WO2019030183A1

WO2019030183A1 - Method for improving the water retention of soils

Info

Publication number: WO2019030183A1
Application number: PCT/EP2018/071302
Authority: WO
Inventors: Mauro Riccaboni; Serena GAZZO; Rocco Di Modugno; Giovanni Floridi; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2017-08-08
Filing date: 2018-08-06
Publication date: 2019-02-14
Also published as: IT201700091543A1

Abstract

The present invention relates to a method for improving the water retention of a soil comprising the application of a derivatized tamarind gum.

Description

METHOD FOR IMPROVI NG THE WATER RETENTION OF SOI LS

TECHNICAL FIELD

This invention also pertains to compositions comprising said derivatized tamarind gums.

PRIOR ART

Plants require specific amounts of moisture to germinate, to grow and to remain viable. In conditions of water scarcity and/or high evaporation/ transpiration, soil loses water rapidly due to high temperatures, low humidity, high winds and plant transpiration. Moisture in the soil is drawn to exposed soil surfaces by capillary action and lost by evaporation into the air. At the same time, moisture drawn from the soil into plant root fibers by osmosis is transpired through the plant stems and leaf systems, and that fraction not converted by photosynthesis is then lost by evaporation from pores of leaf surfaces. Under such conditions, the volumetric water content of the soil can decrease significantly.

Moreover, rainy or irrigation water distributed onto coarse, sandy soils, can move past the plant root zone due to channeling, defined as the rapid movement of water downward through large pore spaces, and lack of retention, caused by lack of organic matter available to absorb water. Also water repellent soils present significant hydrologic and agronomic challenges. Since they are characterized a particular surface chemistry that impedes or completely inhibits hydration, they show reduced water infiltration into the soil (leading to runoff and heavy erosion) and strong effects on the regular growth and maintenance of turf grass and a variety of agricultural crops.

Furthermore, where there is a marked change in ground temperatures between day and night, there is a significant air inhalation into porous soils during the night-time cooling (contraction) cycle and exhalation of air and moisture in the heat of the day. This further aggravates the overall evaporative moisture loss.

Moisture is typically added to the soil by watering using manual or automatic means, such as sprinkler and drip irrigation systems. Such systems must nevertheless be connected to expensive and elaborate irrigation conduits and controls, which severely limit usage and have high energy consumption.

A further method for maintaining the ground moisture, utilizes the sponge like materials which are previously mixed with the soil surrounding the plant roots and then imbued with water during the sprinkling watering either natural or artificial. These materials usually are not biodegradable and contaminate the soils in which are inserted.

Many methods use water retention agents as soil conditioner to increase volumetric water content. The water retention agents are usually (co)polymers of natural, semi-synthetic or synthetic origin.

These (co)polymer can be directly applied to or mixed with the soil or can be used to prepare moisturizing agent, usually aqueous solution or suspension, which is applied to the soil surface. The application can be accomplished in variety of ways, including but not limited to, spraying, casting, mulching, plowing or otherwise incorporating into the top layers of soils.

Several patents, as described below, disclose a variety of polysaccharides and polysaccharide derivatives suitable as water retention agents for improving water management.

US 2011/003936 relates to methods and compositions relating to soil additives that hydrophilize soil particles and/or increase available water capacity in soil . The soil additive can be a polymer comprising a polysaccharide of plant origin or an anionic, neutral or cationic derivative thereof, including galactomannans, such as guar gum and cassia gum, and their derivatives; starch and starch derivatives; cellulose and cellulose derivatives; xylan, arabinoxylan, glucans, xyloglucans, and other plant cell wall hemicelluloses; and the like. Among the xyloglucans, unmodified tamarind gum is mentioned .

US 2013/036668 describes a peat moss composition having improved water holding capacity, hydrophiiicity, and/or anti-leaching properties comprising one or more polysaccharides. Suitable polysaccharides include guar and various guar derivatives, cellulose and cellulose derivatives, starch, chitosan, alginate, xanthan gum, tamarind gum, etc.

US 2004/068073 discloses method of producing and using a starch graft copolymer. These copolymers, applied on field crops, provide excellent anti-crusting properties, increased seed germination and stand, increased crop growth, increased crop yields and reduced water requirements.

WO 2007/146055 describes a substrate, which releases impregnated water, gas and nutrients when interacting with biological organisms, comprising a mixture of a salt of carboxymethyl cellulose compound, having an average molecular weight ranging between 90,000 and 700,000, a hydrated metallic salt, water, a micro-nutrient selected from the group consisting of zinc and zinc salts, at least one plant growth additive selected from the group consisting of plant growth hormones and plant growth regulators, at least one preservative, a surfactant, and an acetic acid component selected from the group consisting of acetic acid or acetic acid salts.

JP 2000/166380 describes a gel composition for slowly dispensing water to growing plants comprising an anionic water-soluble polymer crosslinked with a metal ion selected from the group consisting of aluminum, magnesium and calcium. The anionic polymer can be chosen among alginate, carboxymethyl starch and carboxymethyl tamarind .

