Method for producing a barrier layer in soil

The present invention relates to a method for producing a closing layer which improves the water and nutrient retention of soils, particularly of sandy soils, characterized in that a layer of clay mineral/polymer gel capable of binding and releasing water in a reversible manner is introduced into the soil, preferably 20-60 cm below the soil surface, in such a way that a clay mineral is reacted either before or after or during activation in the presence of water, with 0.5-30% by weight, calculated for the weight of the clay mineral, of one or more water-soluble polymer capable of reacting with the clay mineral, the water content of the resulting gel is adjusted either before or after or during the reaction to a value at which the resistance of medium of the gel is at least three times higher than that of a polymer-free suspension containing the same amount of the clay mineral, if a non-activated clay mineral has been applied as starting substance, the clay mineral is activated with an alkaline activating agent after reacting it with the polymer, and, if desired, further amounts of a water-soluble polymer, one or more water-insoluble swelling xerogel capable of at least 100% water uptake and forming swollen particles less than 1 mm in diameter and/or one or more chemical for agricultural use, preferably a plant nutrient, a fungicidal substance acting against soil-borne fungi and/or a plant growth increasing substance, is added to the gel either before or after or during the reaction with the polymer, and/or, if desired, the gel and the non-reacted polymer molecules are cross-linked with an aldehyde, and finally the thus-formed gel layer is covered with a soil layer.