Impact of water quality on crust strength of a gel-conditioned calcareous sandy soil

SOIL TECHNOLOGY

vol. 3, p. 57-62

Cremlingen 1990

I M P A C T OF WATER QUALITY O N C R U S T S T R E N G T H OF A G E L - C O N D I T I O N E D C A L C A R E O U S S A N D Y SOIL A.M. AI-Omran, A.A. Shalaby, M.A. Mustafa & A.M. AI-Darby

Riyadh Summary

tention and in limiting deep percolation losses of sandy soils (MILLER 1979, The effects of EC and SAR of twelve HEMYARI & NOFZIGER 1981, ALsynthetic waters on modulus of rupture OMRAN et al. 1987, MUSTAFA et of a calcareous sand (typic Psamments) al. 1988). However, they may actreated with three gel-conditioners (0.4% centuate or reduce crust strength deJalma, 0.4% StaWet and 0.4% Hydrogel) pending upon conditioner type and its were investigated. rate of application (WILLIAMS et al. Under salt-free conditions, the addi1966, PAGE & QUICK 1979, HEtion of gel-conditioners substantially inMYARI & NOFZIGER 1981, ALcreased the crust strength of sand bri- OMRAN et al. 1988). It is well esquets. Under salty conditions, addition tablished that crusting imposes serious of Jalma or StaWet markedly increased soil physical limitations to plant growth MOR of sand, whereas addition of Hy- (e.g. RICHARDS 1953, ARNDT 1965, drogel slightly decreased or increased BARLEY 1976). At 0.4%, super slurper MOR depending on EC amd SAR of (hydrolysed starch polyacrylonitrile graft water used. co-polymer) reduced crust strength of The results showed that M O R of the sandy loam, loamy sand and clay loam simulated crusts of sand increased with soils (HEMYARI & NOFZIGER 1981). increase in SAR and decrease in EC. It At low rates (<0.4%), Jalma, a super was concluded that at relatively low salt gel containing 24.5% humic acids and concentration (<1 dSm-i), the addition 3,8% polysaccharides, reduced moduof 0.4% Jalma or 0.4% StaWet may cre- lus of rupture (MOR) of sandy loam, ate some crusting problems. sandy clay loam and clay loam soils but had no effect on MOR of a loamy sand. Whereas at high rates (>0.4%) it 1 Introduction markedly increased MOR of all the soils Some synthetic gel-conditioners proved studied (AL-OMRAN et al. 1988). In arid regions it is important to to be effective in increasing water reconsider the interactive effects of gelISSN 0933-3630 conditioners and water quality on crust @1990 by CATENAVERLAG, strength of sandy soils. This is, parD-3302 Cremlingen-Destedt,W. Germany ticularly, true in Saudi Arabia where 0933-3630/90/5011851/US$ 2.00 + 0.25 SOIL TECHNOLOGY--A cooperating Journal of CATENA

Al-Omran, Shalaby, Mustafa & A1-Darby

58

Product Name ManufactureN a m e

ChemicalProperties

Rate Used

Sta Wet

Polysorb, Inc. P.O. Box 99, Srnelterville ID, 83868, U.S.A.

Starch-grapht-poly, (acrylamide-Co-Naacrylate)

0.4%

Jalma

S.A.I.D. Rue du Stude 69120 Vaulx en Velin France

24.5% humie acid 3.8% polysaccharides 1.9% Fulvic acids

0.4%

Hydrogel

Finn-Corporation P.O. Box 8068 2525 Duck Creek R. Cincinnati, Ohio 45208 U.S.A.

(Starch-poly-Co. K acrylate)

0.4%

Tab. 1: Properties of the soil conditioners. saline ground and treated sewage waters are used for irrigating sandy soils. The present paper reports the joint effects of electrical conductivity and sodium adsorption ratio of synthetic waters and three gel-conditioners on the modulus of rupture of a sandy soil.

