Water retention, hydraulic conductivity of hydrophilic polymers in sandy soil as affected by temperature and water quality

Hydrophilic polymers can swell by absorbing huge volumes of water or aqueous solutions. This property has led to many practical applications of these new materials, particularly in and regions for improving water retention in sandy soils and the water supply to plants grown on them. The effects of two hydrophilic polymers, carboxymethylcellulose (RF) and isopropyl acrylamide (BF) on the water holding capacity and saturated hydraulic conductivity (Ks) of a sandy soil at varying soil temperature and water quality were evaluated. The RF was less efficient in absorbing water than BF, but the efficiency of BF in retaining water was negatively affected by its thermo-sensitivity and the quality of water. The temperature dependence of the water absorption was not clear for the soils treated with RF, whereas, the efficiency of BF treatment in absorbing water decreased significantly (P < 0.05) with increasing soil temperature. The dependence of the Ks on soil temperature differed with the type of hydrophilic polymer used. The Ks of the control soil remained nearly constant as the soil temperature increased. The Ks of the BF treated soil increased significantly (P < 0.05) and linearly with increasing soil temperature, while that of soil treated with RF showed a quadratic response. The soil-absorbent mixtures exhibited different water retention characteristics under different soil temperature conditions. The increase in soil temperature did not affect the water retention characteristics curve of the control. The effect of soil temperature on the water potential curve of the soil treated with RF was not clear particularly when the temperature increased from 25 to 35 degrees C. The water potential curve for soil-BF mixtures showed that the water content value at field capacity shifted from 0.21 to 0.10 cm(3) cm(-3) for 0.1% and from 0.27 to 0.12 cm(3) cm(-3) for 0.2%, as the soil temperature increased from 15 to 35 degrees C. This implies that the soil-BF absorbent mixtures would release some moisture as the soil temperature would increase from 15 to 35 degrees C, and this water could be lost by percolation or taken up by plant. It was found that available water content increased up to four times with RF as compared to control soil whereas it increased up to five times with BF treatment. At high temperature, the difference was much reduced except for RF at 0.2%. This understanding of the characteristics of the absorbents and the interactions among absorbents, soil, and temperature would be of help in water management in sandy soil. (C) 2009 Elsevier B.V. All rights reserved.