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Nāri-calcrete is a calcareous formation common in the semiarid Mediterranean region of the Levant. The profile studied in Nazareth (Galilee) is 2.75 m thick and divided into the four conventional layers, i.e. a chalky bedrock, a powdery lower nāri, an indurated and platy upper nāri, and a laminar crust capping the profile. In this study, mercury intrusion porosimetry (MIP) is used to assess the genetic processes at work in the formation of nāri-calcrete. Based on the former work by Yaalon and Singer (1974) and MIP results, various parameters are proposed to describe the different layers: total porosity (N P ), trapped porosity (N T ), permeability (K), and strength (σ c ). These parameters are compared to each other for each layer, as well as with their respective calcium carbonate contents. An unexpected relationship shows that the more CaCO 3 is present, the more porous the layer of the nāri. Consequently, the lower nāri is interpreted as a weathering layer of the parent chalk, whereas the upper nāri, which is the most porous and the richest in CaCO 3 , results from in situ recrystallization. The upper nāri permeability precludes it from playing the role of a “plugged horizon” to explain the formation of the laminar crust. In conclusion, the nāri-calcrete in Nazareth questions the conventional model of calcrete genesis as its cementation is due to in situ redistribution of CaCO 3 rather than its translocation. These results strengthen Yaalon and Singer (1974)'s conclusions. [ABSTRACT FROM AUTHOR]

The abundant and diverse calcareous nannofossil assemblages found in the sediments of two ODP cores from the Western (Site 975B, South Balearic Basin) and Eastern (Site 969B, Mediterranean Ridge) Mediterranean Sea have been taken into account for the paleoenvironmental reconstruction of the surface water conditions during the first 490 kyrs immediately following the end of the Messinian Salinity Crisis, chronostratigraphically settled at 5.332 Ma. The areal distribution of the calcareous nannofossils is closely linked to their ecological and environmental affinities, mostly driven by temperature, salinity, nutrients or other chemical parameters of the water masses. Hence, taxa (or groups of taxa) showing well-known ecological behaviors were considered, and different environmental evolutions were recognized for the two sectors of the Mediterranean Basin during the early Zanclean (early Pliocene). Specifically, in the Western Mediterranean a switching from a warm and oligotrophic water environment, showing normal open-marine conditions, to a colder and eutrophic one, characterized by a decrease in salinity rates and the development of a more restricted environment, can be recorded. Conversely, in the Eastern Mediterranean the environmental setting immediately following the MSC is indicative of temperate waters and normal open-marine conditions, which evolves, in the younger layers, to a warmer environment characterized by high salinity rates and typical of a restricted marine context. The timing of the environmental transitions recognized at the two sites has been set through the Principal Component Analysis. Taxa and groups of taxa reflecting precise ecological affinities have been handled together and a transition interval have been defined between 5.20/5.15 Ma and 5.06/4.98 Ma, and between 5.10 Ma and 4.92 Ma in the Western and Eastern Mediterranean, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A set of periurban calcareous agricultural Mediterranean soils, with a natural gradient in the content and composition of organic matter (OM), was spiked with a mixture of Cd, Cu, Pb and Zn at two levels – designated Tt1 and Tt2 – within the limit values proposed by the current European legislation and incubated for ≤12months. We conducted bioassay experiments with romaine and iceberg varieties of lettuce (Lactuca sativa L.). Metal bioavailability patterns were evaluated as a function of soil constituents and extractable metals. Metal contamination produced a decrease in plant biomass (up to 50%) and nutrient imbalance. The redundancy analysis showed that the carbonate, OM and fine mineral fractions account for up to 85% of the variance in metal bioavailability patterns in lettuce plants. Carbonate and fine mineral fractions were negatively related to Cd and Zn bioavailability in plants respectively. Organic matter explained Cu and Pb bioavailability, although patterns varied between plant tissues according to their organic composition. The labile fraction limited metal absorption of Pb by roots at the Tt2 level and Cu at both levels, but Cu and Pb translocation was enhanced at both levels. There were significant correlations between metals in leaves and metals extracted with both neutral salts and complexing agents. The high rate of metal translocation and the considerable influence of soil properties may indicate that the limiting values of metals in soils proposed by the current European legislation should be revised in the case of multi-component systems, and/or be established according to the soil characteristics. [Copyright &y& Elsevier]