2

Materials and methods

A bulk surface (0-25 cm) calcareous sample from a sand soil (Typic Torripsamments) was collected from the college experimental farm at Deirab, Saudi Arabia. The sample was air-dried and passed through 2-mm sieve. Particle-size analysis was carried out by the international pipette method. Soil organic matter was determined by the Walkley and Black method and calcium carbonate equivalent by acid neutralization ( C H A P M A N & P R A T T 1961). Soil pH was measured electrometrically in a saturated soil paste and the conductivity of the saturation extract (ECe) was measured by a conductivity bridge ( R I C H A R D S 1954). Sand, silt and clay were 90, 4 and 6%,

respectively. The percentage o f organic matter, pH, ECe and CaCO3 percent were 0.04, 7.8, 0.65 dSm -1 and 25.3%, respectively. The synthetic conditioners used were Jalma, StaWet and Hydrogel (tab.l). The waters used included distilled water (simulating rain water) and 12 mixed CaC12-NaC1 salt solutions differing in EC (1, 2, 4, 8) and SAR (5, 10, 20) (simulating irrigation ground waters). Three soil subsamples were separately hand-mixed with predetermined quantities of the three conditioners in form of gel to yield a concentration of 0.4% (on dry basis, which is the rate recommended by some research workers ( M I L L R A 1979, A L - O M R A N et al. 1987)). The treated subsamples were then air-dried and crusted to pass through 2 mm-sieve. Thus, the treatments consisted of three conditioners: 0.4% Jalma, 0.4% StaWet, 0.4% Hydrogel and control (unconditioned soil), and 13 waters. Modulus of rupture of simulated crusts (briquets) was measured using the apparatus and closely following the procedure of R I C H A R D S (1953), with exSOIL T E C H N O L O G Y - - A cooperating Journal of CATENA

Gel-Conditioned Sandy Soil

ception of 24 hours saturation in water or salt solutions. The details of the procedure are given in R I C H A R D S (1954). Six replicate measurements were made for each treatment. For analysis of variance complete randomization was assumed.

3 3.1

Results and discussion Conditionereffect

Under salt-free conditions (distilled water), the addition of gel-conditioners (0.4%) substantially increased the crust strength of the sand briquets. The modulus of rupture (MOR) of Jalma-, StaWet, and Hydrogel-treated sandy soils were about 11, 7 and 3 times that of the untreated sandy soils. The highest M O R caused by Jalma may be attributed to cementation action of humic acid and polysaccharides. StaWet being a copolymer Na-acrylate was more effective in cementation than Hydrogel which is a copolymer K-acrylate. Our previous research showed that the addition of 0.4% Jalma reduced M O R of sandy loam, sandy clay loam and clay loam soils but had no effect on M O R of a loamy sand. It was argued that at this rate Jalma promoted soil aggregation and that cross-linking between the microaggregates were incomplete. It was thus explained that the improved aggregation was responsible of lowering M O R of the three medium to fine-textured soils. In the case of loamy sand its already minimal M O R value (= 0 kPa) was not influenced by the aggregation effect of the conditioners (ALO M R A N et al. 1987, A L - O M R A N et al. 1988). In the present study it seems that 0.4% Jalma was sufficient to cause complete cross-linking between the corn-

SOIL TECHNOLOOY--A cooperating Journal of CATENA

59

pacted sand particles a n d thus cementing them by the drying process that followed the water saturation process. This explains the increase in M O R of sand due to the addition o f 0.4% Jalma. Under salty conditions (salt solutions), addition of Jalma or S t a W e t markedly increased M O R o f sandy soils, whereas the addition of H y d r o g e l slightly decreased or increased M O R depending upon EC and SAR o f the water used (figs. 1 & 2). At SAR = 5 and EC = 1 dSm -1, M O R o f the Hydrogel-treated sandy soil was similar to t h a t of the control, but at E C > 2 dSm -1 it was lower than the control. At S A R = 20 and EC < 6 dSm - t M O R o f the Hydrogeltreated sandy soil was higher than that of the control whereas at E C > 6 dSm -1 it was lower than it.

