effect of mixed cation solutions on hydraulic soil properties

Agriculture Water Management, 6 (1983) 15--25 15 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

EFFECT OF MIXED CATION SOLUTIONS ON HYDRAULIC SOIL PROPERTIES

R.S. SIYAG, R. PAL, S.R. POONIA and T.C. BARUAH

Department of Soils, Haryana Agricultural University, Hissar-125004 (India)

(Accepted 9 September 1982)

ABSTRACT

Siyag, R.S., Pal, R., Poonia, S.R. and Baruah, T.C., 1983. Effect of mixed cation solutions on hydraulic soil properties. Agric. Water Manage., 6: 15--25.

Hydraulic conductivity (K) and soil water diffusivity (D) characterizing water flow under saturated and unsaturated conditions, respectively, were determined for a sandy loam and a clay loam soil, using water with different combinations of total electrolyte concentrations, C (i.e., 20, 40, 80, 125 and 250 meq 1-') and sodium adsorption ratios, SAR (i.e., 0, 20, 30, 40, 80 and ~ mmole 1-v~). Both K and D were found to increase with C and decrease with SAR. In low sodium adsorption ratio ranges (i.e., up to 20) the requirement of electrolyte concentration to maintain relative hydraulic conductivity = 0.5 was relatively more for sandy loam than for clay loam soil. However, the trend for electrolyte concentration requirements for the two soils was reversed at high sodium adsorption ratios (i.e. > 20). A spline function was used to draw the best fitting line through the data points of horizontal absorption experiments.

INTRODUCTION

Considerable efforts have been made to study the effect of total salt concentration and cation composition on the saturated hydraulic conductivity of soils (Quirk and Schofield, 1955; McNeal and Coleman, 1966; McNeal, 1968; Rowell et al., 1969; Pandey et al., 1974; Pal et al., 1980). Unsaturated water transmission parameters such as soil water diffusivity and capillary conductivity have also been studied extensively (Gardner et al., 1959; Saha, 1976; Russo and Bresler, 1977; Pal et al., 1980). However, information on these parameters for different soil types from arid and semi-arid regions is meagre. This paper reports the quantitative effect of different salt solutions on the saturated and unsaturated hydraulic properties of two different soil types from a semi-arid region where water used for irrigation is generally brackish.

MATERIALS AND METHODS

Surface (0--15 cm) samples of a sandy loam and a clay loam soil were collected from the Experimental Farm of Haryana Agricultural University,

0378-3774/83/$03.00 © 1983 Elsevier Science Publishers B.V.

16

TABLE I

Properties of the soils

Characteristics Hansi Hissar soil soil

pH 8.6 8.2 Electrical conductivity, ECL:2 (mS) 0.9 0.3 Cation exchange capacity, CEC (meq/100 g) 14.6 9.3 CaCO3 (%) 0.8 0.3 Sand (%) 42.0 65.0 Silt (%) 22.0 16.0 Clay (%) 36.0 19.0 Texture Clay Sandy

loam loam

Hissar and the Government Agricultural Farm, Hansi, respectively. They were air-dried and passed through a 2 mm sieve. Some of their physico-chemical properties are given in Table I.

Saturated hydraulic conductivity was determined using brass permeameters (10--12 cm long and 8 cm internal diameter). The permeameters were uniformly packed to a bulk density of 1.5 + 0.03 g cm -3 for the sandy loam soil and 1.4 -+ 0.03 g cm -3 for the clay loam soil. After placing them vertically, solutions with different SAR and total electrolyte concentration C were applied at the top. All the solutions (i.e. C, 250, 125, 80, 40 and 20 meq 1-1 and SAR, 0, 20, 30, 40, 80 and oo mmolel~ 1-1/2 ) were prepared using chloride salts of Na ÷, Ca 2÷ and Mg 2÷. Ca 2÷ and Mg 2÷ were kept in 1:1 ratio on an equivalent basis. A constant hydraulic head was maintained using a Mariotte system. Through each soil column solutions of differing C but the same SAR were passed until a steady state both with respect to the composition of the effluent and the flow rate was attained. Experiments were carried out in a se- quence of decreasing electrolyte concentrations.