Abstract: The involvement of the bacterial community of an agricultural Mediterranean calcareous soil in relation to several heavy metals has been studied in microcosms under controlled laboratory conditions. Soil samples were artificially polluted with Cr(VI), Cd(II) and Pb(II) at concentrations ranging from 0.1 to 5000mgkg−1 and incubated along 28d. The lowest concentrations with significant effects in soil respirometry were 10mgkg−1 Cr and 1000mgkg−1 Cd and Pb. However, only treatments showing more than 40% inhibition of respirometric activity led to significant changes in bacterial composition, as indicated by PCR–DGGE analyses. Presumable Cr- and Cd-resistant bacteria were detected in polluted microcosms, but development of the microbiota was severely impaired at the highest amendments of both metals. Results also showed that bioavailability is an important factor determining the impact of the heavy metals assayed, and even an inverted potential toxicity ranking could be achieved if their soluble fraction is considered instead of the total concentration. Moreover, multiresistant bacteria were isolated from Cr-polluted soil microcosms, some of them showing the capacity to reduce Cr(VI) concentrations between 26% and 84% of the initial value. Potentially useful strains for bioremediation were related to Arthrobacter crystallopoietes, Stenotrophomonas maltophilia and several species of Bacillus. [Copyright &y& Elsevier]

The Mediterranean climate allows for rainfed cropping in the relatively moist cool period from autumn to late spring/early summer. Drought has a constant influence. Soil fertility was partly maintained by fallowing, nitrogen-fixing plants, and animal manures. Considerable changes have occurred due to land use pressure, i.e. decreasing fallow and increasing crop diversification, irrigation, and chemical inputs, especially chemical fertilizers. Generally, N use has increased about 20-fold, while phosphate has also increased significantly. Due to adequate reserves in the soils, there is a limited potassium fertilizer use. Awareness of the significance of micronutrients has developed. This presentation gives a broad overview of nutrients in relation to soil properties and crops, emphasizing nutrient dynamics in agroecosystems and nutrient use efficiency. Chemical fertilizers have contributed significantly to increasing crop output in the Mediterranean region. Fertilizers and nutrients are considered in the broadest sense, i.e. agricultural production, human and animal health, and the environment. Attention is given to the potential contribution of soil and cropping systems to the emission of greenhouse gasses and how soil management is likely to need to respond to the likelihood of climate change. Projections about future changes related to soil resources of the Mediterranean region are seen in the light of global trends. [ABSTRACT FROM AUTHOR]

Abstract: Lithogenic and/or secondary carbonates are present in many semi-arid Mediterranean soils. Their role in aggregation dynamics is not completely known, and can determine the sensitivity of these soils to land-use changes and soil management. The objective of this work was to test the hierarchical model of aggregation, and to determine the relationship between aggregates formation and organic matter decomposition in calcareous soils of semi-arid Mediterranean regions, by comparing macroaggregation in the upper horizon of a calcareous soil (Typic Calcixerept) with a non-calcareous soil (Typic Haploxerept) and a decarbonated terra rosa (Calcic Haploxerept) following fresh straw addition under controlled laboratory conditions during 105days. We hypothesized that aggregation would work according to the hierarchical model in the non-calcareous soil (NONCALC) and in the decarbonated terra rosa (DECALC), but not in the calcareous soil (CALC). The three soils had similar organic C concentrations and C/N ratio, but differed in their carbonates and clay minerals content: NONCALC had a similar proportion of clay-size silicates than CALC (~10%), and the DECALC had a similar proportion of total clay-sized particles than CALC (including carbonates, ~20%). An increase in the amount of macroaggregates (>250μm) and microaggregates (50–250μm) held within macroaggregates associated to an increase in the fungal activity when maize straw was added, a decline of macroaggregates with time associated to organic matter decomposition, a higher concentration of organic C and maize-derived C in microaggregates within macroaggregates than in free microaggregates, and a transfer of maize-derived C from macroaggregates to free microaggregates with time confirmed that aggregation worked according to the hierarchical model in NONCALC and DECALC. In CALC, however, the hierarchical model worked only partially. Macroaggregates formation was also stimulated by organic residues addition according to the model, but stable macroaggregates showed longer turnover rates and no relationship between straw decomposition and their decline was observed. From this, we postulate that carbonates can help stabilizing macroaggregates formed from fresh organic matter decomposition through abiotic processes, such as dissolution and re-precipitation. These results help to understand field data obtained in semi-arid calcareous agricultural soils, where it has been observed that aggregation is not always directly correlated to organic matter concentration, but that increases in soil organic matter can promote aggregation. They also indicate the need for considering the composition of the mineral fraction when modelling soil structure in semi-arid Mediterranean soils. [Copyright &y& Elsevier]

