Effect of Synthetic Conditioners on Soil Water Retention, Hydraulic Conductivity, Porosity, and Aggregation1
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DIVISION S-6SOIL AND WATER MANAGEMENTAND CONSERVATION
Effect of Synthetic Conditioners on Soil Water Retention, Hydraulic Conductivity,Porosity, and Aggregation1
M. N. NIMAH, J. RYAN, AND M. A. CHAUDHRY2
ABSTRACTRecent attention has been focused on the use of synthetic soil con-
ditioners in the modification of soil water relationships especially in aridregions. Soils of extremes in textureeither sands or clayspresentproblems in this regard. In this laboratory study, Hygromull (a ureaformaldehyde) and Agrosil LR and Agrosil S (amorphous sodium hy-drosilicates) were evaluated on soils of different textures. Available watercontent was increased by Hygromull and Agrosil LR. Saturated hy-draulic conductivity of the clay soils was improved by Hygromull, whilethat of the sandy soil was reduced by Agrosil LR. Hygromull increasedporosity of all soils but, unlike Agrosil LR, had no effect on aggregation.In contrast, Agrosil S had no effect on any property studied. Notwith-standing the attributes of these conditioners, their acceptance in com-mercial farming in dry regions will depend on the outcome of field trialsand economic considerations.
Additional Index Words: sandy soils, clay soils, permeability, Hy-romull, Agrosil, soil amendments, soil conditioners
Nimah, M.N., J. Ryan, and M.A. Chaudhry. 1983. Effect of syntheticconditioners on soil water retention, hydraulic conductivity, porosity,and aggregation. Soil Sci. Soc. Am. J. 47:742-745.
1 Contribution from the Soils, Irrigation and Mechanization Dep.,
Faculty of Agricultural and Food Sciences, American University ofBeirut, Beirut, Lebanon. Journal no. 575 B. Received 23 Apr. 1982.Approved 26 Oct. 1982.?
Associate Professors and Graduate Student, respectively.
SOIL CONDITIONING implies improvement of the soil'sphysical properties, thus permitting more effectiveutilization of soil and water resources. In recent years,considerable emphasis has been placed on the use of awide array of chemicals purporting to favorably influencesoil properties. Some materials are produced directly forsuch purposes, while others are by-products of industrialprocesses. A relatively recent review of the subject in-cludes materials used for soil conditioning, their mode ofaction, their use in soil and water management, and theirglobal use extent, both in agricultural and nonagricul-tural purposes (Gardner and Moldenhauer, 1975). Syn-thetic soil conditioners can be classified as soluble organicpolymers, emulsions, silicates, and foams.
Soluble materials undergo physico-chemical reactionswith soil constituents especially the clay fraction. Upondrying, an insoluble irreversible matrix is formed whichgenerally results in improved aggregation, porosity, andhydraulic conductivity (Schamp et al., 1975). Thus, suchmaterials are used to stabilize highway banks and con-struction sites, and to combat soil crusting, which impedesgermination, and both wind and water erosion. Othermaterials do not react with soil constituents but exert aneffect through modification of soil texture and by increas-ing soil water retention.
NIMAH ET AL.: EFFECT OF SYNTHETIC CONDITIONERS ON SOIL WATER, POROSITY, & AGGREGATION 743
Soil conditioners have potential importance in the aridand semi-arid regions of the world where there is a de-veloping awareness of the implications of soil erosion andinefficient water use. Such materials can favorably mod-ify soil water relationships especially retention and trans-mission (Hartman et al., 1976). Chemical soil condition-ers vary from well-defined inorganic salts and syntheticpolymers to products whose properties are less clearlyunderstood. While some studies have demonstrated pos-itive effects of soil conditioners, i.e., marked increases insoil water diffusivity with Krillium and polyvinyl alcohol(Kijne, 1967), others have not. For instance, in green-house and field studies with sandy soils cropped to turf-grass, McGuire et al. (1978) found that none of the con-ditioners studied, i.e., two bituminous emulsions, fivepolyacrylamides (PAM), and one polyvinyl alcohol(PVA), beneficially affected soil physical properties, cat-ion exchange capacity (CEC), or any turf grass param-eter. However, other studies such as that of Bolton et al.(1955) showed that soil conditioners (hydrolyzed poly-acrylonitrile and a modified vinyl acetate maleic acidcompound) improved aggregation and both total andnoncapillary pore space in a clay soil but had no effecton crop yield under field conditions.
