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Land use change from natural vegetation to agricultural land often affects the properties and quality of soils. A field study was conducted to determine the effects of land use change [Mediterranean evergreen oak woodland (MEOW-dehesa) to olive grove and cereal] on soil organic carbon (SOC) and nitrogen (N) concentrations and stocks, and on the soil quality in Cambisols in The Cardena-Montoro Nature Reserve (South Spain). The land use change from MEOW-dehesa to olive groves increased the SOC concentration (MEOW-dehesa: 19.4 g kg−1; 7.2 g kg−1; olive grove: 41.8 g kg−1; 15.4 g kg−1 in the surface and subsurface layers respectively) and stock (22.3% higher in olive grove than in MEOW-dehesa and 17% higher in olive grove than in cereal), but did not affect the N concentration and decreased N stock in the surface layer. The conversion from MEOW-dehesa to cereal did not affect SOC stock and concentration; it only decreased the N concentration and stock in the surface layer (N: 1.6 g kg−1 and 1.1 g kg−1 in MEOW-dehesa and cereal respectively; N stock 4.2 Mg ha−1 and 2.9 Mg ha−1 in MEOW-dehesa and cereal respectively). After the land use change to olive grove stratification ratios increased, however in cereal they decreased. Comparing the different types of MEOW-dehesa, significant differences were found. It is important to point out that all the stratification ratios calculated were >2.

In Mediterranean areas, through the years, natural forest (NF) areas have suffered land use change (LUC) mainly for economic reasons. This is the case of olive groves (OG) in Andalusia (south Spain), the main olive oil production area in the world. This LUC from NF to OG has caused soil erosion and the loss of soil quality. Also, this effect has been aggravated by climatic conditions and poor soil management practices. A field study was conducted to examine the effects of LUC from NF to OG in a toposequence (summit-SM, backslope-BS and toeslope-TS) and to determine soil organic carbon (SOC), nitrogen (N) and the stratification ratio (SR) of SOC in the Torredelcampo–Jaen–Spain (Mediterranean area) in a Calcisols–Regosols–Vertisols sequence. Total SOC (T-SOC) was low for both NF and OG soils. In the case of NF, there was a pattern of decrease from the highest (SM) to the lowest topographical position (TS); whereas for OG, the highest T-SOC was found in TS (50.2 ± 1.1 g kg−1). T-SOC was more than 40% higher in NF than in OG in SM and BS. The total SOC stock (T-SOCS) in NF soils remained evenly distributed in the three topographical positions. However, the trend for the OG soils was an increase of T-SOCS along the hillside (SM: 68.9 ± 4.8 Mg ha−1; BS: 82.3 ± 12.3 Mg ha−1 and TS: 158.7 ± 15.4 Mg ha−1). N followed a pattern of decrease with depth in the OG soils, but not in NF soils. As for N stock, it was higher in NF than in OG, with the exception of NF-TS and OG-TS. SR values in NF had a general trend of increasing from higher to lower topographical positions, despite the fact that T-SOC decreased from higher to lower topographical positions. This indicates that soil quality is higher in lower topographical positions even though there is less T-SOC. SR values in OG soils had a similar trend as in NF soils (but with lower values). However, T-SOC increased as well in the same way, which was opposite to the NF soils case. Therefore, soil quality was higher in lower topographical positions for both land uses.

