A method is disclosed of in-situ retention and buffering of an amount of water in soil to support the growth of an agricultural crop. The method comprises the step of adding an effective amount of a hydrogel material as a water retention agent during planting of seed in the soil. The hydrogel material including an insoluble, cross-linked carboxymethyl cellulose. Once penetration of water into the soil is allowed after the planting of seed, a proportion of the water which penetrates the soil is absorbed by the hydrogel material and, over time, the absorbed water is released by diffusion into the soil to support the growth of the agricultural crop. Also disclosed is the hydrogel material which comprises said carboxymethyl cellulose which has been cross-linked with a cross-linking polymer from the group consisting of: an amine monomer； an amide monomer； and an amine-amide co-polymer.
