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Currently, hydrogels are the most promising materials in polymer and materials science. Due to their soft and tissue-like properties and high water content, hydrogels have a wide range of applications, such as in tissue engineering and wound dressings. Agricultural hydrogels are characterized by excellent stability, high transparency, and low cost, and can be used as plant cultivation substrates.
As a hydrophilic substrate with high water content, agricultural hydrogels have unique quasi-solid properties that can directly provide water, air, and nutrients to plants. Moreover, this hydrogel is easy to produce and modify, affordable, thermally stable, and biodegradable. Therefore, it can be a good plant cultivation substrate. Additionally, hydrogels exhibit unparalleled advantages, especially when compared to traditional soil and soilless substrates.
Non-porous Substrates: Most agricultural hydrogels used as plant substrates are non-porous. The gelation of plant gum or agar during cooling forms gel blocks in containers such as petri dishes, fuchsia boxes, or test tubes. The medium is homogeneous with small visible pores, limited pore structure, low saturated hydraulic conductivity, and uniform distribution of nutrient ions.
Porous Substrates: Porous media can expand the root system's utilization of oxygen and water under heterogeneous conditions, stimulate plant physiological conditions, and promote plant growth. Therefore, this is a simple and effective way to overcome the limitations of non-porous gels. Various methods have been used to prepare porous cultivation substrates.
Agricultural hydrogels as cultivation substrates are mainly used in two major scenarios: Researching root structure and root-environment interactions, or improving soil quality by mixing with soil substrates. Hydrogels are commonly used as independent substrates for root structure and root environment studies, hence they need to have high transparency, strong mechanical properties, stability, controllability, and a porous structure. Hydrogels must have biocompatibility, degradability, and stimulus responsiveness to be used as soil conditioners.
Agricultural hydrogels are perfect candidates for soil amendments because of their numerous properties. The high water content and super adsorption capability of hydrogels help improve the water retention capacity of the soil. Unlike using hydrogels as a standalone substrate, research on soil amendments focuses more on the release mechanisms, as hydrogels are used to control or gradually release nutrients in the soil. Stimulus-responsive hydrogels, for example, contain units in their networks that react to stimuli.
Over the past few decades, agricultural hydrogels have been used as one of the most important tools in plant science research. They are used as plant growth substrates due to their outstanding benefits compared to soil and hydroponics. Currently, few plant cultivation substrates are functionalized, but with the development of hydrogel materials and construction methods, hydrogel-based plant cultivation substrates have the potential to be functionalized, providing more opportunities for plant science.
