Method of stabilizing the soil and preventing erosion

The invention relates to a method of stabilizing the soil and preventing erosion. According to the invention such a method is characterized by treating the soil with a mixed product of a pre-gelatinized starch and 0.5-5% by weight, calculated on the dry starch, of a surfactant compound which contains an unbranched saturated alkyl group and is selected from the alkyl sulfates having 10-16 carbon atoms, the alkyl sulfonates having 10-16 carbon atoms and the fatty acid alcohols having 8-12 carbon atoms. The invention also relates to said mixed product.

The present invention relates to the stabilization of the soil by treating 
the surface of that soil with a mixture of a pre-gelatinized starch and 
certain surfactant compounds. 
Erosion of the soil is a major problem throughout the world. On account of 
its small particle size and its poor cohesion, finely-divided solid matter 
is sensitive to erosion. Such finely-divided matter is found in 
agricultural lands, dunes, at construction sites, in roads under 
construction, and in accumulations of sand, organic matter, inorganic 
matter, and waste matter. Erosion of the soil can occur under the 
influence of wind and rain. 
Erosion by wind causes the drifting of masses of dust. Erosion by wind 
causes the inconvenience of dust formation, the loss of valuable matter 
(humus, sowing seed, fertilizer, plantlets), and problems at building 
projects. Dust storms are a danger to traffic and a nuisance to persons 
staying at houses in the vicinity. Due to the drift of agricultural soil, 
sowing-seed, humus, and fertilizer can be blown away. In a later stage of 
plant growth, during dry periods, young plants are exposed as a result of 
erosion by wind, while the plantlets in locations out of the wind are 
covered by a layer of sand. Moreover, the plantlets are damaged by the 
abrasive action of the sand. In all of these cases the growth of young 
plants is seriously impeded or even made impossible. 
Erosion of the soil by rain can be caused by excessive rain, with the soil 
being washed away. In the process agricultural soil containing matter such 
as humus, sowing-seed, fertilizer or plantlets is washed away. Further, 
due to the influence of erosion by rain, the unprotected slopes of 
ditches, channels, dunes and roads may cave in. In numerous cases, 
therefore, it is extremely important to prevent or suppress erosion by 
wind and water. 
It has been proposed to prevent the shift, drift and washing away of soil 
by treating the surface layers of the soil with water-dispersible 
high-polymeric substances of a natural or synthetic nature. Examples in 
this connection are starch ethers, hydrolyzed polyacrylonitril, polyvinyl 
alcohol and carboxymethyl cellulose. U.S. Pat. No. 3,077,054 discloses the 
use of polyvinyl acetate, optionally in combination with starch ethers, as 
anti-erosion agents. U.S. Pat. No. 3,224,867 deals with the conditioning 
of the soil using mono starch phosphate. M. O. Weaver et al. 
(Starch/Staerke, 1984, pp. 56-60) describe the use of anionic starch 
derivatives for stabilizing the soil. The most important drawbacks of the 
polymers mentioned are their high price, their relatively poor biological 
degradability, their environment-foreign character and/or their 
potentially toxic properties. The starch ethers referred to moreover 
proved very sensitive to washing out by rain water. As a result, their 
action as an anti-erosion agent is often severely limited. 
Surprisingly, it has now been found that the soil can be stabilized against 
erosion by water and wind by treating that soil with a mixture of a 
pre-gelatinized starch and 0.5-5% by weight, calculated on the dry starch, 
of a surfactant compound containing an unbranched, saturated alkyl group, 
which compound is selected from the alkyl sulfates having 10-16 carbon 
atoms, the alkyl sulfonates having 10-16 carbon atoms and the fatty acid 
alcohols having 8-12 carbon atoms. 
For an important part, the stabilization of the soil is probably due to the 
fact that the surface layers of the soil are fixated to a certain extent. 
Here, the film-forming properties of the starch products to be used are of 
great importance. A treatment of the soil according to the method of the 
invention results in the formation of a poorly water-soluble, resilient 
crust at the surface of the mass treated, so that an excellent and 
relatively durable protection against wind and water erosion is obtained. 
In the method according to the invention the soil is treated with a mixture 
of pre-gelatinized starch and certain surfactant compounds. The 
pre-gelatinized starch can be prepared by roller-drying starch suspensions 
or starch solutions or by extruding granular starch. The pre-gelatinized 
starch obtained is swellable in cold water. The starch used may be derived 
from any suitable plant, and thus includes potato starch, tapioca starch, 
waxy maize starch, maize starch or wheat starch. These starches may be 
physically, enzymatically or chemically modified. Preferably, potato 
starch is used. 
