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 (Stockosorb K 400, a highly cross-linked polyacrylamide with about 40% of the amide group hydrolysed to carboxylic groups) on the survival of Pinus halepensis seedlings during water stress was studied, with the following concentrations added to the soils: 0.04%, 0.08%, 0.12%, 0.20%, and 0.40%. The water retention of the soil increased exponentially with increasing additions of hydrogel to the soil. The highest concentration used changed the water retention capacity and its change in water potential with regard to its water content from a typical sand to a loam or even silty clay. During desiccation under controlled conditions, the seedlings treated with 0.4% hydrogel survived twice as long in the soils amended with 0.4% hydrogel as in the control soils. During the drought, the seedlings exhibited a pronounced growth both of the shoot and the roots, which was about three-fold higher than the one of the plants in the control soils. The data indicate that an amendment 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 comparison between the reaction of the plants in the hydrogel amended soils and the pF-curve measured with the plate test revealed that less water was actually available for the plants, as could be expected from the pF-curves.