Sometimes, when the watering process is supposed to be optimized for the growing conditions, localized dry spots ("LDS") may take place also in the presence of a water retention agent. It can be caused by excessive thatch, compacted soil, poor irrigation coverage, steep sloping grade (water runoff), high soil salinity, improper chemical usage, insects, diseases and water-repellent soil . LDS is characterized by irregular, isolated, hydrophobic areas problematic in the crop or turf stand.

The number of localized dry spots can be minimized by using surfactants in combination with the water retention agents. In fact the surfactants acting as wetting agent allow water to spread horizontally and to penetrate to a useful depth through the small channels and capillaries of the soil without being repelled or retained mainly on the surface or in defined area.

This solution is described in WO 02/15687, which relates to soil treatment compositions comprising : an active ingredient selected from the group consisting of water soluble or dispersible polymers and a surfactants, or a combination of these two ingredients; and the balance carriers and other adjunct ingredients. The water soluble or dispersible polymer can be a polysaccharide such as a cellulosic polymer, for example carboxymethyl cellulose or hydroxyalkyl cellulose, xanthan, pectin, gum arabic, guar gum, carageenan, etc.

Usually, the water retention agents are applied on soil as moisturizing agents, typically as aqueous solutions which are prepared at the application site. It is important that all the components of the moisturizing agents are correctly dosed and well dissolved to ensure that no under dosing or overdosing on the soil is obtained .

However, the polysaccharides and derivatives thereof can be difficult to be used in field situations and in solid form they take a long time to dissolve, also under high shear stirring.

A good solution to this problem is to prepare a concentrated aqueous composition of a polysaccharide or a derivative thereof and surfactants which can be easily dosed and homogenized .

Unfortunately, it is difficult to combine adequate quantities of a polysaccharide or a derivative thereof and surfactants in concentrates and/or to obtain stable compositions in all cases. Furthermore, the type of surfactant will be limited to those compatible with the specific polysaccharide or derivative thereof.

Accordingly, there is still a need for a water retention agent based on a polysaccharide, which can be easily dissolved and applied, which possibly does not require the addition of a surfactant, has increased efficacy on any kind of soil and can improve the water usage efficiency of plants and grasses.

We have now discovered that derivatized tamarind gums possess all the required characteristics and can be advantageously used as an efficient water retention agent even without the addition of a surfactant. The derivatized tamarind gums of the invention show higher water retention performances compared with underivatized tamarind gum or other derivatized polysaccharides/gums and can be directly applied to the soil or can be easily dissolved in water at the application or mixing site to prepare ready-to-use liquid moisturizing agents.

The derivatized tamarind gums of the invention reduce the losses of moisture from direct evaporation or from channelling, improves the proportion of soil moisture accessible to plants, and in certain conditions prevents or even reverses the evaporative loss from day/night movement in and out of porous soils.

Moreover, they can also be provided as concentrated compositions containing, besides the derivatized tamarind gums, high amount of other additives commonly used in the field . These concentrates are stable, pourable and can be easily dissolved/diluted at the application or mixing site to prepare ready-to-use moisturizing agents.

As far as the Applicant knows, no one has disclosed the use of the non-crosslinked derivatized tamarind of the invention as water retention agent.

US 2011/003936 and US 2013/036668 describe the use of various polysaccharides of different nature as water retention agents. Tamarind gum is mentioned among these polysaccharides, but no further descriptions nor examples with performances data are given. The use of derivatized tamarind gum is not mentioned or even suggested.

JP 2000/166380 discloses carboxymethyl tamarind for water retention which is heavily crosslinked with polyvalent metals to form structured gels retaining large amount of water and having excellent shape retention. When dried, these gels may be reconstituted by simple hydration. The gels are used for guaranteeing the supply of water for long periods.

JP 2000/166380 is silent about the water retaining capability of non-crosslinked derivatized tamarind, that as such do not form steady gels and therefore cannot stably bond large amounts of water.

In the present invention, the derivatized tamarind are used in non-crosslinked form, preferably as water soluble powders or in the form of aqueous solutions, for irrigation on-field and for similar applications.

With the expression "derivatized tamarind gum", we mean that the tamarind gum is modified by reacting its hydroxyl groups with one or more derivatizing agents under appropriate reaction conditions to produce a polysaccharide chain having covalently linked the desired substituent groups, such as a cationic, non-ionic, anionic and/or hydrophobic substituent groups, or a precursor of such a substituent groups. Suitable derivatizing reagents are commercially available and typically contain a reactive functional group, such as an epoxy group, a chlorohydrin group, or an ethylenically unsaturated group, which react with the hydroxyl group, and at least another substituent group, i.e. those mentioned above, per molecule. Typical examples of these derivatized tamarind gums are: hydroxyalkyl tamarind, carboxyalkyl tamarind, cationic tamarind and hydrophobically modified tamarind.

DESCRIPTION OF THE INVENTION

It is, therefore, an object of the present invention a method, for improving the water retention of soil, comprising the application on the soil of from 0.05 to 5.0 kg/ha, preferably from 0.1 to 3.5 kg/ha, more preferably from 0.5 to 2 kg/ha, of a derivatized tamarind gum, by which the water retention of the soil is improved.

