Soils In Tunisia Research Articles

Possibility of using RIT technology in the ground conditions of Vietnam

The article compares engineering and geological conditions in the coastal areas of Vietnam and Tunisia. A sufficiently high similarity of soil structure and their physical and mechanical properties was noted. Both in Vietnam and in Tunisia, foundations for responsible buildings and structures are arranged on bored piles of the same length of 40-60 meters and a diameter of 600 to 1600 mm. The article provides examples of using super-piles of small-size RIT using recharge impulse technology in conditions of weak water-saturated coastal soils of Tunisia. The high efficiency and cost-effectiveness of the new recharge impulse technology were noted. The article presents photographic materials of the test stand for conducting field tests of piles, presents and analyzes the results of testing piles with vertical static load. The low precipitation of the tested piles and their high load-bearing capacity prove the promise of using super-piles of RIT in the conditions of weak soils of Tunisia and, consequently, in the coastal areas of Vietnam.

Comparative Study of Soil Tillage Practices Effects on Hydraulic Conductivity and Bulk Density of a Sandy Loam Soil in Tunisia

The aim of this study was to investigate the effects of different tillage practices on bulk density, and the hydraulic properties of a sandy loam soil of eastern Tunisia. A replicated randomized complete block design with treatments consisting of (i) no-tillage (NT), (ii) tillage with moldboard plow at three level depths (SM=15cm, MM=20cm and DM=25cm), (iii) and tillage with disc plow at three level depths (SD=15cm, MD=20cm and DD=25cm) practices established at the Higher Institute of Agricultural Sciences of Sousse; Tunisia was used for the study. The soil bulk density and saturated hydraulic conductivity were determined for each of the treatments. The bulk density (BD) was determined at the depths of 5, 15 and 25 cm while the saturated hydraulic conductivity was determined on the surface (0-10 cm) soil. Experimental results showed that all the tillage practices were significantly different in their effects on soil density and was in the descending order of NT>SD> MD>DD>SM>MM>DM. The soil bulk density decreased with the degree of soil manipulation during tillage practices, with NT having the highest (1.76; 1.86 and 1.81g cm-3) and DD having the least (1.60; 1.56 and 1.59g cm-3) respectively for 5, 15 and 25cm depths. The greater mean value of Ksat was found in DD while the lowest was found in NT with 36% reduction than DD. The research concluded that the best Tillage Practices to be adopted in terms of improvement in physical and hydraulic properties is Shallow tillage practice.

Purification and characterization of a fungal laccase from the ascomycete Thielavia sp. and its role in the decolorization of a recalcitrant dye

A laccase-producing ascomycete was isolated from arid soil in Tunisia. This fungus was identified as Thielavia sp. using the phylogenetic analysis of rDNA internal transcribed spacers. The extracellular laccase produced by the fungus was purified to electrophoretic homogeneity, showing a molecular mass around 70 kDa. The enzyme had an optimum pH of 5.0 and 6.0 for ABTS and 2,6‑DMP, respectively and it showed remarkable high thermal stability, showing its optimal temperature at 70 °C (against 2,6‑DMP). It presented slight inhibiting effect by EDTA, SDS and l‑cyst although this effect was more marked by sodium azide (0.1 mM). On the other hand, it showed tolerance to up to 300 mM NaCl, retaining around 50% of its activity at 900 mM. Among the metal ions tested on TaLac1, Mn2+ showed an activating effect. Their kinetic parameters Km and kcat were 23.7 μM and 4.14 s−1 for ABTS, and 24.3 μM and 3.46 s−1 towards 2,6‑DMP. The purified enzyme displayed greater efficiency in Remazol Brilliant Blue R decolorization (90%) in absence of redox mediator, an important property for biotechnological applications.

Antimicrobial Activities of Some Actinomycetes Isolated from Different Rhizospheric Soils in Tunisia.

Fifty four isolates of actinomycetes were collected from four different rhizospheric soils: 18 strains from palm tree bark and soil, 12 strains from an olive field soil, 9 strains from a coastal forest, and 15 strains from an agriculture soil situated in the Algerian-Tunisian border (Oum Tboul). Based on morphological and cultural characters, the isolates were classified as Streptomyces (42 strains), Micromonospora (4 strains), Pseudonocardia (1 strain), Actinomadura (1 strain), Nocardia (1 strain), and non-Streptomyces (5 strains). More than half of the isolates inhibited at least one tested pathogenic microorganisms in liquid culture. In addition, antimicrobial activities of some strains were tested on solid culture. Several bioactive compounds were identified by liquid chromatography joined with low-resolution mass spectroscopy (LC/MS) and analysed by MEDINA's database and by the dictionary of natural products Chapman & Hall. An interesting chlorinated compound with the molecular formula C20H37ClN2O4, produced by three different strains (SF1, SF2, and SF5), was subject of an attempted purification. However, it was demonstrated using confocal microscopy and LC/MS high resolution that this compound is produced only on solid culture. These three potential antimicrobial isolates showed high similarity with Streptomyces thinghirensis and Streptomyces lienomycini, in terms of morphological characteristics and 16S rRNA gene sequences (bootstrap 97%). All these findings prove the high antimicrobial diversity of the studied soils. The potential of the selected and other relatively unexplored extreme environments constitute a source of interesting actinomycete strains producing several biologically active secondary metabolites.

