Prodn. of sub-surface moisture barrier gel layer in soil

Prodn. of a barrier layer which improves the water and nutrient retention of soils, partic. sandy soils, is characterised in that: a layer of clay mineral/polymer gel capable of reversibly binding and releasing water is introduced into the soil, pref. 20-60cm below the surface, in such a way that the clay is reacted before or after or during activation in presence of water, with 0.5-30 wt. % (on wt. of clay) of water-soluble polymer(s) capable of reacting with the clay; the water content of the resulting gel is adjusted before or after or during reaction to a value at which the resistance of medium of the gel is at least 3 times higher than that of a polymer-free suspension contg. the same amt. of clay, if non-activated clay was used; the clay mineral is activated with an alkaline activating agent after reacting with the polymer; if desired, further amts. of water-soluble polymer, water-insoluble swelling xerogel(s) capable of at least 100% water uptake and forming swollen particles less than 1mm in dia., and/or agricultural chemical(s), pref. plant nutrient, soil fungicide and/or plant growth promotant, is added to the gel before or after or during reaction with the polymer; and/or, if desired, the gel and the non-reacted polymer molecules are crosslinked with an aldehyde; and, finally, the obtd. gel layer is covered with a soil layer.