Materials, Methods and Results

2. Materials, Methods and Results

2.1 Field Applications The Chammakh-Zarzis olive orchard is situated in

southern Tunisia (Fig. 1) in an environment with an arid Mediterranean climate with a mean annual rainfall of 180 mm, as long-term average for the period of 1923-2004. The soil is moderately deep with a sandy texture and poor in organic matter [2].

The “margine” is pumped from a pit cistern in a tank and brought by tractor to the field (Fig. 2). Then it is

sprayed homogeneously on the sandy soil surface,

Fig. 2 “Margine” spray from tank and tractor.

The Mulching Effect of the Olives Mill Wastewaters on the Soil Cohesion Improvement and Wind Erosion Reduction in the Southern Tunisian Arid Zones

abounding, in number and quality, of microorganisms in the treated soil. Similar results were obtained by F. Cabrera et al. [3] who showed that after three successive years of “margine” applications rate of 37

3 L/m² (370 m 3 /ha) and 61 L/m² (610 m /ha) organic matter content up to 1.62% and 1.98%, respectively.

Organic amendment supply represented the principal cohesion factor between the soil aggregations. This observation is in agreement with results given by

Oades, Angers, et al. [4, 5].

Fig. 3 “Margine” treated parcel.

2.2.2 Aggregate Formation and Stability

2.2 Experiment Results and Discussion Disturbed surface samples were taken and brought to the laboratory. Previously air-dried samples were

2.2.1 Organic Matter Content sieved and the dry aggregate distribution determined.

The organic matter rate was determined by Walkley It was only at rates of 200 m 3 /ha that differences in

and Black methods which consisted on cold oxidization with bichromate of potassium (K Cr O ) in

aggregate formation could be found. As at lower rates

acid environment and titration with ferrous sulfate of applications (50 and 100 m /ha) only 10% of the (FeSO 4 ·7H 2 O). The organic matter rate was calculated

aggregates had diameters larger than 2 mm, at the 200

by the followed Eq. (1): m /ha rate 35% of the aggregates had diameters larger MO% = C% × 1.725

than 2 mm.

Soil samples for organic matter content The same samples were then subjected to a under determination were taken in 2006 on each parcel and

water sieving test and allowed to break down. When this after 10 years of “margine” application. The

aggregates are submerged in water and gently sieved organic matter content is listed in Table 2.

under water (wet sieving), their status will change Rich in organic substances (107 kg/m 3 ), the

compared to their initial status (dry aggregates). Hence, mulching of OMW improved the soil organic matter

the difference in mean diameter of the aggregates rates. Indeed, the differences observed could be

before (dry) and after (wet) sieving can be used as the explained by the kinetics of the organic matter

in stability index IS. The difference of the areas mineralization process, which depended on the under the curves of dry and wet aggregate distribution

Fig. 4 Schematic plan of Chammakh -Zarzis experimental parcel.

The Mulching Effect of the Olives Mill Wastewaters on the Soil Cohesion Improvement

and Wind Erosion Reduction in the Southern Tunisian Arid Zones

Table 2 Organic matter content of the upper sandy soil layer after 10 years of “margine” application.

80 / a

Doses (m 3 ha)

Organic matter content (%)

e(

0 (control) tag 0.06 3

100 0.71 as 40 200 1.27 ive m

lat

describes this stability.

Generally, the inverse of IS, the stability index SI is

Aggregate size (m m )

taken as a measure for the stability of the soil

Dry sieving

Wet sieving

aggregates. The higher is the value, the more stable are

the aggregates. 100

To determine the structural stability we should: ) %

80 b

1. Calculate the mass of the raindrop.

tag

rcen e 60 2. Calculate the mean weight diameter after dry MWD 3

100 m /ha

and after wet MWD ass w sieving:

ve m ti

la  u

1 (2) 20 C

MWD 

where m Aggregate size (mm)

i = mass of aggregate fraction i; d i = mean

diameter of fraction i. Wet sieving

Dry sieving

3. Calculate the instability index (IS) using following

4. Calculate the stability index (SI) using following en

e rc

200 m /ha

expression: a

5. Plot the aggregate size distribution after dry and after

0 2 4 6 wet sieving. 8

3 Aggregate size (mm)

Once more the 200 m /ha rate showed marked

Dry sieving

Wet sieving

differences compared to the lower application rates,

Fig. 5 Mulching effect of OMW in structural stability.

where now only 5% of the aggregates had diameters larger than 2 mm. The 200 m 3 /ha application rate on the

presence of water, the soil could be structured but it is other hand still resulted in 25% of aggregates with

stability depended on it is contain of clay and loam diameters larger than 2 mm, reflecting also a higher

both considered as an enduring cohesion factors [6]. aggregate stability (Fig. 5).

The same results are obtained on the sandy soil These results are in concordance with the Mellouli’s

treated by the compost [7]. This technique of results who concluded that it is possible to improve the

mulching could improve the soil stability and reduce stability of an unstable soil (loamy soil). Indeed, in

the evaporation.

