Polyacrylamide/sodium alginate (PAAm/Na-alginate) crosslinked copolymers were prepared by using electron beam irradiation. The gel content and the swelling behavior of the obtained copolymers were investigated. The thermal and morphological properties of the prepared copolymers were studied using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The thermal stability of PAAm significantly changed when mixed with Na-alginate. The addition of PAAm/Na-alginate copolymer in small quantities to sandy soil increased its ability to retain water. The growth and other responses of the faba bean plant cultivated in a soil treated with PAAm and PAAm/Na-alginate copolymer were investigated. The growth of the bean plant cultivated in a soil containing PAAm/Na-alginate was better than that cultivated in soil treated with PAAm. The most significant difference between the PAAm and its alginate copolymer is that the latter partially undergoes radiolytic and enzymatic degradation to produce oligo-alginate, which acts as a plant growth promoter. The increase in faba bean plant performance by using PAAm/Na-alginate copolymer suggested its possible use in the agriculture field as a soil conditioner, providing the plant with water as well as oligo-alginate growth promoter. (c) 2006 Wiley Periodicals, Inc.