3.2

Salinity effect

Fig.1 shows the effect o f E C upon M O R at three SAR values. Because sand particles are inert, M O R values of the unconditional sand briquets were not significantly affected by EC. The addition of gel-conditioners m a d e M O R of the simulated crust susceptible to salinity effect. The effect was d e p e n d e n t upon the type of the conditioner a n d SAR, much more so on the former t h a n the latter. In general, at a given S A R , M O R of gel-conditioned briquets decreased with increase in EC. The decrease was slight in the case of Hydrogel, moderate o f StaWet and marked for Jalma. At S A R = 5 the average rate of decrease in M O R with increase in EC (kPa/dSm -1) were 5.9, 1.7 and .8 for Jalma, StaWet and H y d r o gel, respectively. At S A R = 20, these rates for the same conditioners in sequence were 5.7, 2.5 and 1.4. At SAR = 5

Al-Omran, Shalaby, Mustafa & A1-Darby

60

?0

and 65%. A t the low salt concentrations (EC < 1 dSm -1) crust strength was in the following decreasing order: J a l m a - > StaWet-> Hydrogel-treated sandy soils. Whereas at the highest salt concentration the order was as follows: S t a W e t - > J a l m a - > Hydrogel-treated sandy soils.

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Fig. i: Modulus of rupture of unconditioned (-o-) or conditioned sand (-.Hydrogel, -A- StaWet, -+- Jalma) as affected by electrical conductivity ( EC ) at specified sodium adsorption ratio (SAR) of water. M O R o f Jalma-, StaWet- and Hydrogeltreated sand briquets were reduced 79, 31 and 62%, respectively due to increase in EC from 1 to 8 dSm -1. At SAR = 20 these reductions for the same conditioner treatments in sequence due to the same increase in EC were about 67, 36

3.3

Sodicity effect

Fig.2 depicts the effect of SAR and M O R at four EC values. It is evident that M O R values of the control briquets were not affected by SAR, whereas that of the gel-conditioned briquets increased with increase in SAR. The SAR effect was more pronounced at EC = 2 d S m -1 and subdued at EC = 8 d S m -1. At EC = 2 d S m -~ thc average rate of increase in M O R with increase in SAR f r o m 5 to 20 was 4.5, 2.8 and 1.3 for Jalma-, StaWetand Hydrogel-treated briquets, respectively. These rates at EC = 8 d S m -1 due to the same increases in SAR a n d for the same conditioner treatments in sequence were 1.2, 0.5 and 0.2. T h e results show that M O R of the simulated crust o f a sandy soft increased with increase in SAR and decrease in EC. Both factors promote swelling of the gel-conditioners ( J O H N S O N 1984). Swelling m a y cause a larger proportion of the polymer segments per molecule to extend from the a d s o r b e n t surface. This polymer extention m a y p r o m o t e the complete cross-linking betwcen the compacted sand particles during the saturation stage and causes more complete cementation on the subsequent drying stage. High EC and low S A R values cause shrinkage o f the gel, closer packing on the adsorbent surface, incomplete cross-linking and consequent incomplete cementation. Decrease in E C and in-

SOIL TECHNOLOGY--A cooperating .~ournal of CATENA

Gel-Conditioned Sandy Soil

61

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Fig. 2: Modulus of,' rupture of unconditioned (-o-) or conditioned sand (-.- Hydrogel,

-A- StaWet, -4-- Jalma) as affected by sodium adsorption ratio (SAR) at specified electrical conductivity (EC) of water. crease in SAR may also enhance dispersion of the colloidal material and consequently cause closer packing of the soil particles upon drying and hence increase crust strength (e.g. R I C H A R D S 1953, PAINULI & A B R O L 1986). However, in the present study this dispersion effect may be insignificant in view of the minute amount of clay in the soil studied. A L Y M O R E & SILLS (1982) selected a M O R value of 60 kPa as a lower limit for soils with crusting problems. Thus, at relatively low salt concentrations (<1 dSm -t) the addition of Jalma and StaWet may create some crusting problems. This may be true if patches o f high concentrations

