ISHS Acta Horticulturae 689: VII International Symposium on Grapevine Physiology and Biotechnology
COUPLING OF PLANT TO SOIL WATER STATUS AT DIFFERENT VINEYARD SITES |
| Authors: | B.R. Gruber, H.R. Schultz |
| Keywords: | water potential, irrigation management, total transpirable soil water, FTSW, soil water content |
| Abstract:
Spatial variability in soil-type and depth and subsequent water holding capacity is very high in many viticultural regions of the world. Thus, water management needs to be site specific and plant available soil water may need to be assessed for each vineyard or even at different locations within a single vineyard. Due to differences in rooting depths and water extraction profiles and their seasonal dynamics, only direct measurements of vine water status provide sufficient information for irrigation management decisions. Whole-plant transpiration rate, predawn leaf - (  PD), and midday leaf (1) and/or stem (stem) water potentials have been proposed as a guide for these decisions, yet the coupling of these water status indicators to soil water status is problematic and usually unknown.
We have used the concept of total transpirable soil water (TTSW) and the fraction thereof (FTSW), originally proposed for herbaceous plants, to evaluate the coupling between soil water availability and plant water status measurements in an irrigation trial at three contrasting vineyard sites across a spatial transect of 20 km.
Soil water holding capacity as a function of rooting depth was 380, 260 and 100 L m-2 while TTSW was 175, 130, and 50 L m-2, respectively, at the three locations.
We found a single common relationship between PD and FTSW for all vineyards, irrespective of water extraction profiles and canopy systems.
This relationship was not affected by hysteresis after intermittent rainfall events.
In contrast, stem basically reflected changes in plant hydraulic conductance as estimated from sap flow data and was largely uncoupled from soil water availability.
The relationship between ΨPD and FTSW is currently being used in a model for irrigation scheduling.
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