Indispensable Measuring Techniques for Water Relations of Plants and Soils: A Review

Water is essential for the existence of all living forms on the earth, and the kinds and amounts of vegetation occurring on various parts of the earth’s surface depend more on the quantity of water available than on any other single environmental factor. Therefore, the need for the non-subjective, diagnostic assessment tools for water status measurements of plants and soils is indispensable to avoid water shortage problems and achieve sustainable development goals (SDGs) of agricultural sector. The best measure of the energy status of water in plants and soils is the water potential (Ψw), which has the advantage of being physically defined and the force that causes water movement. There are many different instruments that have essential roles for measuring water status of plant, for example, Pressure Chamber, Isopiestic Psychrometer, Pressure Probe, and Osmometers. Each had the ability to indicate not only the water status of various parts of plants and soils but also the forces used to move water from place to place. Nowadays, speaking plant approach (SPA) identifies the optimal crop cultivation conditions based on the physiological status of the plants. The physiological status information from a living plant can be achieved by using a chlorophyll fluorescence imaging robot, which is a powerful tool for early detection of drought stress in plants under practical production greenhouse conditions. Moreover, recently thermal imaging and remote sensing technology are both feasible for precise irrigation guidance and precision water management.