PenanikaJ. Tcop. Agric. Sc;. 18(2),83-88(1995) ISSN,012lHi128© Universiti Pertanian Malaysia Press

Modification of Soil Structure of Sand Tailings: I. Preliminary Study on theEffect of Organic Amendment and Iron on Soil Aggregation

A. M. MOKHTARUDDIN and M. NORHAYATIDepartment of Soil Science, Faculty of Agriculture,

Universiti Pertanian Malaysia, 43400 UPM Serdang,Selangor, Malaysia

Keywords: structure, sand tailings, amendment, aggregation

ABSTRAK

Keberkesanan efluen kiln.ng keln.pa sawit kering yang mengandungi 14 % karbon organik dan In.rutan besi daln.mmenggaln.kkan pengaggregatan di tanah pasir bekas lombong dikaji. Penambahan besi atau efluen ki/ang keln.pasawit kering pada kadar 20 dan 60 t hal tidak memberikan kesan bermi ke atas pengaggregatan dan kestabilantanah pasir. Pada kadar 100 thai, efluen kiln.ng keln.pa sawit memberikan kesan bermi ke atas kestabiln.naggregat. Dengan penambahan 0.1 % Fe, kadar eflum kilang keln.pa sawit kering yang diperlukan untukpengstabilan dapat diturunkan hampir separuh. Watau bagaimanapun darjah pengaggregatan masih rendah (%pengaggregatan > 2 mm - 5.6%). 1ni mungkin disebabkan kandungan pasir sangat halus dan kelodak adatahrendah iaitu hanya 5.8% dan ketiadaan lempung daln.m tanah pasir bekas lombm'g itu. Hasil kajian inimencadangkan untuk pembaihan struktur tanah pasir bekas lombong dengan menggunakan pembaik tanah,kehadiran juzukjuzuk tanah halus iaitu lempung dan kelodak dan/atau pasir halus datam hadar yang mencukupiadalah sangat perlu. Kehadirannya akan menyebabkan pembentukan stmktur yang kbih baik bagi tanah pasiroleh pemhaik lanah dan seterusnya l1U!71Jebabkan pembaikan ekonomi air dan nutrien lanah itu.

ABSTRACf

The effectiveness of dried palm oil mill effluent (decanter cake), which contains 14 % organic carbon, and ironsolution in promoting aggregation in sand tailing soil was determ;ned. The addition of iron (JT decanter cakeat rates oj 20 and 60 t h«l had no significant effect on the aggregation and stability of the sand. At a higherrate of 100 t h«l, decanter cake gave a significant effect on aggregate stability. With the addition of 0.1 % Fe,the rate of decanter cake application for effective stabilization was reduced to almost half. However, generally theextent of aggregatian was law (% aggregation>2mm was only 5.6%). This could be due to the low amount ofvery fine sand and sil~ amaunting to only 5.8%, and the absence oj clay in the sand tailings. It is postuln.tedthat an improvement in the soil structure of sandy tailings using amendments essentially requires the presence offine soil fractions viz. cln.y and silt and/or very fine sand in suffuient amounts. Their presence will kad to bettersoil structure Jonnation in the sand tailings by the amendments and hence to better water and nutrient economyof the soil.

INTRODUCTION

Large tracts of land are laid waste after tinmining opecations. In 1984, the total hectareageof tin mining lands in Peninsular Malaysia wasapproximately 113,700 ha (Chan, 1990). Eightypercent of this is sand tailings on which it isdifficult 10 establish vegetation because of theabsence of organic matter and the predomi­nance of coarse materials leads to excessive drain-

age, low water and nutrient retention capacitiesand high surface tempecalUres (Lim et al., 1981;Shamshuddin et ai, 1986; Mokhtaruddin andWan Sulaiman, 1990).

Rehabilitation of sand tailings for agricul­ture can be based on three approaches. Theseare: improvement in soil \lIater economy by soilstructurization; raising the fertility status andreducing leaching losses by organic amendments;

A. M. MOKHTARUDDIN AND M. NORHAYATI

and lowering sUlface temperatures by mulching.Structurization can be achieved by adding or­ganic matter. In Malaysia, palm oil mill effluent(POME), of which Malaysia produced about 18million tonnes in 1990. can be a potential sourceof organic matter. POME, if not utilized, cancause environmental pollution. The use of POMEto improve the physical conditions of mineralsoils has been reported by many authors (Lim etal., 1983; Wan Sulaiman et al., 1981) but its useto improve the structure of sandy soil is littlestudied. Besides organic matter, polyvalent met­als such as iron (Fe) are knmvn to promoteaggregation and stability of soils (Deshpande etaL, 1968; Krishna Murti and Rengasamy, 1976).Further Mokhtamddin (1983) showed that inter­action of organic matter and Fe has a synergisticeffect in improving aggregate stability.

The objective of this paper is to evaluate theeffectiveness of POME, alone or in combination\vith Fe, as a soil conditioner to promote soilaggregate formation in sand tailings.