DETAILED DESCRIPTION OF THE INVENTION

Tamarind (Tamarindus Indica) is a leguminous evergreen tall tree which grows in the tropics. Tamarind gum (tamarind powder or tamarind kernel powder) is obtained by extracting and purifying the powder obtained by grinding the seeds of tamarind.

Tamarind gum is a complex mixture containing a xyloglucan polysaccharide (55-75 % wt), proteins (16-22 %wt ), lipids (6-10 % wt) and certain minor constituents such as fibres and sugar.

The polysaccharide backbone consists of D-glucose units joined with (l-4)-p-linkages similar to that of cellulose, with a side chain of single xylose unit attached to every second, third and fourth of D-glucose unit through a-D-(l-6) linkage. One galactose unit is attached to one of the xylose units through p-D-(l-2) linkage.

There are basically two different grades of tamarind gum which are used in specific industrial applications like textile and pharmaceutical industries: oiled tamarind kernel powder and the de-oiled tamarind kernel powder. Both are useful for preparing the derivatized tamarind gum of the present invention.

Other tamarind gums which have been subjected to some treatment before the derivatization, such as enzymatic treatments or physico-chemical treatments, are also useful for the realization of the present invention. The tamarind gum suitable for being derivatized has preferably a Brookfield® RV viscosity, measured at 25 °C and 20 rpm on a 5.0 % wt water solution, comprised between 100 and 30,000 mPa*s.

As described above, the derivatized tamarind gum of the method of the invention can be obtained by reaction of a tamarind gum with a derivatizing agent, which binds non-ionic, anionic, cationic or hydrophobic substituent groups on the polysaccharide chain, or with combinations of said derivatizing agents.

According to the invention, the derivatized tamarind gum therefore can contain non-ionic substituent groups, such as hydroxyalkyl groups (hydroxyalkyl tamarind). In a preferred embodiment of the invention, the derivatized tamarind gum is a hydroxyalkyl tamarind having a hydroxyalkyl molar substitution (MS) comprised between 0.1 and 3.0, preferably between 0.1 and 1.5, more preferably between 0.1 and 1.0.

With the expression "hydroxyalkyl molar substitution", we mean the average number of hydroxyalkyl substituents on each anhydrogiycosidic unit of the polysaccharide measured by means of ^-NMR.

The process for introducing a hydroxyalkyl group on a polysaccharide, wherein the alkyl represents a straight or branched hydrocarbon moiety having from 1 to 5 carbon atoms (e.g., hydroxyethyl, or hydroxypropyl, hydroxybutyl), is well known in the art.

Typically, the hydroxyalkylation of a polysaccharide is obtained by the reaction with reagents such as alkylene oxides, e.g . ethylene oxide, propylene oxide, butylene oxide and the like, to obtain hydroxyethyl groups, hydroxypropyl groups, or hydroxybutyl groups, etc.

The derivatized tamarind gum of the invention can also contain anionic substituent groups, such as carboxyalkyl (carboxyalkyl tamarind) or sulfoalkyl groups.

Thus, in another embodiment, the derivatized tamarind gum is a carboxyalkyl tamarind, with a degree of carboxyalkyl substitution (DS_an) comprised between 0.01 and 1.2, preferably between 0.05 and 0.8.

With the expression "degree of carboxyalkyl substitution", we mean the average number of hydroxyl groups substituted with a carboxyalkyl group on each anhydrogiycosidic unit of the polysaccharide measured by means of ^!H-NMR. Halo-carboxylic acids or their salts can be used for the preparation of carboxyalkyl tamarind . The preferred halo-carboxylic acid is monochloro-acetic acid .

The carboxyalkyl tamarind of the invention is obtained in the form of a salt of alkali metal ions, such as sodium or potassium. Preferably, the carboxyalkyl tamarind of the invention is a potassium or sodium salt, more preferably a potassium salt.

In a further preferred embodiment, the derivatized tamarind gum of the invention is a cationic tamarind and has a degree of cationic substitution (DScat) comprised between 0.01 and 1.0, preferably between 0.05 and 0.6. In the present text, with the expression "degree of cationic substitution", we mean the average number of hydroxyl groups substituted with a cationic group on each anhydroglycosidic unit of the polysaccharide determined by means of ^-NMR.

Cationic groups can be introduced on the tamarind gum by reaction of part of the hydroxyl groups of the xyloglucan gum with cationization agents, such as tertiary amino or quaternary ammonium alkylating agents. Examples of quaternary ammonium compounds include, but are not limited to, glycidyltrialkyl ammonium salts, 3-halo-2-hydroxypropyl trialkyl ammonium salts and halo-alkyltrialkyl ammonium salts, wherein each alkyl can have, independently one of the other, from 1 to 18 carbon atoms. Examples of such ammonium salts are glycidyltrimethyl ammonium chloride, glycidyltriethyl ammonium chloride, gylcidyltripropyl ammonium chloride, glycidylethyldimethyl ammonium chloride, glycidyldiethylmethyl ammonium chloride, and their corresponding bromides and iodides; 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, 3-chloro-2- hydroxypropyltriethyl ammonium chloride, 3-chloro-2-hydroxypropyl tripropyl ammonium chloride, 3-chloro-2-hydroxypropylethyldimethyl ammonium chloride, 3-chloro-2-hydroxypropylcocoalkyldimethyl ammonium chloride, 3-chloro- 2-hydroxypropylstearyldimethyl ammonium chloride and their corresponding bromides and iodides.

