Effects of bentonite on water infiltration in a loamy sand soil

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  • This article was downloaded by: [Temple University Libraries]On: 20 November 2014, At: 09:37Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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    Effects of bentonite on waterinfiltration in a loamy sand soilRezvan Talebnezhad a & Ali Reza Sepaskhah aa Irrigation Department , Shiraz University , Shiraz , IranAccepted author version posted online: 10 Jul 2012.Publishedonline: 06 Aug 2012.

    To cite this article: Rezvan Talebnezhad & Ali Reza Sepaskhah (2013) Effects of bentonite on waterinfiltration in a loamy sand soil, Archives of Agronomy and Soil Science, 59:10, 1409-1418, DOI:10.1080/03650340.2012.708926

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  • Effects of bentonite on water infiltration in a loamy sand soil

    Rezvan Talebnezhad and Ali Reza Sepaskhah*

    Irrigation Department, Shiraz University, Shiraz, Iran

    (Received 26 March 2012; final version received 28 June 2012)

    Water loss as deep percolation is considerable in furrow irrigation in light soilsdue to the high infiltration rate. Application of soil conditioners such as bentonitereduces the infiltration rate and improves irrigation application efficiency (Ea) inthese soils. The effects of bentonite application rates (BAR) of 0, 2, 4 and 6 g L71

    on infiltration of a loamy sand soil were determined in a soil column in thelaboratory. The exponent of the Kostiakov infiltration equation was notinfluenced by BAR. Maximum reduction in infiltration equation coefficient andfinal infiltration rate (if) occurred with 2 g bentonite L

    71 and this reduction waslower on increasing BAR from 2 to 4 and 4 to 6 g L71 compared with control.The effect of 2 g L71 BAR on infiltration and its effect on the design of furrowirrigation in a field with a loamy sand soil indicated that in the first irrigation afterfield ploughing and seed planting, longer furrow length, lower deep percolationand higher Ea are obtained.

    Keywords: infiltration rate; soil conditioners; furrow irrigation; irrigationapplication efficiency

    Introduction

    When water resources are scarce, water loss should be prevented. In this regard,irrigation application efficiency (Ea), especially in light-textured soils, and surfaceirrigation should be improved. In furrow irrigation in light soils, deep percolation ishigh due to the high infiltration rate (IR) and saturated hydraulic conductivity (Ks).Therefore, a short furrow length, which results in this condition, is not desirable infurrow irrigation design and nor is the use of farm machinery with a low Ea.

    The design and efficiency of surface irrigation are dependent on the infiltrationequation (Walker and Skogerboe 1987). In surface irrigation, the inflow rate shouldbe greater than the infiltration rate for water advancing along the border or furrow.The water advance rate in surface irrigation in light-textured soils, especially in thefirst irrigation after field ploughing and seed planting, is slow due to the highinfiltration rate. Therefore, the application of soil conditioners that reduce theinfiltration rate of light-textured soils may result in a higher water advance rate.With the application of soil conditioners, the coefficient of infiltration equation ischanged such that there is an increase in furrow length and Ea.

    Soil hydraulic properties are dependent on the particle size distribution, soilstructure, bulk density, organic matter and clay types (Mingorance et al. 2007).

    *Corresponding author. Email: sepas@shirazu.ac.ir

    2013 Taylor & Francis

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  • Therefore, soil conditioners can be used to improve these properties and decrease theinfiltration rate (Ibrahim-Saeedi and Sepaskhah 2011; Gholizadeh-Sarabi andSepaskhah 2012).

    The effect of a gel material (Jalma) on some physical properties of light-texturedsoils was studied by Al-Darby (1996). Al-Darby proposed that application of 0.4%Jalma can decrease Ks and deep percolation by a considerable amount. Lentz (2003)mixed polyacryamide (PAM) into the soil surface layer at a rate of 45 kg ha71 andmeasured the infiltration rate. Lentz showed a greater reduction in infiltration rate ina silt loam compared with loamy sand soil. Application of PAM also reducedseepage from the irrigation canal (Lentz and Freeborn 2007). Young et al. (2009)studied the effect of PAM on Ks of sandy soils and indicated that mixing PAM withthe soil surface layer resulted in a reduction in Ks.