SOIL TECHNOLOGY--A cooperating Journal of CATENA

are formed due to uneven distribution of the gel-conditioners. In Saudi Arabia most irrigation waters are o f higher salinity level specially during summer and thus the use of thee conditioners may not cause crust problems, but may limit their water holding capacity. In spite of its obvious importance, the economic aspect was not an objective of this study. However, present cost-benefit analysis may limit field application o f some gel-conditioners at the rates suggested by studies such as the present one. References AL-OMRAN, A.M., MUSTAFA, M.A. & SHALABY, A.A. (1987): Intermittent evaporation

Al-Omran, Shalaby, Mustat'a ~ A1-Darby

62

from soil columns as affected by a gel-forming conditioner. Soil Sci. Soe. Am. J. 51, 1593-1599. AL-OMRAN, A.M., MUSTAFA, M.A. & MURSI, M. (1988): The influence of a gel conditioner on water retention and crust strength of some calcareous soils. J. Coll. Agric. King Saud Univ. 10, 199-207.

WILLIAMS, B.G., GREENLAND, D.J. & QURIK, J.P. (1966): The adsorption of polyvinylalcohol by natural soil aggregates. Aust. J. Soil Res. 4, 131-143.

ALYMORE, L.A.G. & SILLS, I.D. (1982): Characterization of soil structure and stability using modulus of rupture-exchangeable sodium percentage relationship. Aust. J. Soil Res. 20, 213-224. ARNDT, W. (1965): The impedance of soil seals and the forces of emerging seedlings. Aus. J. Soil Res. 3, 55-68. BARLEY, K.P. (1976): Mechanical resistance of the soil in relation to the growth of roots and emerging shoots. Agrochimica 20, 173-182. CHAPMAN, H.D. & PRATT, P.F. (1961): Methods of analysis for soils, plants and waters. University of California, Division of Agriculture Sciences, 309 p. HEMYARI, P. & NOFZIGER, D.L. (1981): Super slurper effects on crust strength, water retention and water infiltration of soils. Soil Sci. Soc. Am. J. 45, 799-801. JOHNSON, M.S. (1984): Effect of soluble salts on water absorption by gel-forming soil conditioners. J. Sci. Food Agric. 35, 1063-1066. MILLER, D.E. (1979): Effect of H-SPAN on water retained by soils after irrigation. Soil Sci. Soc. Am. J. 43, 628-629. MUSTAFA, M.A., AL-OMRAN, A.M., SHALABY, A.A. & AL-DARBY, A.M. (1988): Horizontal infiltration of water in soil columns as affected by a gel-forming conditioner. Soil Sci. 145, 330--336. PAGE, E.R. & QUICK, M.J. (1979): A comparison o f the effectiveness of organic polymers as soil anticrusting agents. J. Sci. Food Agric. 30, 112-118. PAINULI, D.K. & ABROL, I.P. (1986): Effects of exchangeable sodium on crusting behaviour of a sandy loam soil. Aus. J. Soil Res. 24, 367-376. R/CHARDS, L.A. (1953): Modulus of rupture as an index of crusting of soil. Soil Sci. Soc. Am. Proc. 17, 321-323. RICHARDS, L.A. (1954): Diagnosis and improvement of saline and alkali soils. U.S. Dep. Agric. Handbook No. 60.

Addresses of authors: A.M. Al-Omran Associate Professor of Soil Science A.A. Shalaby Research Assistant M.A. Mustafa Professor of Soil Science A.M. AI-Darby Assistant Professor of Soil Science Soil Science Department College of Agriculture, KSU Riyadh, Saudi Arabia

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