Examples of halo-alkyltrialkyl ammonium salts are 2-bromoethyl trimethyl ammonium bromide, 3-bromopropyltrimethyl ammonium bromide, 4-bromobutyltrimethyl ammonium bromide and their corresponding chlorides and iodides.

Quaternary ammonium compounds such as halides of imidazoline ring containing compounds may also be used .

Typically, the cationizing agent is a quaternary ammonium compound and more preferably is 3-chloro-2-hydroxy propyltrimethyl ammonium chloride. The cationic substituent is in this case a chloride of a 2-hydroxy-3-trimethyl ammonium propyl ether group.

In another preferred embodiment, the derivatized tamarind gum of the invention contains hydrophobic substituent groups and is a hydrophobically modified tamarind having a degree of hydrophobic substitution (DSH) of from 1*10^"5 to 5*10^_1, preferably from 1*10^"4 to 1*10^_1.

With the expression "degree of hydrophobic substitution", we mean the average number of hydrophobic substituents on each anhydroglycosidic unit of the polysaccharide measured by means of gas-chromatography or ^!H-NMR.

The hydrophobization of the tamarind gum of the invention is achieved by the introduction of hydrophobic group. Examples of the introduction of hydrophobic groups on polysaccharides are reported in EP 323 627 and EP 1 786 840.

Typical derivatizing agents bringing a hydrophobic group include linear or branched C2-C24 alkyl and alkenyl halides, linear or branched alkyl and alkenyl epoxides containing a Ce-C₂₄ hydrocarbon chain and alkyl and alkenyl glycidyl ethers containing a C₄-C₂4 linear or branched hydrocarbon chain. A suitable glycidyl ether hydrophobizing agent can be, for example, butyl glycidyl ether, t-butyl glycidyl ether, 2-ethylhexyl glycidyl ether, dodecyl glycidyl ether, hexadecyl glycidyl ether, behenyl glycidyl ether and nonylphenyl glycidyl ether.

Representative alkyl epoxides include but are not limited to 1,2-epoxy hexane, 1,2-epoxy octane, 1,2-epoxy decane, 1,2-epoxy dodecane, 1,2-epoxy tetradecane, 1,2-epoxy hexadecane, 1,2-epoxy octadecane and 1,2-epoxy eicosane.

Exemplary halide hydrophobizing agents include but are not limited to ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyl, neopentyl, hexyl, octyl, decyl, dodecyl, myristyl, hexadecyl, stearyl and behenyl bromides, chlorides, and iodides.

Other derivatizing agents suitable for the hydrophobic modification include alkyl- and alkenyl^-hydroxy-y-chloropropyl ethers and epoxy derivatives of triglycerides.

In an embodiment of the invention, the hydrophobic substituent contains a linear alkyl or alkenyl chain containing between 6 and 24 carbon atoms or a mixture of such alkyls or alkenyls.

In the method of the invention the hydroxyalkyi tamarind, alkali metal salts of carboxyalkyl tamarind, cationic tamarind and hydrophobically modified tamarind are used in non-crosslinked form.

When the derivatized tamarind gum contains a combination of substituent groups, for example non-ionic and anionic or cationic and hydrophobic, the degrees of substitution (DSAN, DS_cat and DS_H) and the molar substitution (MS) are comprised within the ranges described above.

The derivatized tamarind gum of the present invention can be prepared by known processes. For example, the non-ionic, anionic cationic and hydrophobic groups can be introduced by reaction of the tamarind gum with the derivatizing agent, in the presence of a base, such as sodium hydroxide. The introduction of more substituent groups on the tamarind gum backbone, e.g cationic and hydrophobic groups, can follow any order. When the derivatized tamarind gum of the invention also contains hydroxyalkyl substituents, they may also be introduced in the last step, after carboxymethylation, cationization and hydrophobization have occurred .

In an exemplary production process, the derivatized tamarind gum is obtained operating as follows: tamarind gum, possibly dispersed in water or an inert diluent which can be chosen among lower aliphatic alcohols, ketones, or liquid hydrocarbons, or mixtures of the above, is treated at ambient temperature with an alkali-hydroxide in aqueous solution and then heated to 50-90 °C. The reaction mass system is then set to about 50 °C and the derivatizing agent, such as ethylene oxide and/or propylene oxide and/or monochloroacetic acid, are introduced into the reactor, possibly dispersed in inert organic diluents. The reaction is completed by setting the temperature at 40-80 °C for 1-6 hours.

At the end of this preparation, the derivatized tamarind gum consists of modified polysaccharide, by-products formed during the reaction and salts deriving from neutralization of the residual alkali hydroxide. The carboxyalkyl tamarind is directly obtained in the form of alkali metal salt and it is not subjected to any further reaction step.

After the preparation, the derivatized tamarind gum can be modified by treatment with reagents, such as caustic and acids; or it can be oxidated with biochemical oxidants, such as galactose oxidase; or it can be depolymerized with chemicals, such as hydrogen peroxide or strong acids, or with enzymatic reagents. Reagents such as sodium metabisulfite or inorganic salts of bisulfite may also be optionally utilized.

In another embodiment, the derivatized tamarind gum is further modified by physical methods using high speed agitation machines or thermal methods. Combinations of these reagents and methods can also be used. These modifications can be also performed on the tamarind gum before the derivatization process.

In a preferred embodiment, the derivatized tamarind gum is a depolymerized derivatized tamarind gum, which has been depolymerized by using suitable chemicals, such as mineral acids or hydrogen peroxide, or cellulase enzymes.

In a further embodiment, a purification of the derivatized tamarind gum can be performed after the derivatization to obtain a particularly pure suitable product.

The purification step may take place by extraction of the impurities with water or aqueous-organic solvent before a final drying step so as to remove the salts and by-products formed during the reaction.

In a further preferred embodiment, the tamarind gum derivative of the present invention is left unpurified (usually called "crude" or technical grade) and still contains by-products generated during its chemical preparation (that is during the derivatization).

This unpurified derivatized tamarind gum can contain from 4 to 65 % by dry weight of by-products, such as inorganic salts deriving from the neutralization of the bases used for the reaction, glycols and polyglycols deriving from the alkylene oxides, cationizing agents and their degradation products, etc.

The weight average molecular weight (M_w) of the derivatized tamarind gum useful for the invention typically ranges between 10,000 and 4,000,000 dalton.

The weight average molecular weight of the derivatized tamarind gum can be determined by gel permeation chromatography using a set of pullulan standards for the system calibration. In a preferred embodiment the weight average molecular weight of the derivatized tamarind gum is comprised between 100,000 and 1,000,000 dalton and more preferably between 250,000 and 800,000 dalton.

In another preferred embodiment the weight average molecular weight of the derivatized tamarind gum is comprised between 10,000 and 100,000 dalton and more preferably between 15,000 and 80,000 dalton.

In a specific preferred embodiment of the invention, the derivatized tamarind gum contains only hydroxyalkyl, in particular hydroxypropyl, groups and has a MS comprised between 0.1 and 1.0.

In another preferred embodiment of the invention, the derivatized tamarind gum contains only carboxyalkyl, in particular carboxymethyl, groups and has a DSan ranging from 0.05 to 0.5.

In a further preferred embodiment of the invention, the derivatized tamarind gum contains only cationic groups and has a DS_cat comprised between 0.05 and 0.45.

In a even further preferred embodiment, the derivatized tamarind gum of the invention contains hydroxyalkyl groups and at least another substituent group chosen among anionic, cationic and hydrophobic groups. In this case, the MS is comprised between 0.1 and 3.0, the DS_an is between 0.01 and 1.2, the DScat is between 0.01 and 1.0 and the DS_H is between 1*10^~5 and 5*10^_1. In a more preferred embodiment, the derivatized tamarind gum of the invention is a hydroxypropyl tamarind and has a MS comprised between 0.1 and 0.8 and a weight average molecular weight comprised between 100,000 and 1,000,000 dalton.

In another more preferred embodiment, the derivatized tamarind gum of the invention is a carboxymethyl tamarind, has a DS_an ranging from 0.05 to 0.5 and a weight average molecular weight comprised between 10,000 and 100,000.

The derivatized tamarind gum of the invention is a powder, which can be used as such or dissolved/dispersed in water just before use. In another aspect of the invention, the derivatized tamarind gum is provided as an aqueous solution or dispersion comprising from 10 to 50 wt%, as dry matter of derivatized gum, preferably having a Brookfield® viscosity comprised between 10 and 5000 mPa*s, preferably between 100 and 2500 mPa*s.

According to a further embodiment of the invention, the derivatized tamarind gum is provided in a composition comprising :

a) from 10 to 50 wt%, preferably from 10 to 40 wt%, more preferably from 12 to 30 wt%, of said derivatized tamarind gum;

b) from 0.2 to 30 wt%, preferably from 0.2 to 20 wt%, more preferably from 0.5 to 10 wt%, of at least a surfactant,

that is applied onto the soil after dilution.

Anionic, cationic, non-ionic and ampholytic surfactants and mixtures thereof can be used as the surfactant b).

Suitable non-ionic surfactants are, for example:

• polyalkoxylated, preferably polyethoxylated, saturated and unsaturated aliphatic alcohols, having 8 to 24 carbon atoms in the alkyl radical, which can be derived from the corresponding fatty acids or from petrochemical products, and having 1 to 100, preferably 4 to 40, ethylene oxide units (EO);

• polyalkoxylated, preferably polyethoxylated, arylalkylphenols, such as, for example, tristyrylphenol having an average degree of ethoxylation of between 8 and 80, preferably from 16 to 40;

• polyalkoxylated, preferably polyethoxylated, alkylphenols having one or more alkyl radicals, such as, for example, nonylphenol or tri-sec-butylphenol, and a degree of ethoxylation of between 2 and 40, preferably from 4 to 20;

• polyalkoxylated, preferably polyethoxylated, hydroxy-fatty acids or glycerides of hydroxy-fatty acids, such as, for example, castor oil, having a degree of ethoxylation of between 10 and 80; • sorbitan or sorbitol esters with fatty acids or polyalkoxylated, preferably polyethoxylated, sorbitan or sorbitol esters;

• polyalkoxylated, preferably polyethoxylated, amines;

• di- and tri-block copolymers, for example from alkylene oxides, for example from ethylene oxide and propylene oxide, having average molar masses between 200 and 8000 g/mol, preferably from 1000 to 4000 g/mol;

• alkylpolyglycosides or polyalkoxylated, preferably polyethoxylated, alkylpolyglycosides.

Preferred non-ionic surfactants are polyethoxylated aliphatic alcohols, preferably from renewable resources, such as ethoxylated (4-8 EO) C12-C14 natural alcohol; polyethoxylated triglycerides of hydroxy-fatty acids and polyethylene oxide/polypropylene oxide block copolymers.

Also suitable are anionic surfactants, for example :

· polyalkoxylated, preferably polyethoxylated, surfactants which are ionically modified, for example by conversion of the terminal free hydroxyl function of the alkylene oxide block into a sulfate or phosphate ester;

• alkali metal and alkaline earth metal salts of alkylarylsulfonic acids having a straight-chain or branched alkyl chain;

• alkali metal and alkaline earth metal salts of paraffin-sulfonic acids and chlorinated paraffin-sulfonic acids;

• alkali metal and alkaline earth metal salts of sulfate or phosphate ester of C8-C24 saturated and unsaturated aliphatic alcohols;

· alkali metal and alkaline earth metal salts of C8-C24 alfa-olefin sulfonate;

• polyelectrolytes, such as lignosulfonates, condensates of naphthalenesulfonate and formaldehyde, polystyrenesulfonate or sulfonated unsaturated or aromatic polymers;

• anionic esters of alkylpolyglycosides, such as alkylpolyglucoside sulfosuccinate or citrate; • salts of alkyl sulfosuccinic acid, which are esterified once or twice with linear, or branched aliphatic, cycloaliphatic and/or aromatic alcohols, or sulfosuccinates which are esterified once or twice with (poly)alkylene oxide adducts of alcohols.

Examples of suitable cationic and ampholytic surfactants are quaternary ammonium salts, alkyl amino acids, and betaine or imidazoline amphotensides.

In a preferred embodiment, the surfactant is an anionic surfactant.

Preferred anionic surfactants are, for example, salts of alkyl sulfosuccinic acids, such as sodium dioctyl sulfosuccinate, and anionic esters of alkylpolyglycosides, in particular alkylpolyglucoside citrate.

According to another embodiment of the invention, the derivatized tamarind gum is provided in a composition free from synthetic surfactants comprising from 10 to 50 wt%, preferably from 10 to 40 wt%, more preferably from 12 to 30 wt%, of said derivatized tamarind gum, that is diluted before application onto the soil .

Optionally, the composition also includes additives commonly used in the field, such as anti-drift agents, corrosion inhibitors, microbial inhibitors, pH adjusters, anti-foam agents and mixture thereof.

In a particularly preferred embodiment the composition of the invention is in powder form.

In another particularly preferred embodiment, the composition of the invention is an aqueous composition comprising :

a) from 10 to 40 % by weight (wt %) of a derivatized tamarind gum; b) from 0.2 to 20 % by weight of at least a surfactant;

c) from 0 to 50 % by weight of a compatibilizer.

Typically, the aqueous composition comprises at least 30% by weight, preferably from 40 to 80% by weight, of water. Preferably, in the aqueous composition of the present disclosure the compatibilizer is chosen among glycerol and sodium xylene sulfonate. Preferably the compatibilizer is glycerol.

The aqueous compositions of the invention preferably have a Brookfield® viscosity comprised between 10 and 5000 mPa*s, preferably between 100 and 2500 mPa*s.

The composition of the invention can be prepared by simply mixing the various components and the other optional additives.

The derivatized tamarind gums of the invention (and the compositions thereof) can be applied as such or they can be dissolved/suspended/diluted just before use with water to provide ready-to-use moisturizing agents.

In a preferred embodiment, the derivatized tamarind is applied onto the soil after dilution in water in the form of an aqueous solution.

Conveniently, the disclosed moisturizing agents may also contain further components, such as agrochemical active ingredients, stabilizers, adjuvants, pH adjusters, anti-foam agents, plant nutrients including fertilizers and heavy metals, and the like. Preferred further components are plant nutrients.

The ready-to-use moisturizing agents of the present invention can comprise from about 0.01 to about 8 wt.%, preferably from about 1 to about 4 wt.%, of further components.

Examples of suitable fertilizers include sources of nitrogen, of phosphorous, of potassium and mixture thereof. Non-limiting examples of sources of available nitrogen include, urea, ammonium nitrate, potassium nitrate, and mixtures thereof. Examples of sources of available phosphorous include ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen monophosphate, sodium phosphate, disodium phosphate, and mixtures thereof. Available sources of potassium include any suitable water soluble potassium salt. Non-limiting examples of sources of heavy metals include chelated iron (for example with EDTA), manganese, and zinc.