    Bentonite contains smectite clay with 2:1 layers with a high specific surface areathat is expandable and absorbs a great amount of water. Chalermyanont andArrykul (2005) reported that a mixture of sand and bentonite of 5% reduced Ks byfour times compared with sand. An increase in the amount of bentonite in thebentonitesand mixture did not decrease Ks further. Furthermore, Komine (2004)studied the effect of different mixtures of sand and bentonite (10, 20 and 30% ofbentonite) on Ks and expansion force. By increasing the percent of bentonite theexpansion force increased and resulted in smaller effective pores and Ks. Ibrahim-Saeedi and Sepaskhah (2011) studied the effect of irrigation water with differentbentonite concentrations on Ks of a loamy sand soil. Their results indicated thatbentonite concentration of 0.2% reduced Ks of the soil surface layer by 56% and theKs of the subsurface layer by 30%. Therefore, it was indicated that bentoniteapplication was more effective at Ks reduction in surface soil. Ebina et al. (2004) andYeo et al. (2005) reported that Ks of a mixture of sand and Na-bentonite was reducedto 1.0 6 1079 cm s71 and this reduction was lower for Ca-bentonite (Sivapullaiahet al. 2000; Sallfors and Oberg-Hogsta 2002; Abichou et al. 2002; Lee andShackelford 2005). Ameta and Wayal (2008) found that the lowest Ks value occurredin a 10% mixture of bentonite and sand.

    According to the study of Ibrahim-Saeedi and Sepaskhah (2011), a bentonitemixture with water can reduce Ks of the soil surface. Application of this findingmight be used in water-loss reduction in irrigation channel construction in light soiltextures. However, the effect of a mixture of bentonite and water on the infiltrationrate and the coefficients of infiltration equation has not been investigated. Thefinding of such an investigation could be applied in surface irrigation design toimprove furrow length and water application efficiency in light-textured soils. Theobjectives of this study were to investigate: (1) the effects of different concentrationsof bentonite in water (0, 2, 4, and 6 g L71) on coefficients of the Kostiakovinfiltration equation in a loamy sand soil in a soil column in the laboratory; and (2)the effects of a modified infiltration equation on the design of furrow irrigation.

    Material and methods

    In this study, a loamy sand soil was used. The physical properties of the soil areshown in Table 1. Sodium bentonite was used and the chemical properties ofbentonite are presented in Table 2. The effect of bentonite on infiltration wasmeasured in soil columns. The column was made of a polyvinyl chloride (PVC) tubeof 85 mm i.d. and 470 mm height. A gravel filter with a thickness of 75 mm was

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  • placed in the bottom of the soil column. The bottom ends of these cylinders wereclosed by a layer of foam and equipped with a drain tube connected to the gravellayer (Figure 1). These columns were filled with soil to a height of 300 mm. Toprepare the soil columns, air-dried soil samples were passed through a large 2-mmsieve and a predetermined weight of air-dried soil was placed in the PVC column.Soil initial water content was determined by gravimetric method (Table 1). Soil waspoured into the column using a funnel with long stem to prevent non-uniform soilpacking. Then based on the weight and volume of soil in the column, the apparentbulk density of soil was determined (Table 1). The internal surface of the cylinderwall was lubricated with grease to prevent preferential lateral water flow in thecolumn. The experimental soil column set-up is showed in Figure 1.

    The chemical composition of the fresh water is shown in Table 3. Differentbentonitewater mixtures were used with bentonite concentrations of 0, 2, 4 and6 g L71 in fresh water. Although the concentration of the bentonitewater mixtureseems low, bentonite is accumulated by continuous application in a thin near-surfacelayer of soil (*0.05 m) and a bentonitesoil mixture can reach *30% at aconcentration of *6 g L71.