Feasibility of a Bioremediation Process Using Biostimulation with Inorganic Nutrient NPK for Hydrocarbon Contaminated Soil in Tunisia

This study focused on the processing time reduction of soils microcosm process, during the biological restore of diesel-contaminated soil under natural conditions. Biodegradation activity of hydrocabonoclastic microflora and biostimulation with inorganic nutrient (NPK) were studied through the determination of optimal conditions which improve bioremediation process. Indeed, after 56 days, about 98% removal rate of total petroleum hydrocarbon (TPH) in soil treated by microcosm’s technique were observed relative to approximately 2.22×107CFU/g soil of bacterial number. This performance was achieved with microbial (bacteria) metabolism which accompanies biodegradation of hydrocarbons. Moreover, the hydrocarbon fractions (alkanes and aromatics) were rapidly degraded then the other complex fractions according to GC/MS and FT-IR analysis

Fingerprinting sediment sources in the outlet reservoir of a hilly cultivated catchment in Tunisia

Approximately 74 % of agricultural soils in Tunisia are affected by water erosion, leading to the siltation of numerous human-made reservoirs and therefore a loss of water storage capacity. The objective of this study was to propose a methodology for estimating the relative contributions of gully/channel bank erosion and surface topsoil erosion to the sediment accumulated in small reservoirs. We tested an approach based on the sediment fingerprinting technique for sediments collected from a reservoir (which has been in operation since 1994) at the outlet of a catchment (Kamech, 2.63 km2). Sampling concentrated on the soil surface (in both cropland and grassland), gullies and channel banks. A total of 17 sediment cores were collected along a longitudinal transect of the Kamech reservoir to investigate the origin of the sediment throughout the reservoir. Radionuclides (particularly caesium-137, 137Cs) and nutrients (total phosphorus, total nitrogen and total organic carbon (TOC)) were analysed as potential tracers. The applications of a mixing model with 137Cs alone or 137Cs and TOC provided very similar results: The dominant source of sediment was surface erosion, which was responsible for 80 % of the total erosion within the Kamech catchment. Additionally, we showed that the analysis of a single composite core provided information on the sediment origin that was consistent with the analysis of all sediment layers in the core. We demonstrated the importance of the core sampling location within the reservoir for obtaining reliable information regarding sediment sources and the dominant erosion processes. The dominance of surface erosion processes indicates that conservation farming practices are required to mitigate erosion in the agricultural Kamech catchment. Based on the results from 17 sediment cores, guidelines regarding the number and location of sampling cores to be collected for sediment fingerprinting are proposed. We showed that the collection of two cores limited the sediment source apportionment uncertainty due to the core sampling scheme to <10 %.

Taxonomic and symbiotic diversity of bacteria isolated from nodules ofAcacia tortilissubsp.raddianain arid soils of Tunisia

A collection of rhizobia isolated from Acacia tortilis subsp. raddiana nodules from various arid soils in Tunisia was analyzed for their diversity at both taxonomic and symbiotic levels. The isolates were found to be phenotypically diverse. The majority of the isolates tolerated 3% NaCl and grew at 40 °C. Genetic characterization emphasized that most of the strains (42/50) belong to the genus Ensifer, particularly the species Ensifer meliloti, Ensifer garamanticus, and Ensifer numidicus. Symbiotic properties of isolates showed diversity in their capacity to nodulate their host plant and to fix atmospheric nitrogen. The most effective isolates were closely related to E. garamanticus. Nodulation tests showed that 3 strains belonging to Mesorhizobium genus failed to renodulate their host plant, which is surprising for symbiotic rhizobia. Furthermore, our results support the presence of non-nodulating endophytic bacteria belonging to the Acinetobacter genus in legume nodules.