The disclosed derivatized tamarind gums can be applied to any kind of soil but they are particularly suited to: sandy soil, loamy soil, sandy clay loam, sandy clay, sandy as defined in "Soil Survey Manual" United States Dept. of Agric. U. S. Government Printing Office, Washington, D. C. 20402. (CHAPTER 3).

The application can be performed in a number of ways, for example by spraying, sprinkling or broadcasting on the soil surface, preferably before working of the soil, or by mulching, plowing, disking and the like, particularly when the soil conditioner is applied as a dry solid.

EXAMPLES

Characterization Methods

The Brookfield® RV viscosity (BRK Viscosity) in mPa*s was measured on a 4.0 % by weight solution in water at 20 °C and 20 rpm, unless otherwise specified.

The cationic degree of substitution (DS_cat), the molar substitution (MS) and anionic degree of substitution (DS_an) were determined by ^-NMR.

The dry matter content in % by weight was determined using a MJ33 Moisture Analyzer from Mettler-Toledo, set at temperature of 110 °C and on automatic switch-off.

The surface tension was determined using a force tensiometer (Sigma 70, from Nordtest s.r.l., Italy).

The weight average molecular weight (M_w) in dalton was determined by gel permeation chromatography using a Perkin Elmer Series 200 Pump, an Ultrahydrogel guard column, an Ultrahydrogel Linear column (Waters) and an Evaporative Light Scattering Detector ELSD 3300 (Alltech). The mobile phase was a 0.1 M triethanol amine/0.1 M acetic acid water solution at a flow rate of 0.8 ml/min. A pullulan standard kit (molecular weight range : 432 - 1,330,000 Dalton) was used for the calibration of the system.

The calculations were performed by the chromatographic software SW TurboSEC 6.2.1.0.104: 0104 with a Universal Calibration method . The following values of the Mark-Houwink constants K and a were assigned :

Examples 1-13

Table 1 reports the characteristics of the derivatized tamarind gums according to the invention and those of the underivatized tamarind gum and the derivatized polysaccharides/gums used as comparative Examples.

Examples 1, 3 and 5 are aqueous solutions of depolymerized derivatized tamarind gums; Example 2, 4 and 6 are derivatized tamarind gums in powder form.

Comparative Examples 7 and 9-12 are aqueous solutions of depolymerized derivatized polysaccharides/gums; comparative Examples 8 and 13 are products in powder form.

Table 1

576

6 Cat. Tamarind - - 0.25 95 654000

(4%w/w)

7* HP Guar Acid 0.35 - 28.4 2000 -

1800

8* NaCM Cellulose - - 0.66 95 - (1% w/w)

g* NaCM Cellulose Enzyme - 0.70 37.6 1100 -

10* NaCM Guar Acid - 0.16 32.2 3750 -

11* Cat. Guar Acid - 0.14 30.4 2040 -

12* Cat. HP Guar Acid 0.61 0.12 29.6 2230 -

18400

13* Tamarind Gum - - - 95.4 - (5% w/w)

* Comparative

** HP = hydroxypropyl, NaCM = sodium carboxymethyl, Cat. = hydroxypropyl trimonium chloride

After depolymerization, the solutions of Examples 1, 3, 5, 7 and 10-12 were neutralized with KOH.

Surface tension of polymeric solutions

The ability of aqueous solutions of polymers, such as the derivatized tamarind gums of the invention, to permeate easily trough the capillaries of the soil without the help of a surfactants can be evaluated by determining the surface tension of these solutions.

Table 2 reports the values of the surface tension in mN/m at 25 °C of 0.1% solutions, as dry matter, in water.

Table 2

5 51.18

6 46.48

7* 58.98

8* 70.11

g* 71.80

10* 62.94

11* 58.23

13* 57.97

Comparative

The results shows that aqueous solutions of the derivatized tamarind gums of the invention have lower surface tension than underivatized tamarind gums and to derivatized gums/polysaccharides of the prior art, such as carboxymethyl cellulose and cationic guar. This demostrates that solutions of the derivatized tamarind gums of the invention are able to permeate more easily trough the capillaries of soil and that they do not need the presence of a surfactants.

Application Tests

Water Evaporation

Polymers in solution

80 grams of quartz sand (Knauf s.r.l ., Italy) were carefully packed in a petri dish (8.7 cm i.d.) to obtain a bulk density of about 0.2 g/cm³. 16 grams of aqueous polymer solution or water (blank) were homogeneously distributed onto the sand .

The Petri dishes were then placed for 6 h in an incubator (Genviro 30 L AG-System, Fratelli Gall i G&P, Italy) set at 25 °C and 30 % humidity. The superficial evaporation was evaluated as weight loss over the time. Table 3 reports the results, as % weight of water retained into the sand, compared to the value of the blank (Δ WR %). Table 3

Comparative

The values of WR % demonstrate the superior water retention properties of the derivatized tamarind gums of the invention.

Polymers in powder form

The polymers in powder form were tested in a slightly different way.

