Plant-based Irrigation Scheduling
Even under wet soil conditions, plants must match the water demand of their environment with the ability of their roots to take up water from the soil. Plants use many different responses to keep their water supply and demand in balance, and most plant-based methods for irrigation management are based on the measurement of one or more of these responses. The pressure chamber method, for measuring the tension of water within the plant, has been shown to be a reliable physiological measure of water stress in trees, vines, and some field crops, but many other plant-based methods have been proposed in the past, and new ones are being proposed almost as fast as new technologies are developed. One advantage of a good plant-based method is that it can be used to check whether plants are responding favorably to other weather- or soil-based methods of irrigation scheduling. The weather-based methods tell you how much water a non-stressed plant should be using, and the soil-based methods tell you how much irrigation is required to recharge your soil reservoir, but neither tells you when to irrigate. In order to determine when to irrigate using these methods, a number of assumptions must be made regarding the available soil moisture and the root zone depth of your field, and plant-based measurements can indicate whether or not these assumptions are accurate. Plant-based methods are very complimentary to weather- and soil-based methods: plant-based methods indicate when to irrigate but not how much, and weather- and soil-based methods indicate how much to irrigate but not when.
Two approaches to plant-based irrigation scheduling are: