This review has briefly considered the current state of the art and potential opportunities for use of plant-based stress sensing as the basis for irrigation scheduling and control. The advantages and disadvantages of each of these approaches are summarized in Table 1. Although plant-based sensing has several potential advantages, including a greater relevance to plant functioning than soil-based measures, these have been offset by a number of practical difficulties of implementation that have thus far limited the development of commercially successful systems. However, pressures for enhanced water use efficiency and for greater precision in irrigation systems are likely to provide a real impetus for the development of new precision irrigation scheduling systems that take account of the irrigation need of individual plants, and may well involve greater use of plant-based sensing systems.
The author is grateful to sponsors of various aspects of the work presented, who include the European Commission (projects: WATERUSE, contract EVKI-2000–22061, and STRESSIMAGING, Contract HPRN-CT-2002–00254).