Repeated water absorbency of super-absorbent polymers in agricultural field applications: a simulation study

Super-absorbent polymers (SAPs), a group of new water-saving materials and soil conditioners, have been widely adopted in agriculture, but little is known about their performances in repeated usage and other factors influencing SAPs' efficiency. Four types of commercial SAPs with organic macromolecules, labeled BF, JP, BJ, and WT, were taken with the aim of determining water-absorption capacity under different conditions, such as distilled water, tap water, soil extraction as the mixture of distilled water and soil, soil extraction as the mixture of tap water and soil, different temperatures, and varying soil drying degrees. After five absorption processes, the repeated water absorbencies in tap water, mixture of distilled water and soil, and mixture of tap water and soil were reduced by 73.4-99.3% relative to those in distilled water. Moreover, water quality had a greater effect on original water absorbency than soil extractions. Water absorbency increased with SAP's concentration, and such increases were reduced with repeated utilization. No significant differences in repeated water absorbency were found with varying temperatures (50, 25, and -4 degrees C). SAPs maintained excellent hydrophilic capacity for an extended period when the drying degrees of hydrogels were less than or equal to 80%. JP was initially considered to best sustain water absorption, followed by WT and BF. BJ showed the least absorption. The performances in repeated usage varied according to absorption stability, gel structure, application concentration of the SAPs, water quality, and soil moisture. Farmers can be recommended to use macromolecules JP and WT to improve crop production under altering dry-wet conditions.