Abstract: This study determines extractable levels of Cd, Cu, Pb, Zn, Ni and Co in western Almería (Spain) greenhouse surface soil horizons using EDTA solution, which is identified as the fraction available for organisms and plants. It also establishes background levels, geochemical baseline concentration and reference values (RV), and investigates the possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these extractable heavy metals was high as those reported by other authors for Spanish agricultural soils. The available RV concentrations obtained (mgkg−1) were: Cd 0.17, Cu 1.6, Pb 13.8, Zn 5.0 Ni 1.7 and Co 2.9. Using the upper baseline criterion, 95% of greenhouse soils present a relatively higher content of extractable heavy metals given their Cd and Cu concentration. Significant correlations between total and EDTA-extractable metal levels were found for Zn, Pb, Cu, Cd and Ni. Soil properties also related to heavy metals content, suggesting that Cd, Cu, Pb and Zn are of similar origin and relate to anthropic activities, and implies the same interactions and/or relationships among these metals. [Copyright &y& Elsevier]

Abstract: This paper provides the first available information on the determination of the total mercury content in different Mediterranean calcareous soils by thermal decomposition, amalgamation and atomic absorption spectrophotometry. Fifty-three samples from five soil use groups (natural, dry land, greenhouse, irrigated and rice farming soils) were analysed. The results show that the levels of mercury in these soils were 9.4–1585μgkg−1. Soil organic matter and the zinc equivalent index have been related to Hg content in soils, suggesting that Cu, Ni, Zn and Hg are of a similar origin. The background level (BL), geochemical baseline concentrations (GBC) and the reference value (RV) were established from natural soils. Calculations are according to the log-normal distribution criterion. The BL, GBC and RV values obtained were 25.1, 9.8–64.3, and 64.3μgkg−1, respectively. The BL was similar to the baseline concentration in soils obtained at Admiralty Bay (Antarctica) (24.6μgkg−1) and a Spanish peat bog (Galicia) (22μgkg−1). These data show that rice farming soils (gleyic–calcaric Fluvisols, Fluvaquents), irrigated soils (calcaric Fluvisols, Xerofluvents) and some greenhouse soils (cumulic Antrosols) presented much higher levels, indicating contamination. Hg accumulation in these soils was associated with local anthropogenic sources. [Copyright &y& Elsevier]

Phosphorus (P) deficiency and low P-use efficiency are induced by soil properties, especially in calcareous soils, which are dominant in semi-arid regions of the world such as the Mediterranean region. Alternative approaches to P fertilization involve exploiting plant genetics in order to achieve more efficient use of P by the growing crop. Accordingly, in a greenhouse pot experiment, we evaluated P-efficiency in wheat genotypes grown in typical calcareous soils in southern Turkey. Ten common local genotypes were grown in six soil series for eight weeks using five P application rates (0, 25, 50, 100, and 200 mg P kg-1). Dry matter (DM) yield and P content were significantly increased by increasing P rates, with significant differences between soils. Some genotypes performed better under P stress because of better P utilization efficiency. Shoot DM was the most sensitive indicator of genetic variability under P-deficient conditions. Genotypes classified as efficient-responsive (Adana-99, 1014, Golia, Balatilla) had above average DM yield when P was not added, and responded well to P applications; efficient-non-responsive genotypes (Firat-93, Seri-82, Genc-99, Panda) had below average DM yield, but responded to P applications; inefficient-non-responsive genotypes (Fuat Bey and Ceyhan-99) had below average DM yield; and no genotypes were in the inefficient responsive category. Such P response categorization is needed for better breeding programs for nutrient-use efficiency. The study may aid in selecting P-efficient genotypes in low-P soils, especially where little P is used. The use of P-efficient genotypes should be seen as complement to, rather than a substitute for, chemical P fertilization depending on local conditions. [ABSTRACT FROM AUTHOR]

