The timing and amount of irrigation on vines is typically determined by monitoring volumetric soil water content (VWC). This approach has proved useful over many years with the assumption that plant health, growth and yield can be directly correlated with VWC.
While a good intuition will conclude that a healthy vine will grow on soil of adequate moisture, and not flooded or bone dry soil, intuition is not as clever at determining the optimal value of VWC. Therefore we often rely on hazy definitions such as field capacity and refill points to let us know when we should turn the pumps on and off.
Measuring VWC has become so ingrained for many growers and scientists it is often forgotten exactly what is being measured. Increasingly, growers and scientists have come back to the realisation that VWC has vast limitations and measuring the more meaningful parameter of soil water potential is far more important.