Impact of grazing on soil microbial communities along a chronosequence of Acacia tortilis subsp. raddiana in arid soils in Tunisia

Acacia tortilis (Forssk.) subsp. raddiana (Savi) Brenan is a woody legume recommended for adoption in arid lands of Tunisia, but their grazing is recognized as one of the main causes of soil degradation and desertification in these areas. The aim of this research was to explore the effects of grazing intensity on soil properties under A. tortilis subsp. raddiana along a chronosequence of young, mid-aged and old trees. Soil chemical, microbial and biochemical properties were evaluated. The results showed that tree growth increased soil pH, electrical conductivity, soil organic carbon (Corg), microbial biomass carbon (Cmic), Cmic:Corg ratio and enzyme activities (dehydrogenase, phosphatase and β-glucosidase). In contrast, C:N ratio and metabolic quotient (qCO2) decreased with increasing tree age. For the impact of grazing intensity, the amount of organic matter, microbial biomass and enzyme activities were reduced in intensively grazed site, while C:N ratio and metabolic quotient were higher.The findings demonstrated significant impacts of Acacia age-classes and grazing intensity on soil properties. It is concluded that A. tortilis subsp. raddiana establishment and development enhanced the development and the activity of microbial communities in soil; however, intensive grazing was detrimental to soil quality. This indicates that A. tortilis subsp. raddiana improved soil quality and play an important role in soil protection of degraded lands in Tunisia.

Identification and partial characterization of antifungal and antibacterial activities of two Bacillus sp. strains isolated from salt soil in Tunisia

Two Bacillus sp. strains (B29 and B27) isolated from soil in the South of Tunisia were tested for their abilities to produce antimicrobial compounds. Both strains showed antimicrobial activity against Gram-positive and Gram-negative bacteria, yeasts and fungi. The produced compounds were extracted by using four different solvents. The hexane solvent allowed to obtain maximum of activity of the strain B29. The activity of the strain B27 was not elucidated by the four solvents used. Bio-autography results of B29 hexane extract revealed presence of different antibiotics and antifungal compounds with different Rf values of 0.3 and 0.76 for antifungal compounds and of 0.12, 0.14, 0.19 and 0.3 for antibacterial ones. Two active fractions were isolated from the culture broth of the strain B29 by semi-preparative high performance liquid chromatography (HPLC). The partial sequencing of the 16S rDNA gene was used to identify the two Bacillus strains. They may be assigned to new Bacillus species

Characterization of root-nodulating bacteria associated to Prosopis farcta growing in the arid regions of Tunisia

Diversity of 50 bacterial isolates recovered from root nodules of Prosopis farcta grown in different arid soils in Tunisia, was investigated. Characterization of isolates was assessed using a polyphasic approach including phenotypic characteristics, 16S rRNA gene PCR--RFLP and sequencing, nodA gene sequencing and MLSA. It was found that most of isolates are tolerant to high temperature (40°C) and salinity (3%). Genetic characterization emphasizes that isolates were assigned to the genus Ensifer (80%), Mesorhizobium (4%) and non-nodulating endophytic bacteria (16%). Forty isolates belonging to the genus Ensifer were affiliated to Ensifer meliloti, Ensifer xinjiangense/Ensifer fredii and Ensifer numidicus species. Two isolates belonged to the genus Mesorhizobium. Eight isolates failing to renodulate their host plant were endophytic bacteria and belonged to Bacillus, Paenibacillus and Acinetobacter genera. Symbiotic properties of nodulating isolates showed a diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Isolate PG29 identified as Ensifer meliloti was the most effective one. Ability of Prosopis farcta to establish symbiosis with rhizobial species confers an important advantage for this species to be used in reforestation programs. This study offered the first systematic information about the diversity of microsymbionts nodulating Prosopis farcta in the arid regions of Tunisia.

Land use effect on soil and particulate organic carbon, and aggregate stability in some soils in Tunisia

Conversion of native forests to cultivation is usually accompanied by a decline in soil organic carbon and nutrients, and deterioration of soil structure. Our knowledge of this process must increase if we are to optimise the physical regeneration of degraded soils in semiarid areas. In this work we aim to (i) determine the relationship between aggregate stability and soil and particulate organic carbon (ii) to study the evolution of this relationship with land use. Samples were collected from a cropland cultivated and an adjacent natural forest and pasture from tree toposequence in North Tunisia. Change in land use from forest soil to pasture and cultivation induced significant losses of soil and particulate organic carbon. The soil organic carbon loss from forest soils to agriculture soils reached 83 and 74% from forest soils to pasture lands. However, the average of particulate organic carbon in forest ranged from 15 to 27 g kg-1 and 3 to 14 g kg-1 in agriculture soils. Across 13 sites, the average of mean weight diameter significantly decreased from (2.79 mm) natural forest soil to (2.10 mm) to pasture soil, being more significant in the cultivation soil (1.70 mm). Fast wetting treatment, causing aggregate slaking, was the process that decreased aggregate stability the most. Significant correlation was found between aggregate stability and soil organic carbon fraction. However, the greater association was observed between aggregate stability and particulate organic carbon. Soil where the organic matter was the principal aggregation agent (soil with sandy texture and zero carbonate calcium content) showed greater degradation sensitivity to soil organic carbon loss. Soil aggregate stability and soil organic carbon fraction could be used as indicators to apply the most appropriate management practices to increase soil sustainability or productivity. Key words: Land use, soil organic carbon, particulate organic carbon, aggregate stability, North Tunisia.