Soil water diffusivity values were determined using horizontal absorption data (Bruce and Klute, 1956). Plexiglass columns of 30 cm length and 4.05 cm internal diameter were constructed by joining 0.9 and 1.5 cm thick plexiglass pieces as shown in Fig. 1. For horizontal absorption experiments the bulk soil samples were equilibrated separately with water of different SAR. The soil samples were leached with a series of solutions with gradually electrolyte concentrations but the same SAR, until the electrolyte concentration of the effluent attained a value of less than 0.01 N. The excess salts were re- moved by washing the soil with 90% ethanol and petroleum ether in succes- sion. The equilibrated soil samples were air-dried and passed through 2-mm sieve. The columns were filled as uniformly as possible with air-dried soil to the bulk densities mentioned above. The columns were placed horizontally and water of the same ionic composition with which the soil samples had already been equilibrated was introduced at the inlet and from a Mariotte burette at a

BURETT!

1*-5-'1

I I

J i

', i I t

R . . ~ 12.5 N LEFT SIDE ELEVATION

E Cr~ U ~rJ ,O (P. "

1~ 30 cm >1 FRONT ELEVATION

r C m

EGULATOR

I~ 12.5

RIGHT SIDE ELEVATION

17

SINTERED GLASS DISCT[' ~

PLAN ELEVATION

Fig. 1. Experimental unit for horizontal infiltration.

constant suction of about 2 cm of water. The experiment was continued until the wetting front had run a distance of 25 cm. The time of infiltration was noted and the water source disconnected. The segments were quickly separated to avoid any further movement of the water. Soil samples were collected from the segments for gravimetric moisture determination. The weighted mean diffusivity, D, was calculated using the method of Gardner et al. (1959}.

The spline function (Erh, 1972) was applied to the horizontal absorption data to draw a continuous and smooth curve through data points.

RESULTS AND DISCUSSION

The values of saturated hydraulic conductivity in relation to total electrolyte concentration and SAR are presented in Table II. The results reveal that there was a gradual decrease in the value of K with a decrease in C and an increase in SAR. The behaviour of the clay loam soil was almost the same as that of the sandy loam soil except that the absolute values of K were far smaller. These results show that though K increased with C at all SARs in both soils, the effect of C was more pronounced at higher SAR values.

The relative saturated hydraulic conductivities K* (= K SARi Ci/K SAR0 C2s0) for sandy loam and clay loam soils in relation to SAR at different electrolyte concentrations are shown in Figs. 2 and 3, respectively. In both softs at C20, the decrease in K* was sharp when SAR increased from 0 to 20 and became gradual with further increases in SAR. With an increase in C, the sharp decrease in K* shifted towards the higher SAR values. At SAR0, the

18

T A B L E II

Ef fec t o f e l ec t ro ly te c o n c e n t r a t i o n (C) and sod ium a d s o r p t i o n ra t io (SAR) on s a tu r a t ed hydrau l i c conduc t iv i t y , K (cm h -1)

C SAR ( m m o l e 1/2 l "/2) (meq l -~ )

0 20 30 40 80 ~¢

Sandy loam soil 20 0 .29 0 .10 0.07 0.04 0 .014 0 .007 40 0 .37 0 .28 0 .16 0.10 0 .028 0 .018 80 0.38 0 .36 0.28 0.22 0.12 0 .040

125 0 .54 0 .48 0.42 0.35 0.28 0.11 250 0.68 0 .64 0 .54 0.48 0.38 0.18

Clay loam soil 20 0.14 0 .069 0 .038 0 .028 0 .0082 0 .004 40 0 .24 0.15 0 .10 0 .058 0 .028 0 .013 80 0 .29 0.24 0.15 0.11 0.08 0 .031

125 0.31 0.28 0.17 0.15 0.12 0 .050 250 0 .37 0.32 0 .26 0.24 0 .20 0 .125

.¢

¢J

<=

,l-

tn

>=

n,

10-1

lo-Z 0

C ( meq 1-1 )

o 20 • 4 0 • 8 0 n 125 • 2 5 0

! 2 0

SODIUM

i I i // 4O 6 0 8 0

ADSORPTION RATIO, S A R ( m m o l e 1/2 [ -1/2- )

cC

Fig. 2. E f fec t of SA R and e lec t ro ly te c o n c e n t r a t i o n on relat ive sa tu ra t ed hydrau l i c conduc t iv i ty o f s andy loam soil.