The Mulching Effect of the Olives Mill Wastewaters on the Soil Cohesion Improvement and Wind Erosion Reduction in the Southern Tunisian Arid Zones

2.2.3 Threshold Friction Velocity for Initiating

Table 3 Threshold friction velocities for initiating particle

Particle Movement movement after 10 year of “margine” application.

Bulk samples of the upper sandy soil layers were Threshold friction velocity (m/s)

Doses (m 3 /ha)

0 (control)

shipped to the Department of Soil Management of 50 8.65

Ghent University, Belgium to be tested in the wind 100 10.25

tunnel of the International Center for Eremology (ICE). 200 l2.15

The wind tunnel of ICE is described in detail [8, 9].

The boundary layer was set at about 0.60 m using a raised with doses of OMW spray. These velocities are combination of spires and roughness elements [10]. 3 respectively 8.50 m/s and 12.5 m/s for 0 m /ha and 200

The samples were placed in 0.95 × 0.40 × 0.02 m trays 3 m /ha (Table 3). and put at a distance of 6.00 m downwind from the

These results could be explained, by the entrance of the wind tunnel working section. To ensure

augmentation of organic matter. The same results are wind tunnel profile equilibrium with the roughness of

obtained [13-15]. They showed that OMW with it is the sample surface, the test section was covered with

link power improve the mulch formation which can commercially available emery paper with the same

reduce water and wind erosion.

roughness length as the surface of the sample, as

2.2.4 Natural Floristic Composition for Soil determined experimentally from measured wind Roughness Improvement velocity profiles [11].

The mulching effect of OMW in the vegetation Wind at different reference velocities u ref (recorded

cover and natural floristic composition had been at a height of 1.00 m at the entrance of the test area)

investigated when we had observed a visual difference were introduced in the test area and wind velocities u

on the invading yearly species. Indeed, some species as were monitored at a 1 Hz frequency with 13 mm

Chenopodia murale and Mesembryanthemum diameter vane probes mounted at heights of 0.05 m,

cristallinum which they had never been founded in the 0.l0 m, 0.15 m, 0.20 m, 0.30 m, 0.40 m, 0.50 m, 0.60 m

witness parcels and those surrounding had founded for and 0.70 m. The shear velocity u *t of the sand surface

the other parcel treated with “margine”. The Presence could be calculated from the wind profile and the

Specific Contribution (CSP) of these two species was roughness length z 0 and the Von Karman constant k 0.4

53% and 37% respectively (Fig. 6). (Eq. 5).

These results could be explained by the ecological

and biological feature of these species which tolerate u z 

ln

z 0 an important quantity of nitrates and salts in soils The initiation of particle movement was determined

(elevated electric conductivity in the parcel treated by continuously recording particle transport with a 3 with 200 m /ha).

saltiphone”. The “saltiphone” is an acoustic sensor that Nevertheless, the density of Diplotaxis harra is records the number of saltating particles that bounce 2 relatively abundant (18 individual/m ) in the witness

against a microphone at a frequency of 0.1 Hz [12]. parcel where the CSP is 11%. However, the density of To determine the threshold friction velocity u *t for

this specie is nil in the parcel treated with the dose of initiating particle movement, the u 3

200 m /ha. These effects could be explained by the until first particles were recorded with the saltiphone

ref was increased

seeds germination inhibition caused by the high dose of [9]. Table 3 illustrates the threshold friction velocity

“margine”. Indeed, the acidic pH and the presence of values for the different treatments with margine.

phenolic composed seems be very aggressive on some These results showed that the threshold velocity was

sensitive species.

The Mulching Effect of the Olives Mill Wastewaters on the Soil Cohesion Improvement

and Wind Erosion Reduction in the Southern Tunisian Arid Zones

50m 3 50m 3/ /h ha 100m 3 /h a

200m 3 /h a

Dose (m3/ha) ( m 3/ ha )

Loblaria libyea

Diplotaxis Harra

Enarthrocarpus clavatus

Cutandia dichotima

Chenopodia murale

Me sembryanthemum cristallinium

Launaea glomerata

Fig. 6 Natural floristic composition.

According to these results, we can conclude that the OMW on the natural floristic composition. According mulching of OMW in the abandon and pastoral area

to these results, the spontaneous vegetation acts at could be beneficial to control the messicoles annual

lower scale as an erodibility factor, determining species development. In most cases, the fallow lands

resistance or vulnerability to erosion. At contiguous but are dominated by Diplotaxis harra, which is a very

higher scale cover factors becomes erosivity factors, weak economic value species (pastoral, medicinal or

structurally mediating erosive energy of wind. Hence, other). Therefore, it seems that the “margine” could

“margine” can be an alternative and effective way to decrease the competition of this species to the profit of

control wind erosion in southern Tunisian arid zones. others which should be more beneficial as well as

References

pastoral and industrial plan like the Mesumbryanthemum cristallinium , species used for

[1] E. Bonari, L. Ceccarini, Sugli effete dello spargimento dell acque di vegetazione sul terreno afrario: Risultati di una

soap manufacture. ricerca sperimentale, Genio Rurale 5 (1990) 60-67. (in

Italian)