Addition of hydrogels to soil for prolonging the survival of Pinus halepensis seedlings subjected to drought

The effect of an amendment of a sandy soil with superabsorbent hydrogels (S tockosorb K 400, a highly cross-linked polyacrylamide with about 40% of the amide group hydrolysed to carboxylic groups) on the survival of Pinus hale pensis seedlings during water stress was studied, with the following concen trations added to the soils: 0.04%, 0.08%, 0.12%, 0.20%, and 0.40%. The wat er retention of the soil increased exponentially with increasing additions of hydrogel to the soil. The highest concentration used changed the water r etention capacity and its change in water potential with regard to its wate r content from a typical sand to a loam or even silty clay. During desiccat ion under controlled conditions, the seedlings treated with 0.4% hydrogel s urvived twice as long in the soils amended with 0.4% hydrogel as in the con trol soils. During the drought, the seedlings exhibited a pronounced growth both of the shoot and the roots, which was about three-fold higher than th e one of the plants in the control soils. The data indicate that an amendme nt of soils with this type of hydrogels at 0.4% (w/w) will greatly enhance the drought tolerance of the seedlings growing on this substrate. A compari son between the reaction of the plants in the hydrogel amended soils and th e pF-curve measured with the plate test revealed that less water was actual ly available for the plants, as could be expected from the pF-curves. (C) 1 999 Elsevier Science B.V. All rights reserved.