19

10 0

z O u u .J

~: lo -1

J

-2 10

I i ! i i

ZO 4 0 6 0 8 0 =C

S O D I U M A D S O R P T I O N RATIO,SAR (rnmole 1/2 [ - 1 / 2 )

Fig. 3. Effect of SAR and electrolyte concentration on relative saturated hydraulic conductivity of clay loam soil.

effect of an increase in C on K* was less than that at higher SARs. The per- meabili ty studies of Quirk and Schofield (1955) on a silty loam soil showed that an electrolyte concentrat ion of 10 meq 1-1 might give a stable permeability up to an exchangeable sodium percentage (ESP) of about 20. However, the results of the present investigation show that electrolyte levels of 250 meq 1-1 at SAR2o and higher do not give the same value of K* as that for C2s0SAR0. This may be attr ibuted to the higher degree of dispersion (break-down of tactoids into smaller size or individual soil particles) in these soils. McNeal et al. (1968) also could not achieve a stable hydraulic conductivity in the case of sandy loam soil at 50 meq 1-1 total electrolyte concentration, when SAR was 20 or higher.

Tbe reduction in K of these soils in relation to SAR is at tr ibuted to swelling, dispersion and migration of clay particles which result in the reorientation of soil particles and consequently affect the pore size distribution. Both swelling and movement of clay particles cause blocking of water conducting pores and hence a decrease in K. McNeal et al. (1966) in their studies found swelling to be more important than dispersion and migration of clay particles in affecting K. However, Shainberg and Caiserman (1971) reported migration of clay particles to be more important at low SAR/ESP (i.e., < 15) in reducing K. They explained it on the basis of the demixing of Na ÷ and Ca 2÷ (i.e., prefer- ence of Na ÷ for external exchange sites and that of Ca 2÷ for internal exchange sites), which occurs at low SAR/ESP. The effect of this phenomenon was more pronounced on the dispersion and migration of clay particles than on swelling.

20

Contrary to this, Rowell et al. (1969), envisaged swelling as the governing factor for K until the dispersion and migration of particles in response to SAR began. Chen and Benin {1975), on scanning microscopic observations, concluded that the local orientation of the clay particles rather than migration might be responsible for reducing K. The favourable effect of C might be caused by reduced swelling and dispersion of clay particles. It is clear from this discussion that, based on the experimental technique adopted, the stress on the relative importance of different parameters in affecting K varies a great deal. It may, however, be pointed out that the relative contr ibution of swelling and dispersion at a given C is difficult to evaluate because both swelling and dispersion take place simultaneously with an increase in SAR/ESP.

The combinations of electrolyte concentration and SAR, which yielded K* = 0.5 are shown in Table III. The salt concentration associated with a 50% reduction in hydraulic conductivity increased as the SAR of the solution increased. To maintain a value of K* = 0.5, the total electrolyte concentration requirements were higher for the sandy loam soft than for the clay loam soil when the SAR of the percolating water was relatively low (i.e., SAR up to 20). However, the reverse was true when the SAR of the percolating water was relatively high (i.e., SAR30 or higher). This suggests that apart from the composi t ion of irrigation water in terms of its total soluble salt concentration and SAR, the texture of the soil is equally important in assessing changes in water conducting properties of soil for water of different compositions.

The values of D(0 ) corresponding to different electrolyte concentrations and sodium adsorption ratios at different moisture contents are given in Figs. 4 and 5 for the sandy loam and clay loam soil respectively. In general, D(O ) increased with an increase in C and 0 and a decrease in SAR.

