Effect of Polysaccharides, Clay Dispersion, and Impact Energy on Water Infiltration
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Effect of Polysaccharides, Clay Dispersion, and Impact Energy on Water InfiltrationM. Ben-Hur* and J. Letey
ABSTRACTEffects of clay dispersion, impact energy of water drops, and
chemical amendments on crust formation and infiltration rate (IR)of Haplic Durixeralf soil were studied using a sprinkler infiltro-meter. The soil was subjected to two impact energies, high energy= 240 J m 2 h ' and low energy = 0, and to three waters: (i) distilledwater [DW, electrical conductivity (EC) < 0.05 dS nr'], (ii) salinewater (SW, EC = 5.0 dS m~'), and (iii) regular water (RW, EC =1.0 dS m ') The chemical amendments, polysaccharides, guar de-rivatives were supplied with the DW and RW and with high impactenergy. Crust formation by the impact energy was found as a dom-inant factor in the IR reduction. This factor reduced the total soilinfiltration capacity by more than 40%. Conversely, clay dispersionin the soil surface reduced the total soil infiltration capacity by 24%.Likewise, it was found that clay dispersion in the soil surface de-creased the hydraulic conductivity of the crust and sharply increasedits hydraulic resistance. The polymers had an amendatory effect onthe IR. The polymers apparently adsorbed on the particle surfacesand acted as a cementing material holding primary particles togetheragainst the destructive forces of the water drops. The order of themaximum effect of the chemical amendments (0.01 kg m'3), thatwere supplied in DW, on the maintenance of IR was: high chargecationic polymer (HCCP) > low charge cationic polymer (LCCP) nonionic polymer > anionic polymer (had no effect). A concen-tration of 0.01 kg m-3 of HCCP and LCCP in RW prevented crustformation and preserved the high initial IR of the soil throughoutthe water application period. The HCCP and LCCP under sprinkledDW and RW conditions apparently adsorbed at the soil surface anddid not move with the water into the soil layer.
Low WATER INFILTRATION resulting in runoff, ero-sion, inefficient water use, and plant injury dueto water ponding is a significant problem in some ir-rigated lands. For example, the infiltration rates of over1 million ha of irrigated land on the east side of theSan Joaquin Valley of California are reduced duringthe irrigation season to rates as low as 1 mm h-1 (Os-ter and Singer, 1984). Low infiltration rates are par-ticularly acute for irrigation by systems that have ahigh instantaneous rate of water application like amoving sprinkler (Gilley and Mielke, 1980).
The reduction of the infiltration rate is caused mainlyby the formation of crust on the soil surface and/orby the reduction of the hydraulic conductivity of thebulk soil (Ben-Hur et al., 1987; Shainberg and Letey,1984).
Surface crusts are thin and characterized by greaterdensity, higher strength, finer pores, and lower satu-rated conductivity than the underlying soil (Gal et al.,1984; Mclntyre, 1958). Impact energy of the waterdrops and water surface stream break down the sur-face aggregates, compact the upper soil layer, and formthe crust (Morin and Benyamini, 1977). In additionDep. of Soil and Environmental Sciences, Univ. of California, Riv-erside, CA 92521. Research was supported by the Univ. of Califor-nia Kearney Foundation of Soil Science. Received 1 Apr. 1988.'Corresponding author and visiting soil scientist from AgriculturalResearch Organization (ARO), Volcani Center, Israel.Published in Soil Sci. Soc. Am. J. 53:233-238 (1989).
to physical breakdown of the soil aggregates, physical-chemical dispersion of soil clays can cause clogging ofthe pores immediately beneath the surface, which isfrequently referred to as the "washed in" zone (Agassiet al., 1981; Kazman et al., 1983). On the other hand,swelling and dispersion of clay from aggregates thatmigrate and lodge in pore spaces greatly reduce thehydraulic conductivity of the bulk soil (McNeal andColeman, 1966; Park and O'Connor, 1980; Shainberget al., 1981a,b). Felhendler et al. (1974) found thatwater with intermediate sodium adsorption ratio(SAR) values of 5 to 10 and a low solution electrolyteconcentration caused soil clay particle dispersion andreduced the hydraulic conductivity to near zero.
Treatment of soils with chemical amendments toimprove or maintain soil structure and aggregate sta-bility may be one means of maintaining high waterinfiltration. Polymers have been shown to be effectivein increasing hydraulic conductivity and porosity, im-proving water-holding capacity (Shanmuganathan andOades, 1982), and reducing erosion and weakeningcrust strength (Wood and Oster, 1985). The effects ofpolymers as soil conditioners were reviewed by Harriset al. (1966).
