沙漠研究 19-1, 343- 346 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

The Olive Mills Waste Water (OMW) as an Organic Amendment for ControllingWind Erosion in Southern Tunisia by Improving the Soil Surface Structure
M. ABICHOU1, M. LABIADH2, W. CORNELIS3, D. GABRIELS3,B. BEN ROUINA1, H. TAAMALLAH2, H. KHATTELI2
Abstract: Spraying OMW on poor sandy soils in the olive orchards induces increasing of theorganic matter content, the formation of aggregates and improving the soil structure stability.
Hence, OMW can be an alternative and effective way to control this polluting sewage. Since
1995 a field experiment is running in an olive plot in chammakh-Zarzis, south Tunisia, whererates of 50, 100 and 200 m3 of OMW were sprayed yearly on 1 ha fields with 16 olives trees per
ha. Data collected in 2006 showed an increase in organic matter content from originally 0.06 to
1.27 %, an increase in the amount of aggregates > 2 mm to 34%, and an increase in thethreshold friction velocity for deflation to 12 m sec-1 for the 200 m3 ha-1 application.
Key words: Aggregates, Friction velocity, Olive mills waste water, Organic matter, Tunisia

1. Introduction
Soil degradation especially related to detoriation of its physical properties is a common problem insouthern Tunisia. One of its most appearent manifestations is the surface crust formation and the reductionof the vegetation cover due to water and wind erosion. Increasing the organic matter content in sandy soils
can increase the aggregate formation and stability and reduce its vulnerability to erosion.
The quantities of Olive Mills Waste water, accumulating each year and dumped in open reservoirs
and lakes; constitute also a real environmental problem in Tunisia. They can be used as an organic
amendment for improving soil physical properties (Mellouli, 1996). The main chemical characteristics ofthis sewage are reported in Table 1.
The objective of this study is to evaluate the impact of 10 years of successive OMW sprays on thesurface properties of sandy soils in olive orchards in southern Tunisia. This work is a joint venture of theInstitut de l’Olivier, Zarzis, Tunisia, The institut des Régions Arides, Médenine, Tunisia and the Unesco
Chair on Eremology, Ghent University, Belgium, And SOPHIU, Soil Erosion and Soil Physics ResearchGroup of the Department of Soil Management, Ghent University, Belgium.
2. Materials and methods
2.1. Study zone
The study zone is located at Chammakh-Zarzis in the south eastern Tunisia. The climat of this region
is an arid Mediterranean climate with an annual average rainfall of 180 mm (i.e. long term average for theperiod 1923-2004). The soil of this area is moderately deep with a slight texture, very filterable andrelatively poor in organic matter.
2.2. Methodology
2.2.1. On site Application of the OMW
The OMW spray is insured by an empty pit citern manipulated by a tractor takeover power. TheOMW is homogeneously spread on the soil with the respective doses of 50 m3/ha, 100 m3/ha and 200
m3/ha.
Table 1. Chemical characteristics of OMW (the major elements).

1Elements

H (%)

pH waterCe(mS/cm)

M matter(g/l)

K (g/l)O. matter
(g/l)

Value

87,9

5,518,613,77,5107,0Institut de l’Olivier Station de zarzis, 4170, TUNISIA;
Institut des Régions Arides, Médenine,4119, TUNISIA;
3
Faculty Bioscience engineering, Coupure links nr 653, B-9000 Gent
2Reducingsugar(g/l)
11,4Phenols (g/l)
5,8

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Another field called witness field remains without any treatment (0 m3/ha)). The treatments wereapplied for 10 years: since 1996 till 2006 during the month of January. Each treated plot covered a surface
of one hectare (16 olive trees in full production and aged between 60 to 70 years) and separated by 2 nontreated olive trees rows (48 m) .
2.2.2. Monitored parameters2.2.2.1. The Organic matter
The organic matter rate was determined by Walkley and Black methods which consisted on coldoxidization with bichromate of potassium (K2Cr2O7) in acid environment and titration with ferrous sulfate(FeSO4,7H2O). The organic matter rate was calculated by the fellow equation:
MO% = C% x 1.725
2.2.2.2. Aggregate and structural stability
The OMW effects on soil structural stability were determined in laboratory for three doses (50, 100,200 m3/ha). The stability is expressed as a difference in status of the soil before (initial status) and after(final status) a force is applied. Therefore it is necessary to assess the initial and final status of theaggregates. Soil aggregates have different sizes (diameter) and the aggregate size distribution (expressedin % of the different diameter fractions) can fit a log-normal distribution. The aggregate size distribution
can be characterised by the mean weight diameter MWD.
To determine the structural stability we should:
1. calculate the mass of the rain drop.
2. calculate the MWD after dry (MWDd)and after wet (MWDw) sieving∑m d
MWD =Where mi = mass of aggregate fraction I,∑mdi = mean diameter of fraction I,
3. calculate the instability index (IS) using following expression :1
si =IS = MWDdz - MWDnz
IS
4. calculate the instability index (IS) using following expression :5. plot the aggregate size distribution after dry and after wet sieving.
2.2.2.3. Threshold friction velocity
Laboratory wind tunnel simulations have been carried out to study the effect of wind erosion on atreated surface where different doses of OMW were spread in the upper soil layer (0 m3/ha, 50 m3/ha, 100m3/ha and 200 m3/ha). For each treatment we had determined the threshold friction velocity u*t using
Cornelis and Gabriels methods (Cornelis and Gabriels, 2004) in the International Centre for Eremology(I.C.E). The I.C.E wind tunnel simulator used is the one described by Cornelis et al. (2004). It is a closed
circuit blowing –type wind tunnel with a 12m long, 1.2 m wide and 3.2 m high working section (Gabrielset al., 1997). The boundary layer was set at about 0.60 m using a combination of spires and roughness
elements (Cornelis, 2002).
For the static Analysis, we have used the STATGRAPHICS Plus 5.1. LSD test was used to find any
significative difference between treatment means.
i=ni =1i=ni =1iii