The invention also relates to the mixed product to be used in the method, 
comprising pre-gelatinized starch and 0.5-5% by weight, calculated on the 
dry starch, of a surfactant compound which contains an unbranched 
saturated alkyl group and is selected from the alkyl sulfates having 10-16 
carbon atoms, the alkyl sulfonates having 10-16 carbon atoms and the fatty 
acid alcohols having 8-12 carbon atoms. 
The dispersibility and the film-forming characteristics of the 
pre-gelatinized starch can optionally be improved by adding, before 
roller-drying or extruding, alkaline substances, for example aqueous 
ammonia solutions, and/or boron compounds, for example borax to the 
starch. As a surfactant, preferably sodium lauryl sulfate is used. 
Optionally, yet other substances can be admixed with the pre-gelatinized 
starch, for instance water glass. Mixing the pre-gelatinized starch and 
the surfactant can be performed using any suitable mixing apparatus. 
Preferably, the surfactant is added to the pre-gelatinized starch in 
liquid condition, for example as an aqueous dispersion or as a molten 
product. The mixed product obtained is preferably in the form of an 
air-dry powder. A characteristic feature of the mixed product is that the 
product cannot be dissolved in water but yields an aqueous dispersion of 
swollen particles. These aqueous dispersions preferably have an alkaline 
pH, for example a pH between 9 and 11 in a dispersion of 5% by weight of 
mixed product in demineralized water. 
The mixed product to be used according to the invention can be applied to 
the soil to be treated as an air-dry powder or as an aqueous dispersion. 
When used for drift-sensitive, sand-containing grounds, the mixed product 
is preferably applied in the form of an aqueous dispersion with a 
dry-matter content of for instance 1-20%. The aqueous dispersion can be 
sprayed onto the soil to be treated via a spray boom or from a liquid 
manure spray comprising a pump and a splash plate. Broadcasting the mixed 
product in powder form is a possibility in some cases when sufficient dew 
formation enables the formation of a dense crust-like top layer. The 
amount of mixed product to be applied is strongly dependent on the nature 
of the soil to be treated and is preferably between 5 and 50 g of mixed 
product (dry matter) per square meter of soil. 
When the mixed products are being spread across the surface of the soil, 
the aqueous dispersion of the dry powder may contain various diluents or 
other additives. Examples in this connection are: sand, earth, clay, marl, 
chalk, bentonite, phosphates, mixed manure, agricultural chemicals, and 
trace elements. 
The mixed products used according to the invention form a protective crust 
together with the surface layer of the soil. It is true the adhesive 
starch particles swell up, but they do not lose their adhesive capacity. 
Reduced activity as a result of downward washing out due to rain will 
hardly occur, if at all. After drying the crust in the top layer recovers 
virtually completely. The granular components of the soil are bonded in 
such a way that the crust retains an open structure. Air- and 
water-permeability are sufficiently maintained. The sprouting of young 
plants is not impeded by the crust formed at the surface. 
A great advantage of the starch products to be used according to the 
invention is their biological degradability, which is only temporarily 
impeded by the surfactant component present. After about 4-6 weeks the 
mixed product appears to have lost its activity. Then begins the natural 
uptake of the starch into the soil environment under the influence of 
various micro-organisms. Although the treatment can be repeated then, the 
growth that has meanwhile developed will mostly provide for further 
resistance to erosion by water and wind. 
The invention will now be further explained in and by the following 
Examples.

EXAMPLE I 
140 l of an aqueous solution containing 25% by weight of ammonia and 100 kg 
borax.aq. were added to 9000 l aqueous potato starch suspension of 
22.degree. Be. The mass is gelatinized on heated rollers and dried. The 
roller-dried product is mixed with 227 kg sodium water glass solution of 
50.degree. Be and 337 kg of an aqueous solution containing 30% by weight 
of sodium lauryl sulfate. The product obtained is then ground. The mixed 
product thus obtained is used for the prevention of soil erosion. 
With moderate agitation 250 kg of the mixed product is added to 5000 l 
water in the storage tank of a spraying device. With intermittent 
agitation, after 30 min a ready-to-spray dispersion has formed of a 
viscosity suitable for further handling. Using a 2.times.9 m spray boom 
which is moved across a building site at a moderate speed, the suspension 
is distributed across the surface. The speed of the spraying device is 
adjusted so that about 2.5 kg of the mixed product is applied per are. 