MATERIALS AND METHODS

Soil

Sand tailings used were collected from theUniversiti Pertanian Malaysia tin-tailing researcharea. Particle size distribution was determinedusing the pipette method of Day (1965). Or­ganic carbon content was determined by the wetdigestion method of Walkley and Black (Allison,1965). Free iron oxide was determined by thedithionite-citric-bicarbonate (DCB) method ofMehra and Jackson (1960). Soil pH was meas­ured from 1:2.5 soil/water suspensions. The re­sults are presented in Table 1.

Palm Oil Mill Effluent

The type of POME used was the decanter-driedraw POME (decanter cake). The decanter cakewas analysed for its nutrient and carbon con­tents. Nitrogen was determined by the normalKjeldahl method and P, K, Ca, Mg and Fe by thedry ashing method (Sharifuddin and Dynoodt,1981). The amount of N, P and K was measuredusing an autoanaIyser. and Ca, Mg and Fe withan atomic absorption spectrophotometer. Or­ganic carbon was determined by the wet diges­tion method ofWalk1ey and Black (Allison, 1965).The results are presented in Table 2. Ferroussulphate was used as a source of Fe.

Experimentation

Air-dried sand «2mm, I020 g) in three rep­licates were treated with 0, 10.5. 31.4 and52.3 g of decanter cake which correspondedto an application rate of 0, 20, 60 and 100 tha· l . The sand-decan ter cake mixtures werethoroughly mixed and then sprayed with a0.1 % iron solution (ferrous sulphate) or dis­tilled water (0% Fe) until field capacity.Samples were placed in a plastic bag andincubated for 48 hours at ambienttemperatures. After incubation they were air­dried. The extent of aggregation was evalu­ated by the dry sieving technique. In the drysieving, 100 g of air-dried sample was placedon a nest of sieves with 8.00, 4.75, 2.80, 2.00,1.00, 0.50 and 0.30 mm openings. The sieveswere shaken manually in circular motion tentimes. Aggregates remaining on each sievewere weighed. The extent of aggregation wasexpressed as the fraction of air-dried aggre­gates >2mm (% aggregation> 2mm). Theaggregate stability was determined by the wetsieving technique of Yoder (1936). A 100 g ofair-dried sample «2mm) was placed on a 0.5mm size sieve. The sieve was shaken up anddown in water at a frequency of 40 oscilla­tions per minute for 30 minutes. The heightof oscillations was 4 em. The aggregates re­maining on tht7 sieve were dried and weighed.The aggregate stability was expressed as per­cent water-stable aggregates >0.5mm(%WSA>0.5mm) (Bryan, 1969).

RESULTS AND DISCUSSION

Extent of Aggregation

The sand tailings contain more than 99% sandand trace amounts of clay with negligible veryfine sand and silt fractions (Table 1), which areknmvn to act as the skeleton in aggregate for­mation (Emerson, 1959). This together withthe very low contents of organic matter andfree iron oxides made the sand tailingsstructureless.

Percent Aggregation > 2mm

Percent aggregation of the sand tailings 'was notaffected by the addition of iron or decanter cake(Table 3). Possible causes were (a) the lack ofvery fine sand and silt fractions which hinderthe formation of aggregates, and (b) the inert

84 PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.2 1995

STRUCTIJRAL MODIFICATION OF SA1'1D TAILINGS BY ORGANIC AMENDMENT

TABLE IParticle size distribution and some of thechemical properties of the sand tailings

Content 1.14 0.17 0.99 1.19 0.24 0.139 14.4%

TABLE 2Carbon and nutrient contents of decanter cake

Fraction

Coarse sandMedium sandFine sandVery fine sandClaypHCarbonFree iron oxides

Tr = Trace

Element N p

Size (rom)

> 0.500.25 . 0.500.10 - 0.250.05 • 0.002

< 0.002

K Ca Mg

%

17.436.540.9

0.2Tr5.420.15Tr

Fe C

QUARTZ

Fig. 1: POSJibie !x:mds belWMn clay domains. organic: mat­ter and sand parlicles in an aggregate. Quam­Organic Mauer-Quart, {Q-OM-Ql. {A/terEmer3on, /977{

A Quart'--&ganic Matter-Qua'" (Q:-OM-QIB Qua"'--&gani<: Matler-Cln)' Domain (Q:-OM-C]C Cia)' Domain-Organic: Matter-Polivalent Metal-Clay

Domain (C-OM-P-C]D Cla), Domain Edge-Clay Domain Face fC-C}

nature of the sand tailings. which contained morethan 99% sand, making the iron or decanter cakeineffective in promoting aggregation. Figure 1indicates that although the binding of quartzpartides by organic matter (Q-OM-Q) might havetaken place. the binding seemed weak and couldnOt resist the dry sieving process.

In combination with iron, only the highestrate of decanter cake application (IOO I ha-I )

showed a significant effect on the percent aggre­gation (Table 3).