Soil Organic Carbon Fractions and Aggregate Stability in Carbonated and No Carbonated Soils in Tunisia

Soil Organic Carbon Fractions and Aggregate Stability in Carbonated and No Carbonated Soils in Tunisia

Symbiotic fungi that are essential for plant nutrient uptake investigated with NMP

The nuclear microprobe (NMP) technique using PIXE for elemental analysis and STIM on/off axis for parallel mass density normalization has proven successful to investigate possible interactions between minerals and ectomycorrhizal (EM) mycelia that form symbiotic associations with forest trees. The ability for the EM to make elements biologically available from minerals and soil were compared in field studies and in laboratory experiments, and molecular analysis (PCR-RFLP) was used to identify ectomycorrhizal species from the field samplings. EM rhizomorphs associated with apatite in laboratory systems and in mesh bags incubated in forest ecosystems contained larger amounts of Ca than similar rhizomorphs connected to acid-washed sand. EM mycelium produced in mesh bags had a capacity to mobilize P from apatite-amended sand and a high concentration of K in some rhizomorphs suggests that these fungi are good accumulators of K and may have a significant role in transporting K to trees. Spores formed by arbuscular mycorrhizal (AM) fungi in laboratory cultures were compared with spores formed in saline soils in Tunisia in Northern Africa. We found lower concentrations of P and higher concentrations of Cl in the spores collected from the field than in the spores collected from laboratory cultures. For the case of laboratory cultures, the distribution of e.g. P and K was found to be clearly correlated.

Nitrogen-fixing sinorhizobia with Medicago laciniata constitute a novel biovar (bv. medicaginis) of S. meliloti

Sixty-eight new rhizobial isolates were obtained from root-nodules of Medicago laciniata and from Mediterranean soils in Tunisia and France. All of them were identified as Sinorhizobium meliloti on the basis of PCR-RFLP analyses of 16S rDNA and the intergenic spacer sequence between 16S and 23S rDNAs. DNA/DNA hybridization, phenotypic characterization and 16S rRNA gene sequencing led to the conclusion that they belong the same taxon. All new isolates shared the ability to nodulate and fix nitrogen with M. laciniata except 11 of them not capable of fixing nitrogen with this plant and originating from French soils containing no efficiently adapted symbionts with M. laciniata. The nitrogen-fixing rhizobia on M. laciniata differed markedly from the other S. meliloti or Sinorhizobium medicae isolates and references in their symbiotic traits such as nifDK RFLP diversity, nodA sequences and nitrogen effectiveness with tree other different annual Medicago species ( M. truncatula, M. polymorpha and M. sauvagei). Two infrasubspecific (biovar) divisions are therefore proposed within S. meliloti: bv. medicaginis for Sinorhizobium efficient on M. laciniata and bv. meliloti for the classically known S. meliloti group represented by the strains ATCC9930 T and RCR 2011 efficient on M. sativa.

Agrophysical assessment of black shrinking soils of Tunisia

A new approach for assessment of soil physical conditions is based on forecasts of the soil water and air regimes. This approach uses the water retention curve and unsaturated conductivity of each soil layer to calculate soil regimes and estimate the possibilities of occurrence of periods of water and air deficit under standard boundary conditions. This approach has the advantages that it assesses these regimes, which govern crop yield, and considers properties of whole soil profiles. These advantages are manifested in the assessment of black shrinking soils.

Geochemical determination of the gypsum requirement of cultivated sodic soils. I. Development of the thermodynamic model GYPSOL simulating the irrigation water‐soil chemical interactions

Abstract A thermodynamic model, GYPSOL, which simulates the water‐soil chemical interactions, is presented. This model is aimed at the assessment of the gypsum requirement of sodic soils. It considers only the major chemical species and searches for the soil solution‐minerals‐adsorbing complex equilibrium through the minimization of Gibbs free enthalpy, which affords fast calculations. The model was tested on two sets of experimental data obtained from sodic waters and soils in Tunisia.

Utilization of treated wastewaters and sewage sludge in agriculture in Tunisia

Treated wastewaters (600 mm) and sewage sludge (30 T D.M./ha) supplied during two years on a sandy soil in Tunisia resulted in important changes of the soil chemical composition. An increase of the salt, fertilizing (N, P, K) and trace elements (Cu, Pb, Zn) content has been noticed. The combined application of treated wastewaters and sewage sludge does not constitute, in the short term, a polluting load.