Abstract: The effect of changes in land use on the early stages of soil water erosion was studied on brown calcareous soils (Calcic Luvisols), a widespread type of soil suitable for wine-growing in the French Mediterranean area. This type of soil is subject to high intensity rainfall events. Rainfall of 60mm/h was simulated on dry soil for several types of land use including scrubland, fallow and several wine-growing strategies (chemical and mechanical inter-row weeding, grassing, straw mulching, rock fragment cover and clearing rock fragments). No soil loss was observed for fallow and scrubland. The highest runoff rates and soil losses were observed for chemically weeded vineyards, with however, a reduction of soil losses when the prunings were left on the soil. Vineyards mulched with straw or with rock fragment cover were protected against runoff and soil erosion. As the grassing was recent, it was only partially effective, although several indicators showed that it might be promising in the future. A method of ranking the land uses in terms of protection against runoff and soil losses was derived from the experimental data. The statistical relationships between runoff, soil losses and various surface properties (soil cover including litter, weeds and rock fragments, crusts) and properties of the 0–5cm topsoil layer (aggregate stability, carbon organic content, and porosity) were determined. The rate of initial crusts, the crusting with the rains, the aggregate stability, the carbon organic content and the soil porosity were significantly related to the runoff. The soil cover and the crusting with the rains were significantly related with the water turbidity. All theses parameters were significantly related to soil losses. However, runoff was poorly related to the water turbidity. The causality links between the results and the ranking of the land uses are discussed. [Copyright &y& Elsevier]

Abstract: Many soils in the semiarid Mediterranean Ebro Valley of Spain are prone to physical and chemical degradation due to their silty texture, low organic matter content, and presence of carbonates, gypsum or other soluble salts. Rainfed agriculture on these soils is also hindered by the scarcity of water. No-tillage can increase plant-available water and soil organic matter, thus helping overcome most factors limiting crop production in this area. Our objective was to determine how conventional- and no-tillage practices affected soil physical quality indicators and water availability in an on-farm study in the Ebro Valley. Soil samples were collected from 0 to 5-, 5 to 15-, and 15 to 30-cm depth increments within adjacent farmer-managed conventional- and no-tillage fields in 2007 and 2008. Both fields were managed for continuous barley (Hordeum vulgare L.) production. The soil at both sites is a silt loam (Haplic Calcisol). Aggregate-size distribution and stability, soil water retention characteristics, organic carbon, and total carbonates were determined in 2007. Pore-size distribution was estimated from the water retention curve. Penetration resistance, soil bulk density and field water content during the entire crop growing season were measured for both fields in 2008. Aggregate dry mean weight diameter and stability in water were 1.2 and 2.2 times greater, respectively, under no-tillage than conventional tillage due to reduced mechanical disturbance and increased soil organic carbon content. Bulk density was 1.12 times greater (P <0.1) under no-tillage only in the 0–5-cm depth. Two times greater penetration resistance to a depth of 15cm in this treatment was related to bulk density and aggregates stability. Field water content was greater with no-tillage than conventional tillage during the driest months in 2008. The volume of equivalent diameter pores (0.2–9μm) was 1.5 times higher under no-tillage. This increased plant-available water content and doubled barley production under no-tillage in 2008, which was a very dry year. We conclude that despite the greater penetration resistance under no-tillage, increased water availability as a result of improved structure characteristics was more important for crop yield. This suggests that producers should seriously consider adopting no-tillage practices for soil conservation in semiarid degraded areas like the one studied. [Copyright &y& Elsevier]

In the Mediterranean region, much emphasis is placed on the role of fertilizers in enhancing crop production to achieve food security. Given the complex nature of phosphorus (P) reactions in soils, considerable research has dealt with fertilizer aspects related to efficient P use, but comparatively less emphasis has been given to plant variation with respect to P efficiency. In this study, selection and adaptation of P-efficient corn genotypes was seen as one possible approach to enhancing P efficiency. Thus, a greenhouse experiment with 10 corn genotypes (traditional to modern), five P application rates (0-200 mg kg-1), and four field trials with three genotypes for 2 years were carried out on various calcareous soils (Vertic Torrifluvent, Vertic Calciorthid, Entic Chromoxerert, and Typic Xerofluvent). Measurements were made of root characteristics. Treatments in the field trials were five P application rates as main plots (0-68 P ha-1) and three corn genotypes as subplots. Genotypes were selected for the field trials from the greenhouse experiment as “efficient-responsive,” “efficient-nonresponsive,” and “inefficient-responsive.” Dry-matter (DM) yield and plant P uptake by plants increased with P application rates in the greenhouse experiment. Root length and mass were considerably increased by increasing P levels. Genotypes were classified for P efficiency. The studies indicated that because corn genotypes respond to P-fertilizer application differently, this trait could be utilized to exploit native and applied P more efficiently, especially at low levels of available P and when P- fertilizer use is limited. This differential response derives from morphological, physiological, and genetic variability among the genotypes. Although genotypic efficiency is important for fertilizer management, the contribution of the efficiency is not a substitute for fertilizers, especially if high yields are required. Nevertheless, breeding for P-use efficiency should be a component of any program to improve crop yield potential. [ABSTRACT FROM AUTHOR]

