Synthesis of Nanocomposite Hydrogels for Improved Water Retention in Horticultural Soil

Global desertification and shortage of agricultural water are occurring because of climate change such as prolonged drought and erratic rainfall. Accordingly, a means by which moisture can be retained in soil to sustain plants' growth in such harsh environmental conditions using polymer hydrogels (PHGs) has been developed. For PHGs for soil moisturization, the chains within the polymer are hydrophilic, and the polymer chains can contain water. PHGs have been used extensively to improve the water availability of plants by increasing the water retention of soils and substrates, and the application of hydrogel polymers may be an appropriate technique to improve the efficiency of water and fertilizer use. In this study, a nanocomposite (NC) hydrogel with a uniform cross-linked structure was successfully prepared using laponite, an inorganic nano-sheet, as PHGs for soil moisture retention. The prepared NC hydrogel was characterized through transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) and showed complete exfoliation of inorganic nano-sheets. The synthesized NC hydrogel is derived from potassium acrylate (KA)-containing potassium, which is an effective ion for plant growth and achieves complete swelling in about 20 min. In addition, it is possible to adjust the swelling characteristics by adjusting the ratio of KA and has a swelling characteristic of 100-300 g/g (vol of water per dry hydrogel wt) suitable for horticulture. The synthesized NC hydrogel was not affected by pH and the presence of inorganic salts and could swell up to 100 g/g in saline water. These properties mean that the NC hydrogel can be used as a superabsorbent polymer (SAP) in soil. The growth of cucumbers and tomatoes in NC hydrogel-amended soil did not negatively impact the physiological characteristics and shoot and root development.