Water-saving irrigation systems sometimes need to understand the moisture content in crop plant tissues to achieve high irrigation quality, thereby adjusting the irrigation schedule based on the conditions. So, what are the techniques for detecting plant moisture content? Below, CHENGSA Holdings will explain for everyone.

Water is the most abundant component in growing plants. It is the substance with the highest content in the fresh weight of animals and plants, playing a crucial role in life activities. The growth and development of plants have specific requirements for water content; both excess and deficiency can affect normal physiological and biochemical processes. Detecting plant water content ensures that plants grow and develop in an optimal environment.

The main purpose of detecting water content is to provide guidance for irrigation. Water-saving irrigation systems face two issues in production: first, under conditions of sufficient water sources, there is often excessive frequency and volume of irrigation, leading to waste of water resources; second, under conditions of insufficient water sources, optimal irrigation decisions cannot be made, and water use efficiency cannot be improved.

Before the advent of computer technology, scientists mainly reflected plant water content by detecting indicators related to water content within plants, such as cell sap concentration. The subsequent emergence of computer technology and sensors greatly expanded the measurable range, so indicators that can be directly measured externally, such as canopy temperature, began to be used for detecting plant water content.

The emergence and maturation of current technologies like image processing and remote sensing have further enhanced the scientific nature and accuracy of water detection techniques. Most plant water detection methods primarily illustrate changes in plant water content by detecting variations in the apparent characteristics of plant moisture. During plant growth, there exists a water cycle system from soil to plant to atmosphere and back to soil. Detecting plant water content in water-saving irrigation systems can be achieved from any link in this system.

① Cell Sap Concentration and Water Content: There are mainly two methods for measuring plant cell concentration. The first is the comparative method, whose principle is to infer the cell's own concentration based on changes in cell morphology in sucrose solutions of different concentrations; the second method was proposed by Soviet scholar Lobov et al., whose principle involves comparing cell sap concentration with the percentage concentration of sucrose solution. Since sucrose solutions of different concentrations have different refractive indices, the extracted cell sap is placed in a refractometer to obtain the solution's refractive index, thereby determining the cell sap concentration.

② Stem Flow Measurement and Water Content: Current methods for measuring stem flow mainly include the following categories: heat pulse method, heat balance method, heat diffusion method, heat ratio method, and laser heat pulse method.

③ Leaf Water Potential: Leaf water potential reflects the energy level of water molecules in the cell sap of crop leaves. Methods for measuring leaf water potential domestically and internationally mainly include the following: small liquid flow method, pressure chamber method, and thermocouple psychrometer method.

④ Stem Diameter: Cell morphology changes under the influence of water content, and differences at the cellular level cause changes in stem thickness. This is the principle behind reflecting water content by detecting crop stem diameter.

⑤ Transpiration Rate: The magnitude of transpiration is the most direct indicator of plant water content. Various methods for measuring crop transpiration rate domestically and internationally include the following: steady-state porometer method, rapid weighing method, whole-tree container method, and isotope tracing method.

⑥ Canopy Temperature and Plant Water Content: Traditional thermometers are very inconvenient for large-scale measurements, and data collection and processing are difficult. With the development of infrared temperature measurement technology, plant water content detection using canopy temperature as a method began to develop. The commonly used method now is to represent crop water content using the difference between leaf canopy temperature (Ta) and ambient temperature (Tb).

⑦ Root Communication Substances: Under natural conditions, the organ that senses water stress in plants is the root, but the earliest response is the restriction of stomatal aperture and leaf growth. The information transmission from root to leaf must be achieved through specific media, which is abscisic acid. Therefore, plant water content can be reflected by detecting the abscisic acid content in plants.

⑧ Image Technology: Using image technology to measure plant water content is a method that has developed with the advancement of computer technology. The advantage of this method is that it allows for non-contact continuous measurement of crops, primarily obtaining crop water information through two approaches: the first is computer vision method, and the second is spectral method. The above methods are all based on detecting changes in a single trait within the plant for water content detection, each with its own advantages and disadvantages.