Soil Treatment With Polymeric Hydrogen Siloxane

This invention relates to the use of a soil treatment composition by which it is possible to make the surface water-repellent and, hence, to obtain good water retention in the underlying layers.

The present invention addresses the problem of providing a composition which enables water retention to be improved, particularly under desert-like conditions. This objective is important because it is known that, under desert-like conditions, a certain proportion of the water is precipitated at the break of day and evaporates in the first few hours thereafter. The desired objective is to find a composition to enable this water to be retained in the soil. FR-PS 1 541 089 relates to a soil treatment process wherein an emulsion of asphalt and water applied in a quantity of up to 2 t/ha produces a retention of 30%. The disadvantage of this process is, on the one hand, the high application rate and, on the other hand, the inadequate retention.

The present invention relates to the use of a composition which, in a liquid carrier, contains a polymeric hydrogen siloxane (or (H) siloxane) corresponding to the following general formula ##STR2## in which

n is a number of from 1 to 70 and

R is an alkyl, hydroxyalkyl, aminoalkyl, haloalkyl or aryl radical.

In the present invention the liquid carrier is either water or an organic solvent. The hydrogen siloxane polymer is insoluble in water and forms an aqueous emulsion. The organic solvent is selected from the group consisting of alkanes, halogenated hydrocarbons, ketones and alkyl acetates, for example dichloromethane, methyl-ethyl ketones, ethyl, butyl or pentyl acetates, white spirit.

It is preferred to use water.

Two parameters have to be taken into account in evaluating the effect of the composition, namely water repellency and retention.

Water repellency is defined as the time taken by the water to pass through a soil which has been treated with one of the polymeric (H) siloxanes mentioned above. The time which the water takes to penetrate through the treated layer is a measure of water repellency and is normally between 5 and 30 minutes, which provides for a good accumulation of water.

Water retention is the percentage of water which remains beneath the layer of treated soil.

These two parameters are defined more closely hereinafter.

In the composition used, when the substituent R is an alkyl or a halo-alkyl, it may be a C.sub.1 -C.sub.18 and preferably C.sub.1 -C.sub.12 alkyl radical, more especially a methyl or fluoromethyl.

The number n is preferably from 5 to 45.

Thus, the present invention includes the use of a combination of a liquid carrier of water or dichloromethane and of polymeric (H) siloxane of the formula set forth above, wherein R is particularly a C.sub.1 -C.sub.18 alkyl or a haloalkyl, particularly methyl or fluoromethyl, and wherein "n" preferably is a number from 5 to 45.

The content of polymeric (H) siloxane in the soil layer is between 125 and 200 ppm (g/m.sup.3). The local surface treatment is preferably carried out with an (H) siloxane emulsion containing between 0.05 and 0.4% by weight of polymeric (H) siloxane. Aqueous solutions of polymeric (H) siloxanes are commercially available at the present time. They are applied in situ to the soil by conventional means of the type used for insecticides and fertilizers. The particular type of soil, above all sandy soils, is treated at 1-2 times per year. The mixture is distributed in such a way that a concentration of the polymeric (H) siloxane of from 10 to 40 kg/ha and preferably from 15 to 35 kg/ha is obtained on the soil, corresponding to 1-4 g/m.sup.2 and 1.5-3.5 g/m.sup.2, respectively.

10 Parts dry sand and 1 part (H) siloxane composition are mixed and the mixture is stirred for 4 hours at 50.degree. C. in a rotary evaporator. The siloxane-treated sand is uniformly applied in a layer thickness of 10 mm to a layer of dry untreated sand.

8-10 mm Water are then poured on and the time which this water takes to pass through the siloxane-treated sand is measured. Table I shows the results obtained with four different compositions.

The first three compositions show the greatest water-repellent activity. The most effective concentration for the first three products is 175 ppm which corresponds approximately to 2.6 g/m.sup.2.

The water penetrates through the thoroughly treated layer without wetting it and is taken up into the underlying untreated water-absorbing layer. The overlying layer acts as protection against daily evaporation and as transfer medium during the second phase of the daily cycle. Water retention is defined as the ratio between the water remaining and the water evaporated from the solid, water-saturated untreated phase.

It is determined by gravimetry and is expressed in %. ##EQU1## where

P.sub.o =loss, comparison value untreated

P.sub.t =loss from treated sand

If the treatment is ideal, the retention is 100%. If it is ineffective, the retention approaches zero. The following procedure is adopted:

A layer of dry untreated sand is used as the soil and a 10 mm thick layer of treated sand is applied thereto. The water required to saturate the sand (1 part water to 3 parts sand) is sprayed on the surface. The weight loss is determined in dependence upon the time after exposure to IR lamps which keep the surface temperature at 55.degree.-60.degree. C. To determine the retention value, it is essential to carry out the test under the same conditions with an untreated sample. Table II below shows the results obtained with the same products as in the water repellency test.

A retention above 50% is regarded as satisfactory. This level is achieved with the reacting polymethyl (H) siloxanes, i.e. the first three products in the Table.

150/200 ppm or g/m.sup.3 is regarded as an optimal application density.

The Example relates to the local (in situ) application by spraying of an emulsion of polymethyl (H) siloxane in various dilutions using a spray gun with a 1 mm diameter nozzle. 2.6 g/m.sup.2 Polymethyl (H) siloxane is applied to the surface in various dilutions. The test is carried out in accordance with the following scheme: dispersion of the emulsion of the agent (airgun, 1 bar), drying/reaction (1 day), surface application of water (1 g/cm.sup.2), gravimetric development as a function of time.

The measurements were conducted under normal temperature and pressure conditions at 60% relative air humidity.

The results are shown in Table III:

The concentration of the active agent in local application is an important factor and, in this Example, maximum retention is obtained with a concentration of 0.15% dry matter.

Examination of the results shows that, above 0.4%, the quantity of water is too small to allow adequate diffusion of the agent. Below 0.05% the quantity of water is too large, the diluted agent enters the lower layers where its concentration is too weak to have an adequate water-repellent effect.

Accordingly, the treatment according to the invention provides for the permanent presence of water in the soil, the quantity being sufficient for the development of a living culture under desert-like conditions.

It is sufficient to apply the polymeric (H) siloxane mentioned in the described manner one or two times a year because the polymer is slowly degraded under the effect of light.

The process according to the invention may also be combined with the process according to European patent 0 136 447. In this case, the composition according to the invention is mixed with an aqueous solution of a formaldehyde-based precondensate containing a condensation initiator. The second solution is applied to the soil in a quantity of 100 kg/ha to 500 kg/ha, based on dry matter. It is thus possible simultaneously to protect the soil against erosion and to obtain improved water retention.