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Influence of Hydrogel Type and Concentration, and Water Application Rate on some Hydraulic Properties of a Sandy Soil

Ahmed M. Abdallah

Water percolation and storage in a model sandy soil amended with four superabsorbent polymers (SAPs) was investigated using drip irrigation with two discharge rates. Superabsorbent polymers (Watersorb, Ag-SAP, Tera-Gel and Water-crystals) were mixed with the soil at three concentrations [0.2% or 0.4% (W/W) and control (0.0%)]. All soil columns received a fixed amount of water at two discharges i.e., 2.0 or 4.0 L h-1. The percentages of percolated and retained water (relative to total water applied), gravimetric soil water content (G-wc) and bulk density (BD) were determined. All SAPs, at any concentration and water application rate, reduced the percentage of percolated water (PPW) and BD and increased the total soil porosity (TP). The reduction of PPW resulted in increases in soil water storage that were proptional to SAPs concentration. Under low water application rate, SAPs were more efficient as compared with high water application rate, because SAPs had enough time to reach their maximum water absorption capacity (WAC). At a SAPs concentration of 0.4% and low water application rate, Watersorb, Tera-gel and Ag-sap were acting equally and were best performing, as the G-wc increased by 2.6 folds compared to control. However, at the high water application rate, SAPs with higher water absorption rate “WAR” (Watersorb) worked best, as its particles swell faster. It can be concluded that, WAC of SAPs is important when irrigation water application rate is low and at high water application rate, WAR would be the most important property allowing SAPs to reach complete water absorption during short irrigation duration.

Key words: water application rate, percolation, water absorption capacity, soil water storage, superabsorbent polymers (SAPs)