However, most of the initial studies with polymersdealt with applying copious amounts of polymers eitherdry or by spraying and then mixing to create soil ag-gregates. Consequently, the polymers used for agri-culture were too expensive and not economically fea-sible. Therefore, it is important to study potentiallyactive polymers that can be easily applied (such aswith irrigation water) at relatively low amounts andyet have a significant positive effect on the soil phys-ical properties.
The objectives of this study were: (i) to study theeffects of clay dispersion and impact energy of the waterdrops on crust formation and water infiltration; (ii) todetermine the effect of low concentration of some typesof guar derivatives in irrigation water on the infiltra-tion rates; and (iii) to study the interaction betweenthe polymers and water quality in crust formation.
MATERIALS AND METHODSThe
234 SOIL SCI. SOC. AM. J., VOL. 53, JANUARY-FEBRUARY 1989
Table 1. Some physical and chemical properties of Arlington sandyloam (Riverside County, CA).
cmolc kg" '9.5 18.0
ESP CaCO3 M V Q+F
2.0 t4 tr 72 14
f Composition of clay fraction where the following minerals are identified bythe symbols: M = montmorillonite, Q = quartz, V = vermiculite, F =feldspar, and K = kaolinite.|tr = trace amount, < 0.1%.
mechanical parameters of the applied sprinkler water were:instantaneous application rate of 30 mm h~', water dropaverage diameter of 3.5 mm, water drop velocity of 4.0 ms~', and total kinetic energy of 240 J m~2 h~'.
The soil was first saturated from the bottom with tap water[electrical conductivity (EC) = 0.7 dS m~'] and then re-ceived 50 mm of various treated waters by the SI. The vol-umes of water percolating through the soil were recorded foreach 2.5 mm of water application to compute infiltrationrate. The average clay concentration in the total collectedeffluent was determined by gravimetric procedure.
Three waters were synthesized and applied in the sprin-kler infiltrometer: (i) distilled water (DW) with EC < 0.05dS m~' that represented snow water; (ii) saline water (SW)with EC of 5.0 dS m~' that represented saline irrigation water;(iii) regular water (RW) with EC of 1.0 dS m"' that repre-sented the common water in arid and semiarid regions. TheSAR of the RW and SW was 2.0, and were prepared bymixing NaCl and CaCl2 in appropriate amounts. The DWand the SW were applied with high and low impact energyof water drops (240 J rrr2 h~' and 0). The low impact energywas obtained by placing two fiberglass sheets over the soilsurface at a 0.5-cm height. The RW and following polymerstreatments were carried out under high impact energy con-ditions only.
The amendatory compounds tested were derivatized guarprovided by Celanese Corp. (Louisville, KY). The molecularweight of the compounds is relatively low (200 000-2 mil-lion) and they are soluble in water. The polymer compoundswere either nonionic, anionic, or cationic with differing chargedensity. The type and density of the charge of the com-pounds were determined by the types and the amounts ofthe substitutional groups. Schematic structure of the com-pounds regarding their charge is given in Fig. 1.
A source solution of 0.5 kg m~3 of each polymer was pre-pared in DW and appropriate amounts of these solutionswere added to the appropriate water to be tested by the ISto form concentrations of 0.0025, 0.005, 0.01, and 0.02 kgm-3.
RESULTS AND DISCUSSIONThe best fit curves obtained from least squares anal-
ysis of the infiltration rate (IR) values as a functionof water application depth for DW and SW for bothcovered and uncovered soil and the R2 of the regres-sion are presented in Fig. 2 and Table 2, respectively.The IR of the covered soil that was subjected to SWwas maintained at the initial infiltration value duringthe entire run. Coverings and saline water have beenshown to prevent clay dispersion (Shainberg and Le-tey, 1984) and the physical breakdown of the soil ag-gregates (Morin and Benyamini, 1977). Consequently,in this treatment a crust was not formed, the hydraulicconductivity of the soil layer was not likely reducedthus maintaining the IR. When the covered soil was
H(R),H H H H
HYDROXYPROPYL GUAR (NONIONIC)
H H H H H / HCH2COO~Na+
CHgOHQ = Quaternaryammonium group
H H H H H ' HCATIONIC GUAR
Fig. 1. Schematic structure of the polymers studied.
subjected to DW, the IR decreased with increasingamount of the water application. Likewise, the aver-age value of the clay concentration in the total col-lected effluent was 0.29 mg mL~' in this treatmentcompared to 0 in the SW treatment (Table 2). Eventhough the covering prevented crust formation fromimpact (a visual observation after the run indicatedthat the surface aggregates did not break down), leach-ing the soil layer with DW caused clay dispersion, mi-gration, and relodgment in the pore spaces that re-duced the hydraulic conductivit