After drying a tangible crust with an open structure is formed, 
effectively resisting drift up to wind velocities of 75 km/h. After 
several showers the protective effect is still well maintained. 
EXAMPLE II 
The mixed product according to Example I is mixed with an equal amount of 
mixed-manure matter. By means of a mechanical manure spreader the dry 
mixture is spread across the surface of the land in an amount of 500 
kg/hectare. Carrot seed is sown in rows in the field thus reared. The 
surface is then sprinkled with water by means of a sprinkler device. The 
sprinkling is repeated at intervals so as to maintain optimum growing 
conditions. The carrot seed sprouts and prospers. The dry top layer which 
is formed in the periods between the sprinkling phases proves to be 
drift-insensitive to winds of velocities up to ca. 75 km/h. 
EXAMPLE III 
The mixed product prepared according to Example I is spread across a 
drift-sensitive soil surface as a dry powder in an amount of 300 
kg/hectare. A mechanical manure spreader is used for this purpose. After 
just one morning of heavy dew sufficient bonding between the soil 
particles has taken place for a crust to begin to form which can 
effectively prevent erosion by wind. After a few periods of dew the 
formation of crust is yet further enhanced to a considerable extent. For 
an optimal effect through the method of dry application it is important 
that much attention be paid to a very homogeneous spread. 
EXAMPLE IV 
A clean vacuum manure tank is filled with 10,000 l water. At the same time, 
in the vacuum inlet system provided, 500 kg powdered mixed product from 
Example I is dispersed via an injection venturi. Agitation can be 
continued both mechanically and with injected air. The homogeneous 
dispersion is ready for use after 30 min. The spreading across the ground 
surface is carried out using the standard spray nozzle and splash plate. 
The spraying width is 12-18 m at 1.75 ato. In this manner the starch 
product is easily applied on a large scale with sufficiently homogeneous 
distribution. One tankful is sufficient for the treatment of a surface of 
2 hectares. Erosion by wind is thus strongly inhibited. 
EXAMPLE V 
100 g of the roller-dried product mixed with sodium water glass solution, 
is mixed with 2 g of a surfactant compound suitable according to the 
invention. The suitability of the obtained products as anti-erosion agents 
can be tested by means of standard tests. Their film-forming properties 
and the film-solubility (moisture-resistance) are particularly important 
here. To assay these properties first dispersions of 5% by weight of mixed 
product are prepared by agitating with tap water for 30 min. Film of a 
thickness of about 1.5 mm of these dispersions are smeared on a 
polyethylene foil-covered glass plate. Then these films are dried in the 
oven at 50.degree. C. 
Film formation: The film formation is sufficient when the swollen dispersed 
particles deliquesce during drying in such a way that a more or less 
closed film is formed. 
Film solubility: After the dried film is broken into particles smaller than 
2 mm, 0.50 of the product is weighed in a small glass beaker (50 ml, tall 
model). After the addition of 25 ml demineralized water, the dispersion is 
agitated at room temperature for 30 min using a magnet agitator (length 2 
cm). The dispersion obtained is transferred to a centrifugal tube and 
centrifuged at 300 rpm for 10 min. The supernatant is then decanted. The 
residual undissolved fraction is quantitatively transferred to a small 
weighed dish, followed by drying at 120.degree. C. in an oven until 
virtually all water has evaporated. Then it is determined by weighing how 
many grams of dry product the undissolved fraction contains (=y g). The 
film solubility (in %) is then defined as: 
##EQU1## 
Suitable mixed products possess a film solubility of less than 50% and 
preferably less than 25%. 
The results for a number of surfactants are shown in Table A. 
TABLE A 
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Film formation and film solubility of mixed products 
Surfactant substance 
Film formation 
Film solubility 
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Na-n-decyl sulfate 
reasonable 48% 
Na-dodecyl sulfate 
reasonable 16% 
Na-n-tridecyl sulfate 
reasonable 18% 
Na-n-tetradecyl sulfate 
moderate 14% 
Na-n-hexadecyl sulfate 
moderate 10% 
Na-1-dodecane sulfonate 
moderate 28% 
Octanol reasonable 44% 
1-Decanol reasonable 10% 
1-Dedecanol reasonable 18% 
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