    The infiltration experiment was initiated by flowing water from the bentonitesolution reservoir to the soil surface and a height of 10 mm of water was establishedon the soil surface. Water was added to the soil column and the amounts of infiltratedwater at different elapsed times were determined by measuring the increased weight ofthe soil column using an electrical balance with a precision of+0.001 g (Figure 1). Toprevent bentonite sedimentation in the solution, an electrical mixer was used in thesolution reservoir. The infiltration experiment was continued until the infiltratedwater front reached the bottom of the soil column. The outflow of infiltrated waterwas measured. These measurements continued until steady-state infiltration wasreached. The steady-state condition was determined when the inflow rate of water wasequal to the outflow rate. At this point, the soil column was considered to be asaturated soil and the final infiltration rate was measured.

    Table 1. Physical properties of the soil used in this study.

    Soiltexture Sand (%) Silt (%) Clay (%)

    Bulkdensity

    (Mg m73)

    Initial watercontent

    (cm3 cm73)

    Saturatedwater content(cm3 cm73)

    Loamy sand 71 19 10 1.55 0.012 0.37

    Table 2. X-ray diffraction analysis of the bentonite used in this study (Ibrahim-Saeedi andSepaskhah 2011).

    Parameter Quantity (%)

    Montmorillonite, (Na, Ca)0.3(Al, Mg)2Si4O10(OH)2,nH2O 55.00Gypsum, CaSO4 5.00Muscovite, KAl2Si3AlO10(OH)2 4.00SiO2 24.00CaCO3 7.00NaCl 3.00Fe2O3 2.00

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  • Measured cumulative infiltration was fitted to the Kostiakov equation as follows:

    Z ktm 1

    where Z is the cumulative infiltration (CI) in cm, t is the elapsed time in min and kand m are constants. Furthermore, the LewisKostiakov equation was fitted to themeasured CI as follows:

    Table 3. Chemical analysis of the fresh water used in this study.

    Parameter Unit Quantity

    Electrical conductivity dS m71 0.710pH 7.160Cl7 mmolc L

    71 0.056HCO3

    7 mmolc L71 5.200

    Na mmolc L71 0.690

    Ca2 mmolc L71 3.000

    Mg2 mmolc L71 4.120

    K mmolc L71 0.049

    Figure 1. Experimental set-up for infiltration measurement.

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  • Z k0tm0 ift 2

    where if is the final infiltration rate and k0 and m0 are constants.

    Results and discussion

    CI as a function of elapsed time at different bentonite application concentrations isshown in Figure 2. Fitted constants of Equation (1) are shown in Table 4. Values ofmare not influenced by bentonite concentration and its mean value is 0.485. The valueof k was reduced by 36% at a bentonite concentration of 2 g L71, by 27% at 4 g L71

    with respect to 2 g L71 and by 29% at 6 g L71 with respect to 4 g L71 (Table 4).As shown in Figure 2, CI decreased with increasing bentonite solution

    concentration. The relationship between k and the bentonite concentration (Figure 3)is as follows:

    k 2:839 exp 0:183b 3

    R2 0:99; n 4; SE 0:0461; p < 0:003 4

    Table 4. Mean values of the Kostiakov infiltration coefficient (k), LewisKostiakovinfiltration coefficient (k0) and final infiltration rate (if) at different bentonite concentrations.

    Bentonite concentration (g L71) k (cm min7m) k0 (cm min7m0) if (cm min

    71)

    0 2.940a* 2.894a 0.207a2 1.869b 1.909b 0.085b4 1.364c 1.416c 0.048c6 0.964d 1.048c 0.032d

    Note: Means followed by the same letter are not significantly different at the 5% level of probability usingDuncans multiple range test.

    Figure 2. Cumulative infiltration as a function of elapsed time at different bentoniteconcentrations.

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  • where k is the constant of Kostiakov equation in cm min7m and b is theconcentration of bentonite in irrigation water in g L71. Equation (3) can be usedto estimate the value of k for bentonite concentrations other than those used in thisexperiment.

    Addition of bentonite to the soil led to a decrease in the infiltration rate due tothe blockage of soil pores by bentonite particles. With further application of abentonite solution to the soil column, a thin layer of bentonite is formed on the soilsurface, similar to a crust, and reduces if. Values of if are given in Table 4. The valueof if decreased by *59% with a bentonite solution of 2 g L

    71 and by *43.5 and33.5% on increasing...

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