The values of D, as affected by the total electrolyte concentration and SAR of the solution, are given in Table IV for both soils. In general, higher D values were obtained in the sandy loam soil than in the clay loam soil. At a given electrolyte concentration, D decreased with an increase in SAR. In clay loam soil the decrease was sharper at the first increment of SAR (i.e., from 0 to 20)

TABLE III

Combinations of electrolyte concentration (C) and sodium adsorption ratio (SAR) at which relative hydraulic conductivity decreased to 50%

SAR Electrolyte concentration, C (meq 1-') (mmole'/2 l- ~/2)

Sandy loam Clay loam

0 32.0 28.0 20 66.0 62.0 30 94.0 120.0 40 128.0 170.0 80 182.0 222.0

21

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22

TABLE IV

Effect of e lectrolyte concentration (C) and sodium adsorption ratio (SAR) on weighted mean diffusivity (D)

C SAR (mmole V~ 1 -V2 ) (meq l -i )

0 20 30 40 80

Sandy loam soil 20 54.50 52.00 4.60 0.80 0.10 - - 40 56.00 53.00 12.10 10.00 4.00 0.06 80 58.00 54.00 18.90 16.00 10.60 0.40

125 62.00 55.00 23.40 21.00 14.90 1.40 250 71.20 60.20 28.50 24.50 22.90 5.50

Clay loam soil 20 31.77 5.46 2.74 1.29 0.11 - - 40 35.86 9.90 7.05 5.04 1.82 0.05 80 36.70 10.20 8.90 6.85 2.86 0.45

125 37.00 11.90 9.10 7.60 4.76 1.26 250 38.74 14.78 13.71 12.71 6.28 5.90

10 0 ~

:>

b.

Q

Z < bJ ~E

O bJ

w

w

lO-1

10 -2

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\ \ \,,

% \

%%

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o 20 ~ • 40

4 80 o 125 \ • 250 \

\ \

; ' 0 40 60 80 oC

1/2 i - 1 / 2 ) SODIUM AOSORPTION RATIO, SAR ~rnmole

Fig. 6. Effect o f SAR and electrolyte concentration on relative weighted mean diffuvisity o f sandy loam soil.

23

and then became more gradual at higher SAR's. On the other hand, in sandy loam soil a sharp decrease of D occurred at the increment of SAR from 20 to 30. The decrease of D in both soils was more pronounced at lower electrolyte levels. The effect of electrolyte concentration on D in sandy loam was small up to SAR 20. However, in clay loam soil the effect of electrolyte concentration was small only at SAR0. At high SARs, the effect of C became more pronounced in both soils.

Gardner et al. (1959), found that the effect of the electrolyte concentration on D at different ESP values of soils was small at ESP0, while at ESPy00 it was more than a thousand fold. In the present study, at SARs0, the increase in D was about 200 times in the sandy loam soil and about 60 times in the clay loam soil when C increased from 20 to 250 meq 1-1.

The values of relative weighted mean diffusivity (D* = D SARi Ci/D SARo C2s0), corresponding to different salt concentrations and SARs are shown in Figs. 6 and 7. There was a sharp decrease in the value of D* at SAR30 in the

1 0 0 . , ,

,g c~

:> Ln

o

z

w

o h i

0

t~

W

_1 W

10-1

lo'z

I lo-3

SODIUM

C ( meq 1-1 ) ~

o 20 • 40

a 125 ~ • 250

20 4.0 60 80

ADSORPI" ION R A T I O , S A R ( 'mmole I/2 [ -1/2 )

Fig. 7. E f f e c t o f S A R and e l ec t ro ly t e concentra t ion on relative we ighted mean di f fuvis i ty o f c lay loam soil .

24

sandy loam soil and at SAR20 in the clay loam soil. At higher SARs, there was a relatively gradual decrease in D ~. At a given SAR, O ~ increased with an increase in C; the effect of C being more pronounced at high SARs in both soils. In the sandy loam soil, up to SAR:0, the increase in D* was small when C increased from 20 to 250 meq 1-1. In the clay loam soil, however, this mar- ginal increase in D* with an increase in C was observed at SAR0 only.

The slope of the curves giving the relation between the moisture content and the Boltzmann function ~ = x ~ / t is needed to calculate D(O ) by the method

of Bruce and Klute (1956 }. For this purpose, we need smooth curves through data points. The use of a spline function is helpful in this respect. The k--0 relationship, as obtained by applying the spline function method for the sandy loam and the clay loam soils, is given in Fig. 8.

