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Studies on the quantities and distribution of soil organic carbon stocks (SOC-S) can help to fill the knowledge gaps in estimating the amount of carbon stored in soils. However, one of the problems of soil organic carbon (SOC) is the high variability in space and time. Over the years, many researchers have studied the soil mainly in two different ways: by pedogenic horizons in entire soil profiles (ESP) or by soil control sections (SCS) with different thicknesses along the profile, and this causes uncertainty in SOC and SOC-S evaluation and assessment. This study analyzed the differences in the SOC-S in northeastern Sardinia (Italy) in Cambisols, following two soil sampling approaches, ESP by pedogenic horizons and SCS (25 cm thick) on these selected land uses: tilled vineyards, no-till grassed vineyards, and former vineyards naturally re-vegetated after abandonment. Average data on total SOC-S (T-SOC-S) estimations were 61.5 Mg ha− 1 and 67.3 Mg ha− 1 for ESP and SCS respectively, indicating significantly higher estimates of T-SOC-S when sampling by SCS. Consequently, the ESP approach is recommended to evaluate and certify SOC-S, while SCS may be preferred for monitoring and soil management interpretation purposes.

In Mediterranean areas, conventional tillage increases soil organic matter losses, reduces soil quality, and contributes to climate change due to increased CO2 emissions. CO2 sequestration rates in soil may be enhanced by appropriate agricultural soil management and increasing soil organic matter content. This study analyzes the stratification ratio (SR) index of soil organic carbon (SOC), nitrogen (N) and C:N ratio under different management practices in an olive grove (OG) in Mediterranean areas (Andalusia, southern Spain). Management practices considered in this study are conventional tillage (CT) and no tillage (NT). In the first case, CT treatments included addition of alperujo (A) and olive leaves (L). A control plot with no addition of olive mill waste was considered (CP). In the second case, NT treatments included addition of chipped pruned branches (NT1) and chipped pruned branches and weeds (NT2). The SRs of SOC increased with depth for all treatments. The SR of SOC was always higher in NT compared to CT treatments, with the highest SR of SOC observed under NT2. The SR of N increased with depth in all cases, ranging between 0.89 (L-SR1) and 39.11 (L-SR3 and L-SR4).The SR of C:N ratio was characterized by low values, ranging from 0.08 (L-SR3) to 1.58 (NT1-SR2) and generally showing higher values in SR1 and SR2 compared to those obtained in SR3 and SR4. This study has evaluated several limitations to the SR index such as the fact that it is descriptive but does not analyze the behavior of the variable over time. In addition, basing the assessment of soil quality on a single variable could lead to an oversimplification of the assessment. Some of these limitations were experienced in the assessment of L, where SR1 of SOC was the lowest of the studied soils. In this case, the higher content in the second depth interval compared to the first was caused by the intrinsic characteristics of this soil's formation process rather than by degradation. Despite the limitations obtained SRs demonstrate that NT with the addition of organic material improves soil quality.

Carbon sequestration in agricultural soils has been defined as a positive strategy in the mitigation of global warming. The selection of the appropriate soil management system to achieve this goal is fundamental. In this study the effect of two tillage treatments, conventional tillage (CT) and no tillage with bare soil (NT) was analyzed in the complete soil profile (by horizons) in a rainfed olive grove under Mediterranean conditions. The objective was to determine the influence of treatments on soil aggregation and organic carbon (OC) distribution within aggregate fractions both in the surface horizon (0–32.7 cm in CT and 0–21 cm in NT) and in depth (32.7–119.7 cm in CT and 21.7–110 cm in NT) (Bw, BC and C horizons). Soil samples from all horizons were separated into four aggregate-size fractions: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and silt + clay (

