Superabsorbent Polymer Properties and Concentration Effects on Water Retention under Drying Conditions

Core Ideas SAP amount for optimal water absorption is influenced by soil properties, SAP type and concentration. Soil–SAP mixtures had significantly greater water holding capacity compared with soil alone. Improvement in water holding capacity increased with an increase in SAP concentration. Improved retention is from reduced evaporation and from SAP absorption of water from soil during drying. Efficiency of SAP application depended on soil type, SAP type, SAP concentration, and their interactions. Superabsorbent polymer (SAP) efficiency in water absorption and release depends on soil properties and SAP type and concentration. Our objective was to examine the effects of soil texture, SAP concentration and properties on water absorption and release from soil–SAP mixtures during 10 h of drying. Four SAP types, five SAP concentrations, and five soils were used. Initial water quantity absorbed by SAPs (53–171 g g-1 of SAP) was more than two orders of magnitude greater than that absorbed by soils (0.35–0.53 g g-1 of soil). Water absorption by soil–SAP mixtures (i) significantly improved water holding capacity relative to the soil, and (ii) increased with an increase in SAP concentration and soil clay content. The ability of soil–SAP mixtures to retain water after 5 h of drying relative to the initial water content was greater than that of the soils alone, especially in coarse-textured soils. After 5 h of drying, the specific amount of water retained by a unit weight of SAP in the soil–SAP mixture was higher than that at 0 h. This observation suggests a continued absorption of water by SAPs from soils during the first 5 h of drying. The fraction of water loss from SAP with large-size beads (BJ-2101M) was smallest in all the mixtures among the four SAPs after 10 h drying. Our results showed that addition of SAPs to soils not only decreases water loss to evaporation from soils but also from the SAPs, especially for a SAP with large size beads.