Superabsorbents and Semiarid Soil Properties Affecting Water Absorption.

Mixing cross-linked polyacrylamides with semiarid soils may increase water availability to crops. The effects of soils, sand, and superabsorbent properties on water absorption by four superabsorbent polymers (SAPs) were studied. The amount of water absorbed by the SAPs in tap water increased with increasing polymer cation exchange capacity. Less water was absorbed by SAPs mixed with soil or sand than by the control. In the sand and soil mixtures with a large-grain (3-4 mm) SAP, water absorption increased with time (up to 40-50 min) to a steady-state value in the range of 90 to 160 kg kg^-1 in the sand-SAP mixture and 33-55 kg kg^-1 in the soil-SAP mixture. Conversely, in the other three sod-SAP mixtures, water absorption reached a maximum value after 10 to 20 rain, followed by a decrease with time to values ranging between 20 and 60 kg kg^-1 At the initial stage of water absorption, confinement of the SAP grains by the soil particles was the dominant factor limiting water absorption by these SAPs; the confinement increased as soil texture became finer. The subsequent observed reduction was ascribed to the gradual replacement of Na or K cations that were adsorbed on the SAPs with Ca and Mg cations released from the soil. The results suggest that addition of a small amount of SAP to soils (5 g kg^-1 soil) is more effective at increasing water holding capacity in soils with low clay content than in soils with high clay content. [ABSTRACT FROM AUTHOR]