Understanding soil dynamics is essential for making appropriate land management decisions, as soils can affect the carbon content from the atmosphere, emitting large quantities of CO 2 or storing carbon. This property is essential for climate change mitigation strategies as agriculture and forestry soil management can affect the carbon cycle. The Mediterranean dehesa (Mediterranean grassland ecosystem with scattered oak trees — grazing system with Quercus ilex spp. ballota ) is a silvopastoral system that integrates forestry, agricultural and livestock practices. The dehesa is characterized by the preservation of forest oaks that provide environmental services including carbon capture and storage. This paper shows the relationships between soil properties and soil organic carbon (SOC) in two soil types: Cambisols (CM) and Leptosols (LP), with two management systems: organic farming (OF) for 20 years and conventional tillage (CT) in a Mediterranean dehesa of southern Spain without cropping. An analysis of 85 soil profiles was performed in 2009 in Los Pedroches Valley (Cordoba, southern Spain). The SOC stock (SOC-S) was greater in CM (75.64 Mg ha − 1 ) than in LP (44.01 Mg ha − 1 ). Physical parameters were the main variables affecting soil development. SOC-S was very similar in OF and CT (CM [74.90 Mg ha − 1 -CT; 76.39 Mg ha − 1 -OF] and LP [44.77 Mg ha − 1 -CT; 43.25 Mg ha − 1 -OF]). Data analysis showed that management practices had little effect on SOC storage in the study zone. Significant differences between soil types and management practices were found in SOC content for different horizons. The stratification ratio was > 2 in both soils types (CM and LP) and management systems (OF and CT). These results indicate that the soil is of high quality, and that management practices have little influence on SOC-S in Los Pedroches Valley.

The purpose of this paper is to outline a procedure for soil block extraction, which is highly appropriate for clay soils. The method described here is rapid and cheap and has been used successfully by us in clay soils in southern Spain for the last six years. A wooden box is used to shape the soil block in situ and protect it during its transport from the field to the laboratory. Polyurethane foam was selected as the bonding agent, between the wooden framework and the soil block in order to avoid any possible alterations of the soil. This type of foam is used because it is strong, durable and non-toxic. The polyurethane foam is applied to the soil block as a permanent coating. This technique allows us to extract the clay soil solution in the laboratory.

In Spain, agriculture triggers soil degradation and erosion processes. New strategies have to be developed to reduce soil losses and recover or maintain soil functionality in order to achieve a sustainable agriculture. This experiment was designed to evaluate the effect of two olive mill wastes (olive leaves and “alperujo”) on soil properties and soil erosion in a rain fed olive grove in SE Spain. After three years experiment, oil mill wastes application significantly improved physical and chemical properties of the studied soil with respect to control. The organic matter content, bulk density and porosity were increased, which confirmed the interactions of these properties. Available water capacity increased with olive leaves but decreased when applied “alperujo”. With respect to erosion, after simulated rainfall experiments it was found that the oil mill wastes contributed to increase the roughness and the interception of raindrops, delaying runoff generation and enhancing the infiltration of rainwater. Treatment with oil mill wastes contributed to a reduction in runoff generation and soil losses compared to bare soil, especially when applied olive leaves.

Potassium is an essential macronutrient for plants; it is characterized by increased photosynthetic activity by ensuring a better utilization of light energy, also acts as a regulator of cell osmotic pressure, decreasing transpiration and helping to maintain cell turgidity. However, the sodium is not an essential element for plants, although it is beneficial to certain crops, in some instances can replace the potassium and osmotic regulation making and turgidity of the cells, this effect is greatest when the supply of potassium is deficient ( Wild, 1992 ). Both elements, in periods of aridity, delayed the wilting of plants to maintain cellular osmotic potential and in cold periods, they lower the freezing point of sap ( Navarro and Navarro, 2000 ). This is an experiment to study the influence of soil management techniques on the monovalent cations in soil solutions at different depths. The cropping systems studied are conventional tillage, minimum tillage and direct drilling. Conventional tillage releases more Na + and K + to the soil solution than the conservative techniques. In the case of Na + , the conventional tillage soil solution has an average concentration of 0.563 meq/L compared to 0.303 meq/L of minimum tillage and 0.340 meq/L of direct drilling. As for the K + , the soil solution concentration of conventional tillage is 0.097 meq/L, compared to 0.079 meq/L of the solution of minimum tillage and 0.056 meq/L of direct drilling. The behavior for the two cations studied is distinct at different depths. The Na + is more abundant in water samples of soil taken in depth. Therefore, the salinization risk may take place in the subsoil, especially in conventional tillage where the Bw 1 horizon values are three times higher than in the Ap horizon, while the K + is more abundant in the surface horizon. Conventional tillage and minimum tillage techniques, in the Ap horizon have a similar pattern with a K + concentration average of 0.15 meq/L and 0.14 meq/L, respectively, resulting in lower values for direct drilling. Studies on clay soils have not been performed previously because of the difficulty presented by these soils when soil solution extracted for analysis. We analyzed the monovalent cations (sodium and potassium) from soil solution; because the soil solution is the immediate source of sodium and potassium for plants.