In order to avoid the accumulation of water on the surface, the sand was packed in the petri dish with a bulk density of about 0.2 g/cm³ in two layers:

• a lower layer consisting of 60 g of sand mixed with 0.16 g of polymer powder;

• an upper layer consisting of 20 g of sand.

16 grams of water were then distributed homogeneously onto the sand . The upper layer allows the water to flow freely under the surface to the layer with the polymer powder.

A blank test was performed using 80 g of pure sand without any polymer. The Petri dishes were conditioned in the incubator set at 25 °C and 30 % humidity for 6 h.

The superficial evaporation was evaluated as weight loss over the time. The results are reported in Table 4, as weight % of water remained into the soil compared to the value of the blank (Δ WR %). Table 4

Comparative

Water retention test

A moisture probe (Waterscout Moisture Sensor, from Spectrum Technologies Inc., USA) was placed vertically in the middle of a column (5,2 cm i.d.) containing 250 grams of quartz sand (Knauf s.r.l., Italy) and buried at a depth of 6.5 cm, so that the whole sensor was covered with sand . The sand was then were carefully packed to obtain a bulk density of about 0.4 g/cm³.

50 ml_ of a 0.5 % wt, as dry matter, aqueous solutions of the polymers were dosed on the top of the column over a 52 min period using a peristaltic pump (Pump P-l, from GE Healthcare Life Sciences, USA).

The volumetric water content (VWC%) of the sand was recorded using a Watchdog 1400 Micro Station (Spectrum Technologies Inc., USA).

Table 5 reports the VWC% difference between the polymer solutions and deionized water (Δ VWC%) after 52 and 300 min.

Table 5

10* 4.6 3.9

11* 8.4 7.1

12* 3.3 3.2

13* 2.1 3.1

Comparative

The data show that the derivatized tamarind gums of the invention are able to retain more water the derivatized polysaccharides of the prior art.

Infiltration capability

350 grams of quartzifer sand (Knauf s.r.l ., Italy) were carefully packed in a glass column (6.8 cm i.d .) to reach the height of 7.0 cm.

Two moisture probes (Waterscout Moisture Sensor, from Spectrum Technologies Inc.. USA) were placed horizontally in two slit on the side of the column : one about 3 cm below the top of sand (Probe 1) and the other about 1 cm above the bottom of the sand (Probe 2).

40 ml_ of a 0.5 % wt, as dry matter, aqueous solutions of the polymers were poured on the top of the columns.

The volumetric water content (VWC %) obtained from the two probe was recorded using a Watchdog 1400 Micro Station.

Table 6 reports the VWC % soon after pouring the solutions (0 h) and after 6 hours (6 h).

Table 6

1 42.3 36.6

g*

2 9.9 16.2

1 25.1 19.3

10*

2 9.7 15.8

Comparative

The reported data demonstrate that the aqueous solutions of derivatized tamarind gums of the invention are able to flow more easily trough the particle of sand (from probe 1 to probe 2) without the addition of a surfactant. On the contrary, the polymers of the prior art keep the largest part of the water on the top of the column of sand (VWC % of probe 1 higher than VWC % of probe 2 also after 6 hours).

Claims

1) A method, for improving the water retention of soil, comprising the application onto the soil of from 0.05 to 5.0 kg/ha of a derivatized tamarind gum, selected in the group consisting of hydroxyalkyl tamarind, carboxyalkyl tamarind, cationic tamarind and hydrophobically modified tamarind, with the proviso that the carboxyalkyl tamarind are in the form of a salt of alkali metal ions.

2) The method of claim 1), comprising the application onto said soil of from 0.1 to 3.5 kg/ha of said derivatized tamarind gum.

3) The method of claim 2), wherein said derivatized tamarind gum is a hydroxyalkyl tamarind with a hydroxyalkyl molar substitution (MS) comprised between 0.1 and 3.0.

4) The method of claim 2), wherein said derivatized tamarind gum is a carboxyalkyl tamarind with a degree of carboxyalkyl substitution (DS_an) comprised between 0.01 and 1.2.

5) The method of claim 2), wherein said derivatized tamarind gum is a cationic tamarind with a cationic degree of substitution (DS_cat) comprised between 0.01 and 1.0.

6) The method of claim 1), wherein said derivatized tamarind gum is a depolymerized derivatized tamarind gum, which has been depolymerized by using suitable chemicals or cellulase enzymes.

7) The method of claim 1), wherein said derivatized tamarind is applied after dilution in water in the form of an aqueous solution.

8) The method of claim 1), wherein said derivatized tamarind is applied after dilution in water of a composition comprising :

a) from 10 to 50 % by weight (wt%) of the derivatized tamarind gum; b) from 0.2 to 30 % by weight of at least a surfactant.

9) The method of claim 8), wherein the surfactant b) is selected from the group consisting of salts of alkyl sulfosuccinic acids and anionic esters of alkylpolyglycosides. 10) The method of claim 1), wherein said derivatized tamarind is applied after dilution in water of a composition free of synthetic surfactant and comprising from 10 to 50 % wt% of the derivatized tamarind gum.

11) The method of any of the claims from 1) to 10) wherein the derivatized tamarind is non-crosslinked .