Precision irrigation for grapevines (Vitis vinifera L.) under RDI and PRD

Water is a scarce resource worldwide and a particular problem for producers of wine grapes in Australia and Chile where periodic drought severely limits vine growth. Most vineyards in these countries are irrigated and the development of efficient water management practices for vineyards is required. Strategies such as regulated deficit irrigation (RDI) and partial root zone drying (PRD) have been introduced with the objective of maximising the efficiency of water use relative to yield while ensuring that grape quality is not compromised. The problem is that the advantages of these strategies can only be realised if there is accurate information about weather parameters, spatial distribution of soil moisture and vine water use and status. This information can then be used to provide answers for growers to the key irrigation questions of when to irrigate and how much water to apply. The overarching hypothesis of this thesis was than an integrated approach to irrigation scheduling incorporating data on weather, physiological status of the vines and soil wetting patterns is essential to accurately target the narrow range of soil moisture and vine stress thresholds required for realising the advantages of RDI and PRD. The hypothesis was tested through a series of field experiments. The results supported that an integrated approach to irrigation produces the most desirable outcomes in terms of water use and berry quality irrespective of irrigation strategies. The most appropriate way to answer the question of when to irrigate is to measure stem rather than leaf water potential. The question of how much water to apply can readily be answered using a new technique and software developed in this study. It was concluded that PRD is more difficult to manage than RDI because of the complexity pf PRD and the financial and logistic requirements of a double irrigation line. PRD had no effect on crop water use efficiency, berry quality or yield when the same amount of water was applied in the PRD and conventional drip treatments