative grapevine share of plant available soil water, could have changed water risk through droughts in the historical climate record.

The results suggest the capacity to reduce water competition and conserve rainfall derived soil water is much less than appreciated with current vineyard designs and management practices. The greater opportunity to increase drought resilience may be in the design of new vineyards and encouraging greater exploration of the available soil volume by the grapevine root systems in the first seasons after planting. The latter through staged introduction of cover crops, and understanding the interactive effects of rainfall and irrigation on root distribution. This presentation will describe the findings supporting these conclusions, and discuss the potential gains in water use efficiency in relation to expected increases in future water demand and drought severity with climate change.