Percent Water-stable Aggregates >O.5mm(%WSA>O.5mm)

Table 4 shows the effect of iron, decanter cakeand their combination on aggregate stabiltyo As

TABLE 3Comparison between mean percent aggregation of control and treaunems using LSD test

Treaunent

Control0.1% Fe20 t hao

! decanter cake60 t hao

! decanter cake100 t haol decanter cake20 t hao1 decanter cake + 0.1 % Fe60 t hao1 decanter cake + 001 % Fe100 t haol decanter cake + 0.1% FeLSD (5%)LSD (1%)

Mean % aggregationa

4.34.04.04.36.05.75.3

11.3

Difference from contro1b

-o.3n>-0.301

0.30'

1.70 •

1.401

1.0JU

7.0"4.366.05

a Average of 3 replicationsb ** = Significant at 1% le\·el. * = Significant at 5% le\'el, os = Not significant

PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.2, 1995 85

A M. MOKHTARUDDIN AND M. NORHAYATI

TABLE 4Comparison between mean percent WSA > 0.5 mm of control and each of the treatments using LSD test

Treaunent

CoIlU·ot0.1% Fe20 t ha·1 decanter cake60 t ha-' decanter cake100 t ha-1 decanter cake20 t ha-' decanter cake + 0.1 % Fe60 t ha-' decanter cake + 0.1 % Fe100 t ha'\ decanter cake + 0.1 % FeLSD (5%)LSD (1 %)

Mean % aggregation> 2 mm~

23.321.723.024.733.027.333.333.7

Difference from conrrolb

1.6'".Q.3'"l.4ru

9.7""4.0m

10.0"lOA'·6.559.09

;I Average of 3 replicationsb ** = Significant at 1% level, * = Significant at 5% level, os "'" NO( significam

with percent aggregation, aggregate stability wasnot significantly affected by the addition of Fe.The addition of decanter cake at the rate of 20and 60 t ha·' slightly increased the stability of theaggregates but the increase was not significant. Atthe highest rate of 100 t ha·1

, decanter cake gavea significant increase in aggregate stability. This isin accordance with the known fact that organicmatter in adequate amounts is needed for theformation of water-stable aggregates. In combina­tion with iron, the higher rates of decanter cakeapplication (60 and 100 t ha·') gave a significantincrease in the aggregate stability but the lowestrate of 20 t ha·' did not. It appears that theaddition of 0.1 % Fe was able to reduce theamount of decanter cake required for effectivestabilization implying that the interaction of ironand organic matter was partly responsible in ag­gregate stabilization in sandy soils. Giovanniniand Sequi (1976) suggested that iron fonns blidg­ing between organic polymers (-OM-P-OM-),wbich binds the sand particles more strongly.

The above findings suggest that the combi­nation of decanter cake and iron has a greatereffect than the decanter cake or iron alone onthe stability of aggregates in sandy tailings. How­ever, the overall extent of aggregation resultingfrom this treatment was still low (average %aggregation> 2mm is 5.6%, Table 2). Previouswork has demonstrated a similar effect in thatthe addition of organic amendments to sandysoils failed to give positive response to the aggre­gation and stability of these soils (Lim et aL,1983; Othman el al., 1990). On the other hand,

when similar experiments were carried out onmineral soils, a significant increase in aggrega­tion and stability was noticed (Mokhtaruddin,1983; Mokhtaruddin and Wan Sulaiman, 1987).

Figure 1 clearly shows that for good aggre­gation in the sand tailings, the presence of clay,silt and very fine sand fractions is indispensible.Clay particles is a well knmvn cementing mate­rial binding the skeletal materials, such as veryfine sand, together into aggregates (Peterson,1946; Kemper and Koch, 1966; Dixon, 1991).

CONCLUSION

Iron and organic matter are known as excellentaggregating and stabilizing agents in soils.Nevertheless,this smdy shows that the additionof iron or decaotered dried raw POME (de­canter cake) at 20 and 60 t ha·' to the sandtailings (which complised more than 99% sand)had no effect on aggregation and stability. Athigher rates (100 t ha·'), decanter cake had apositive effect 00 aggregate stability. In combi­nation with iron, the rate of decanter cakeapplication can be reduced to 60 t ha- I foreffective stabilization. However, the overall ex­tent of aggregation resulting from the lattertreatment was low (% aggregation > 2mm =

5.6%). The most probable explanation was thelack of very fine sand and silt fractions, whichact as skeleton in the formation of aggregates,and the absence of claro which interacts withorganic polymer and polyvalent metal to form astrong bond. It is therefore postulated that thepresence of fine fractions in sufficient quantity

86 PERTANlKAJ. TROP. AGRIC. SCI. VOL. 18 NO.2 1995

STRUCTURAL MODIFICATION OF SAND TAILINGS BY ORGANIC AMENDMENT

is a prerequisite for soil structure improvementor development in sand tailings using amend­ments.

ACKNOWLEDGEMENT

The authors would like to record their utmostappreciation to Universiti Pertanian Malaysia andNational Council for Scientific Research andDevelopment of Malaysia for financial and tech­nical support under the Intensification of Re­search Priority Areas (IRPA) Project No: 1-07-05­

048 002).

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(lUceiv,d 31 januar)' 1994; accepted 22 May 1995)

88 PERTANlKAJ. TROP. AGRlC. SCI. VOL. 18 NO. 2 1995