3. Results and Discussions
3.1. Organic mater
When the organic matter is injected in the soil, its structural stability is directly affected first becauseof the immediate physico-chemical changes (abiotic factors), then, again during the decomposition of theorganic matter brought by micro-organisms activated by the sugar (source of energy) present in the OMW(biologic factors). Rich in organic substances (107 kg/m3), the OMW spray improved the content of soil inthese substance. Indeed, the organic matter rate, initially very weak (0.06), raised to 0.41%, 0.71% and1.27% respectively for the doses of 50 m3 / ha, 100 m3/ha and 200 m3/ha after ten successive years ofOMW spray (Table 2). Therefore, the organic matter rates increase is proportional to the applied doses.
The differences observed could be explained by the kinetics of the organic matter mineralization process
which depends on the quality and quality of micro-organisms in the treated soil. Similar results wereobtained by Cabrera et al. (1996) who indicate that the yearly supply, during three years, of 37 l/m² or 61
l/m² of OMW, on sandy soil with an initial organic matter rate of 0.45 %, could increase the organic matter345

Table 2. Evolution of organic matter rate after 10 years of OMW spray.
Doses
Mean

T00.35 ± 0,12T10,49 ± 0,13a

T20,60 ± 0,21ab

T31,05 ± 0,28bc

Table 3. Aggregate and Structural stability.
Doses% Aggregate > 2mm

T1
7,32 ± 1,45

T212,78 ± 3,17ab

100
Cumulative masspercentage (%)

Cumulative masspercentage (%)

100T333,93 ± 5,73a80
60
40
2080

60

40

2000246800

Aggre gate s ize (m m )2468

Aggre gate size (mm)Dry sieving

Wet sieving

Dry sieving

3-1Fig. 1. Aggregate size after spreading 50 m ha .

Wet sieving

Fig. 2. Aggregate size after spreading 100 m3 ha-1.

Cumulativemasspercentage(%)

10080604020002468Aggre gate size (mm)Dry sieving

Wet sieving

Fig. 3. Aggregate size after spreading 200 m3 ha-1.

content respectively to 1.62% and 1.98%. Organic amendment supply represented the principal cohesion
factor between the soil aggregates. This observation is in agreement with results given by Oades (1993)
and Angers and Cover (1996).
3.2. Aggregate and structural stability
It was only at rates of 200 m3 ha-1 that differences in aggregate formation could be found. In thelower rates (50 and 100m3 ha-1) only 10% of the aggregates had diameters larger than 2 mm, at the 200 m3
ha-1 rate, 35% of the aggregates had diameters larger than 2mm (Table 3).
The same samples were under water sieving test and allowed to break down. Once more the 200 m3-1
ha rate showed important differences compared to the lower application rates, where only 5% ofaggregates had diameters bigger than 2mm. The 200 m3 ha-1 application rate on the other hand still
resulted in 25% of aggregates with diameters larger than 2mm, reflecting also a higher aggregate stability(Figures 1, 2 and 3).
3.3. Threshold friction velocity
These results showed that the threshold velocity was raised with doses of OMW spray. These velocities
are respectively 8.50 m/s and 12.5 m/s for 0 m3/ha and 200 m3/ha (Table 4). Therefore, wind erosion inorchard olive tree could be reduced. These results could be explained, by the increase of the organic matter.
The same results are obtained by Mellouli (1996), Ben Rouina and Taamallah (1999) and Abichou (2003).
They showed that OMW improve the mulch formation which can reduce water and wind erosion. Statisticalanalysis showed no significant difference between T0 and T1 but it was a high significant with T3.

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Table 4. The threshold friction velocity values.
Doses
Mean

T0
8,50 ± 0,15a

T1
8,65 ± 0,17a

T2
10,25 ± 0,16b

T3
12,15 ± 0,93c

4. Conclusion
A successive spreading of OMW in sandy soil, with doses bellow 200 m3/ha, is without negative
effect and induces a soil conglomeration thanks to its high content in organic matter. The organic matter
rate increases the cementation of the soil aggregates. Therefore, the structural stability is improved andwind erosion is reduced. These results can be compared to those of Gabriels et al. (1975) obtained insandy soil showing the efficiency of mulch constituted by the aggregate inferior to 5.5mm in thickness
permitting therefore a better stability of soil and a substantial reduction of evaporation.
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