In conclusion it may be stated that a certain percentage reduction in saturated hydraulic conductivity at a given SAR corresponds to different electrolyte concentrations for the two soils studied. Further, such concentrations were

0.55

0 5 0

0.,',5

0.50

0.35 E u

u 0.30

0.25

© L) Ld 0.20 Oc

5 o.15 E

CLAY LOAM . ~

a EXPERIMENTAL / • " SPLINE FUNCTION /

SANDY LOAM _ /

o EX PERIMENTAL I SPLINE FUNCTION

0.10

0 .05

i i I i

O 1.O 2.0 3.0 8.O BOLTZNANN

to 4.t0 5.0 6.0 7.0 FUNCTION, X (cm h " l /z)

Fig. 8. ~,---o relationship of sandy loam soil at C:oSAR30 and clay loam soil at C2s0SAR2o.

25

higher/lower in light textured than in heavy texture soils at lower/higher SAR Hydraulic properties of soils can be explained by phenomena like swelling,

dispersion and migration of clay particles, but it is difficult to quantitatively evaluate their relative contribution.

REFERENCES

Bruce, R.R. and Klute, A., 1956. The measurement of soil moisture diffusivity. Soil Sci. Soc. Am. Proc., 20: 458--462.

Chen, Y. and Banin, A., 1975. Scanning electron microscope observations of soil structure changes induced by sodium-calcium exchange in relation to hydraulic conductivity. Soil Sci., 120: 428--436.

Erh, K.T., 1972. Application of the spline function to soil science. Soil Sci., 114: 333--- 338.

Gardner, W.R., Mayhugh, M.S., Goertzen, J.O. and Bower, C.A., 1959. Effect of electrolyte concentration and exchangeable sodium percentage on diffusivity of water in soils. Soil Sci., 88: 270--274.

McNeal, B.L., 1968. Prediction of the effects of mixed salt solutions on soil hydraulic conductivity. Soil Sci. Soc. Am. Proc., 32: 190--193.

McNeal, B.L. and Coleman, N.T., 1966. Effect of solution composition on soil hydraulic conductivity. Soil Sci. Soc. Am. Proc., 30: 308--312.

McNeal, B.L., Norwell, W.A. and Coleman, N.T., 1966. Effect of solution composition on swelling of extracted soil clays. Soil Sci. Soc. Am. Proc., 30: 313--317.

McNeal, B.L., Layfield, D.A., Norvell, W.A. and Rhoades, J.D., 1968. Factors influencing hydraulic conductivity of soils in the presence of mixed salt solutions. Soil Sci. Soc. Am. Proc., 32: 187--190.

Pal, R., Singh, S. and Poonia, S.R., 1980. Effect of water quality on the water transmission parameters of unsaturated soils. J. Indian Soc. Soil Sci., 28: 1--9.

Pandey, R.N., Narain, B. and Pathak, A.N., 1974. Effect of electrolyte concentration on the hydraulic conductivity of Bundelkhand soils. J. Indian Soc. Soil Sci., 22: 191--192.

Quirk, J.P. and Schofleld, R.K., 1955. The effect of electrolyte concentration on soil permeability. J. Soil Sci., 6: 163--178.

Rowell, D.L., Payne, D. and Ahmad, N., 1969. The effect of the concentration and movement of solutions on swelling, dispersion and movement of clay in saline and alkali soils. J. Soil Sci., 20: 176--188.

Russo, D. and Bresler, E., 1977. Effect of mixed Na--Ca solutions on the hydraulic properties of unsaturated soils. Soil Sci. Soc. Am. J., 41: 713--717.

Saha, A.K., 1976. Soil moisture transmission characteristics as influenced by exchangeable sodium percentage and electrolyte concentration. Ph.D. Thesis, HAU, Hissar, 87 pp.

Shainberg, I. and Caiserman, A., 1971. Studies of Na/Ca montmorillonite systems. 2. The hydraulic conductivity. Soil Sci., 111: 276--281.

effect of mixed cation solutions on hydraulic soil properties

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