In Mediterranean Europe, dehesa is the most widespread agroforestry system, that integrates forestry with agricultural and livestock management practices. It is characterized by the conservation of forest oaks to provide environmental services including carbon capture and storage. During the past two decades, many dehesa areas have been converted to olive groves with little information regarding long-term effects on soil organic carbon (SOC) distribution, total nitrogen (TN) concentrations, C:N relation, or stratification ratios (SR) throughout the soil profile. Understanding carbon and nitrogen dynamics is essential for making appropriate land management decisions. Our objective was to qualify SOC, TN, and profile SRs after Eutric Cambisols were converted from dehesa to olive groves using organic or conventional management practices for approximately 20 years. We analyzed soil profile samples from 45 farms in 2009 in Southern Spain. Olive groves managed using organic practices had more SOC stock (73.58 Mg ha−1) and TN stock (7.10 Mg ha−1) than dehesa. SOC and TN decreased with depth under both land uses and managements. Overall, organic farming (OF) resulted in higher SOC and TN levels than conventional tillage (CT), but the SRs were similar for both land uses and management strategies. These results suggest that, in general, these soils do not have degradation problems. Only in SR2 (defined by Ap-A/C) of SOC and SR2 of TN, showed significant differences and soils under OF had higher quality than under CT. By contrast, the C:N stratification ratio was similar in all land uses and management.

The Mediterranean evergreen oak woodland (MEOW-dehesa) is the most widespread agroforestry system in Mediterranean Europe and integrates forestry, agricultural and livestock practices. The MEOW-dehesa is a grazing system with evergreen Quercus ilex spp. ballota . It is characterized by the conservation of forest oaks ( Quercus spp.) and provides environmental benefits such as carbon capture and storage in soils. The effect of conventional tillage (CT) and organic tillage (OT) on the distribution of soil organic carbon (SOC), total nitrogen (TN) and C:N ratios has not been well documented in the MEOW-dehesa. The objective of this paper is to study these parameters in the MEOW-dehesa in two soil types (Leptosols and Cambisols) and two management systems, OT for 20 years and CT. The stratification ratio (SR) of SOC, TN and C:N ratio is also evaluated. An analysis is performed on 85 soil profiles over the 2005–2009 period in southern Spain. The SR of SOC in Cambisols was greater under OT than CT, ranging from 1.25 to 1.42 and from 1.3 to 1.6 under CT and OT, respectively. The SR of TN for 0–20.9 cm, 20.9–55.5 cm and 55.5–102.1 cm depth was greater under OT than under CT. The OT also increased the stratification of the C:N ratio compared to CT.

Olive grove soils in semi-arid Mediterranean areas are very poor in organic matter and are exposed to progressive degradation processes. Therefore, additions of the olive mill by-products as organic amendments can improve soil quality and hence mitigate the negative environmental and agronomic limitations of these soils. A field study was conducted to assess the short-term effects of two oil mill by-products [olive leaves and alperujo (a two-phase olive mill waste)] and determine soil organic carbon (SOC), total nitrogen (TN), the C:N ratio, and their stratification across the soil profile, in an area under Mediterranean conditions. The experimental design consisted on three large plots each spanning a 100 m × 100 m area covered with unirrigated olive trees of the Picual variety less than 30 years old under conventional tillage (CT) in the province of Jaen (southern Spain). One of the plots (CT) was used as control plot and the other two were treated with alperujo (CTa) and olive leaves (CTol), respectively. Soil properties were assessed three years after the by-products were applied. Supplying the soil with the by-products increased C and N stocks. Thus, the SOC stock was 75.4 Mg ha−1 in CT, 91.5 Mg ha−1 in CTa and 136.3 Mg ha−1 in CTol; and the TN stock 12.1, 13.9 and 16.1 Mg ha−1 in CT, CTa and CTol, respectively. SOC, TN and the C:N ratio in the surface horizon were higher in the treated plots (viz. 18.5 g C kg−1, 1.4 g N kg−1 and 13.2:1 in CTa, and 84.1 g C kg−1, 5.7 g N kg−1 and 14.7:1 in CTol) than in the control plot (8.9 g C kg−1, 0.9 g N kg−1 and 9.8:1, respectively). In addition, application of the by-products improved soil quality (the stratification ratio, SR, for SOC was greater than 2). Oil mill by-products such as olive leaves and alperujo are thus potentially useful as soil amendments since they are effective sources of organic matter and nitrogen, improve soil quality and alleviate the environmental and agronomic limitations of Mediterranean agricultural soils, even those under using CT. In addition, the by-products can be recycled on site.