While most studies of soil conditioners have dealt withsoluble polymers and emulsions, the literature on silicatesand foams is scant. Agrosil and Hygromull are examplesof such materials. Buring and Prun (1974) showed thatthe silicate Agrosil LR increased water-holding capacityand decreased water percolation rate in sandy soils dueto a decrease in average pore size. In contrast, the find-ings of Khoury et al. (1978) showed that it increasedpore size. Similarly; under semiarid conditions, improvedcrop growth was reported with Agrosil LR and the acidicfoamAgrosil S (Buring and Prun, 1974),whereas, inthe field trials described by Khoury et al. (1978), nopositive effect was subsequently shown. In studies withthe foam materialHygromullRasp (1972) showedthat it improved the water-holding capacity, increasedporosity, and reduced bulk density of a sandy and a loamsoil. Buchner et al. (1969) similarly reported improvedwater-holding capacity in light-textured soils and aera-tion in heavy clay soils. However, the observation byKhoury et al. (1978) that Hygromull increased pore di-ameter and reduced available water in a clay soil ques-tions the validity of these findings.
Because of the dearth of published information on sil-icate and foam-type synthetic conditioners, the unrecon-ciled reports dealing with Agrosil and Hygromull, andthe lack of integration between measured parameters inreported studies, an investigation was undertaken withthese materials to determine their influence on sandy andclay soil water retention, hydraulic conductivity, poros-ity, and aggregation.
MATERIALS AND METHODSSoils and Soil Conditioners
Soil samples were selected from three locations in Lebanon:Leba'a in the south; Furzol in the central Beka'a valley; andSheia'h near Beirut on the coast; some physical and chemicalproperties are given in Table 1. Samples were air-dried andpassed through a 2-mm sieve for this study.
The synthetic soil conditioners (produced by BASF, SpartRII-VA2, 6700 Ludwigshafen, Rhein, Germany) were Hygro-
Table 1Some physical and chemical characteristics of the soils.Soil Organiclocation Classification Sand Silt Clay CaCO3 carbon pH
80.0 2.8 17.2 0.0 0.3 8.0Sheia'h ArentLeba'a Rendollic
xerorthent 17.1 28.2 54.7 75.2 0.9 8.0Furzol Vertic
xerochrept 12.4 26.0 61.6 38.1 0.9 8.2
mull and two forms of Agrosil. Hygromull is a ureaformalde-hyde foam (flakes) with 30% C and 30% N and a bulk densityof 0.035 g/cm3. By virtue of its porous structure, Hygromull isclaimed to absorb 50 and 70% water on a volume basis whenincorporated into the soil under normal field conditions (Prunand Drach, 1977). Though water is absorbed slowly by thismaterial, it is believed to be released uniformly to the plant. Itis recommended for increasing water-holding capacity of sandysoils and improving aeration of clay soils. Agrosil LR is anamorphous sodium silicate having 45% Sio2, 8.7% P, a pH of7, and a bulk density of 0.76 g/cm3. Agrosil S contains 36%SiO2, 44% P, and 6% S; has a pH of 3.0 to 3.5; and a bulkdensity of 0.87 g/cm3. Upon dissolution in water, Agrosil formsa mixture of gels and sols (Prun, 1974; Buring and Prun, 1974).The larger moleculed silicate gels are honeycombed with cap-illary pores which retain water. Precipitation or formation ofgels influences pore size distribution and thus permeability.When Agrosil S is used in calcareous soils, an added effect inreducing soil compaction is postulated due to the evolution ofCC
744 SOIL SCI. SOC. AM. J., VOL. 47, 1983
-15 -10 -5 -2 -1Matric potential (bars)
Fig. 1Water retention as a function of matric potential after six wet-ting-drying cycles by the sandy Sbeia'h soil previously treated withsoil conditioners.
Soil Physical MeasurementsAfter 48 h from the finalpermeability measurement, bulk density was determined by thecore method (Blake, 1965) while porosity was calculated fromthe measured bulk density, assuming particle density of 2.65g/cm3. Water-stable aggregates were determined by the ag-gregate-size distribution with wet sieving (Richards, 1954).
RESULTS AND DISCUSSIONAvailable water and permeability data for the three
soils treated with the conditioners Hygromull, AgrosilLR, or Agrosil S are presented in Table 2. Interpretationof the available water data is facilitated by depictingwater content after six wetting-drying cycles at the en-tire range of matric potentials considered for the Sheia'h(Fig. 1), Leba'a (Fig. 2), and Furzol (Fig. 3) soils.
Available water was influenced differentially by thesoil conditioners depending on soil properties, notablytexture. Hygromull increased water retention by about125% in the sandy Sheia'h soil and about 25 to 30% forthe clay soilsLeba'a and Furzol. However, this effectwas not observed with the sandy soil at the first deter-
Table 2Influence of soil conditioners on available water andpermeability of three soils after varying
No. of wetting-drying cycles
ControlHygromullAgrosil LRAgrosil S
2 4 6
- % Sheia'h*
4.0 4.39.2 9.76.0 6.4