A series of lysimeter and field experiments, complemented by modeling at the leaf, whole plant, and vineyard scale, are used to understand transpiration losses from grapevines and to determine the onset and impact of water stress. New data are presented to illustrate that direct measurement of sapflow and the use of mechanistic modeling are complementary tools to quantify the degree and timing of water stress. We then model the impacts of water stress on carbon allocation within the vines. Long-term weather data are used to prescribe the probability and amount of irrigation needed so that sustainable and equitable allocation policies are developed for irrigation consents. Our model calculations for the annual water balance of winegrapes growing in New Zealand on Raupara shallow silt loam predict an average annual irrigation requirement is 112.5 mm yr−1. Throughout half the years, the vines will need less than this amount, and more during the the other half of the years. However, there is a 10% risk of failure that the vines will need more than 197.5 mm of irrigation in any 1 yr. Using models that provide predictions at any specified level of security enables growers and regulators to discuss the trade-off between the level of water allocation sought and the probability of failure. Decision support tools based on mechanistic models are valuable for equitably allocating irrigation water for today’s conditions and with resilience for those scenarios that we presume might happen in the future.

Associated Models

References

Green, S.R., B.E. Clothier, C. van den Dijssel, M. Deurer and P. Davidson, 2008. Measurement and modelling the stress response of grapevines to soil-water deficits in their rootzones.  Chapter 15, InSoil Science Society America Monograph“Modeling the response of crops to limited water: Recent advances in understanding and modeling water stress effects on plant growth processes”, L. Ahujaet al.[Eds]  Chapter 12, pp 357-386