Citrus crops in the Mediterranean region are often grown in high pH calcareous soils, which promote nutrient imbalances, especially iron deficiency. 'Navelina' trees grafted on eight different citrus rootstocks were assessed in terms of their relative tolerance to these soils. To do so, leaf gas exchange and chlorophyll a fluorescence parameters were measured for 2 consecutive years in leaves without visible injury symptoms. Trees were grown on the rootstocks Carrizo citrange, hybrids of Cleopatra mandarin x Poncirus trifoliata no. 5 (F-A 5), 13 (F-A 13), and 16 (030116), Troyer citrange x common mandarin no. 18 (F-A 418), King mandarin x P. trifoliata no. 7 (F-A 517), 020324 (Troyer citrange x Cleopatra mandarin), and Volkamer lemon x P. trifoliata no. 64 (230164). gS and transpiration rate were clearly lower in leaves of shoots grafted on Carrizo citrange than in those on the other rootstocks assayed, but net photosynthetic flux did not differ. However, leaves of shoots on Carrizo citrange displayed a decline in their maximum quantum yield of PSII photochemistry [variable fluorescence/maximum fluorescence (Fv/Fm) ratio] and other chlorophyll parameters in the steady state such as photochemical quenching (qP) and the quantum efficiency of PSII photochemistry (ΦPSII) as well as an increase in nonphotochemical quenching (qN). Other rootstocks such as 030116, F-A 517 and, especially, F-A 5 showed the highest ΦPSII and Fv/Fm values, whereas F-A 5 had the lowest qN in the steady state. The photosynthetic characteristics observed in leaves on Carrizo citrange showed them to be the least tolerant to these calcareous conditions, whereas photosynthesis of 'Navelina' trees budded on F-A 5 were the most tolerant. [ABSTRACT FROM AUTHOR]

Abstract: Petrocalcic horizons are frequent in soils of semiarid landscapes. A survey of SIC and SOC contents made in Southern Spain in a pilot area with well defined geomorphological surfaces showed that topsoils overlying petrocalcic horizons are almost twice as rich in SOC as soil of similar depth without petrocalcic horizons. This could be due to impedance to root penetration, changes in redox potential and soil water availability caused by the presence of indurated crust. Soil age, on the contrary, seems not be an essential factor, since only a short time is required to reach a steady state in SOC in comparison to the time span available for soil formation on the different geomorphic surfaces. [Copyright &y& Elsevier]

Water repellency (WR) is a property affected by fire and of crucial importance in the hydrological behaviour of soils after burning. In dry Mediterranean areas knowledge of the factors that control the development of water repellency by fire is of particular interest. We examined such factors in two calcareous soils, a Regosol and a Luvisol, representative of forest areas of southeast Spain. Heating temperature (200–500°C), vegetation type ( Rosmarinus officinalis, Pinus halepensis and Brachypodium retusum), quantity of vegetation litter (control, low and high) and type of soil were selected as factors for assessing the WR induced by fire. The two soils exhibited markedly different WR responses after heating, the Regosol being much more susceptible than the Luvisol. Characteristics such as organic matter and clay content seem to determine the different WR responses to heating. We found that the type and quantity of vegetation litter also control the persistence of induced WR. In general, the order of increasing WR was Brachypodium < Pinus < Rosmarinus, and larger amounts of litter induced more WR. Maximum values of WR, most of them classified as severe (901−3600 s), were found in the range of 300−350°C, whereas beyond this temperature WR was destroyed. These results show that water repellency induced by combustion could be limited by environmental factors such as vegetation type and availability of litter, and that soil type and its characteristics also play a decisive role. [ABSTRACT FROM AUTHOR]