Sub-chapter 3.5.2. Soils and desertification in the Mediterranean region

Chemical Characteristics of Two-Phase Olive-Mill Waste and Evaluation of Their Direct Soil Application in Humid Mediterranean Regions

“…In the Mediterranean zone, soils are usually much shallower than in the humid tropics and in the temperate zone, where pedogenesis is faster and erosion less ancient. Shallow soils with low nutrients and water storage capacity are a major constraint to natural vegetation and crop cover, which in turn affords weak protection to soils from water and wind erosion [7]. Also, for organic farming systems, the application of two-phase OMW to soil represents an interesting option that also 'closes' the cycle of residue resources [4].…”

Assessing the Long-Term Impact of Traditional Agriculture and the Mid-Term Impact of Intensification in Face of Local Climatic Changes

“…As usually practiced today, agricultural intensification has a double-link effect across the ecosystem, with soils losing their richest layer to the sea through accelerated erosion created by anthropogenic weathering, such as tillage, plowing, harrowing or scarification [1], primary causes responsible for the continuous decline in soil organic matter (SOM) levels and edaphic compaction [2][3][4][5]. Also, there is also an increased salinity in soils due the higher amounts of fertilizers in irrigation water [6][7][8].…”

“…Salt accumulation leads, above all, to low agricultural production, soil erosion, decreased permeability and infiltration rate of the soil, low groundwater recharge, compacting, crusting and invariably to low economic returns [9]. The degradation of the Mediterranean basin soils [10,11] is but a particular example of the ecosystem unsustainability with ever growing desertification hotspots due to the global and local climate change and inadequate local practices with the soils becoming more alkaline, saline, and deprived of SOM [1,4,[12][13][14] exposing the importance of adopting a multidimensional approach for agricultural sustainability in the Mediterranean basin, as demonstrated in the studies of Stagnari et al [15], Pagnani et al [16] and Farooq et al [17]. The growing problem of saline and sodic soils already affects a quarter of all agricultural soils degrading the soil structure by means of clay swelling and dispersion and is more present in areas experiencing desertification whether they are arid or semi-arid [18][19][20].…”

“…Calcium, magnesium, sodium and potassium tend to accumulate in semi-arid and arid regions as the amount of precipitation in the basin is not sufficient to leach the chlorides and sulfates salts even when these soils are under irrigation [24] and, thus, the primary and secondary salinity in the Mediterranean basin seems to be unavoidable with this condition only worsening due to the general thin layers, poorer drainage capacity of these soils and dry climate [1,25]. Where the precipitation, or precipitation plus irrigation water, is less than the potential evapotranspiration (ET0) the cations released, be it by mineral weathering or anthropically added [6], accumulate as there is not enough precipitation to thoroughly leach them away leading to the alkalinization of the soils depending on the equilibrium between the acid (H + , Al 3+ ) and non-acid cations (Ca 2+ , Mg 2+ , K + and Na + ) in the soil colloids and the equilibrium between H + and OHin the soil solution, both controlled by the nature of the soil colloids.…”

“…Because the deflocculating monovalent ions Na + and K + are not leached from the soils of the dry regions, the type of clays dominating in alkaline soils tend to deflocculate or disperse which furthers the reduced macroporosity, aeration, water percolation and sealing of the soil surface. In our opinion, the edaphic impact of these ions is well described in the 'cation ratio of soil structural stability' (CROSS) equation (Equation (1)) as it considers the different effects of Na + and K + in deflocculating, and that of Mg 2+ and Ca 2+ in flocculating, soil clays that parameterize the structural effects in the soil solution better than the Sodium Adsorption Ratio (SAR) or the Potassium Adsorption Ratio (PAR) as demonstrated by Rengasamy and Marchuk [26] and that is being adopted by the scientific community for the last decade [27][28][29][30].…”