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The soil-management system in agricultural lands could be affected substantially on dynamics of CO2 fluxes from soil. An experiment was carried out in Lanjaron (SE Spain) to evaluate the effect of three soil-management systems in almond plantations: 1) minimum tillage with spontaneous vegetation strips (MTSV), 2) minimum tillage and thyme ( Thymbra capitata L.) strips (MTT), and 3) minimum tillage without plant strips (MT). The CO2 emission rates from soil presented the following increasing trend MTSV>MT>MTT, showing highly variability in the short term. Also, higher CO2 soil emissions were recorded during the spring, in contrast to autumn. Moreover, the soil- water content was the most influential environmental factor. Consequently, the use of conservation agricultural techniques such as minimum tillage and plant strips to sequester atmospheric carbon are sustainable measures for Mediterranean rainfed agro-ecosystems.

South-eastern Spain, and in particular the coastal areas of Granada and Malaga, feature a large area under subtropical crops, with orchards established on terraces built along the slopes of the mountainous areas. The climate, characterized by periodically heavy rainfall, variable in space and time, and with the common agricultural practice of leaving the taluses with bare soil, are the main factors encouraging soil erosion, runoff, and subsequent transport of pollutants. Over a two-year period, six plant covers were applied [( Thymus mastichina (Th), Lavandula dentata (La), native spontaneous vegetation (Sv), Anthyllis cytisoides (An), Satureja obovata (Sa), Rosmarinus officinalis (Ro)] in comparison to a control of bare soil (Bs) to determine the effectiveness of the covers in reducing soil erosion, runoff, and potential pollution risk by agricultural nutrients (N, P, and K) and heavy metals. Also, carbon losses were monitored in the transported sediments by runoff and in eroded soils. For this purpose, 16 m 2 erosion plots (4 m × 4 m) were laid out in the taluses of the terraces. When the yearly data were compared, the control plot (Bs) showed significantly higher soil erosion and runoff rates (26.4 t ha − 1 yr − 1 and 55.7 mm yr − 1 , respectively) than the treatments with plant covers. The plant covers studied registered the following results in runoff: Ro > Sa > An > Th ≈ La > Sv (41.7, 38.2, 35.5, 16.9, 16.1, and 12.4 mm yr − 1 , respectively) while annual soil erosion gave the following results: Sa > An > Ro > Th > Sv > La (18.0, 13.5, 13.4, 5.5, 4.4, and 3.2 Mg ha − 1 yr − 1 , respectively). This means that Sv reduced runoff and soil-erosion rates compared to Bs by not less than 78 and 83%, respectively. Nevertheless, La and Th plots were also very effective plant covers in reducing runoff and soil erosion (71.2 and 87.8; 69.5 and 79.2%, respectively) in comparison with the Bs plot. The heaviest nutrient losses in runoff and eroded soils were found in Bs and the lowest in the La, Th, and Sv plots. Bs and Ro plots registered the highest carbon losses (829.9 and 652.1 kg ha − 1 , respectively), the lowest carbon-loss rates being measured in La, Sv, and Th plots (145.2, 140.3, and 109.3 kg ha − 1 , respectively). The results indicate that heavy metals (Mn, Cr, Co, Ni, Cu, Zn, Mo, Cd, and Pb) in these types of agroecosystems may also be a potential pollutant due to transport by agricultural runoff. There was a major reduction of heavy-metal transport by plant covers in relation to the control of bare soil. The results of this research support the recommendation of using plant covers with multiple purposes (aromatic–medicinal–culinary) on the taluses of subtropical-crop terraces in order to reduce erosion and pollution risk.

Sloping and mountainous olive production systems are widespread, occupying large parts of the Mediterranean landscape prone to water erosion. Soil erosion, runoff, and soil water content patterns over a three-year period were monitored in erosion plots on a mountainside with rainfed olive ( Olea europaea cv. Picual) trees under: 1) non-tillage with barley strips of 4 m width (BS); 2) non-tillage with native vegetation strips of 4 m width (NVS); and 3) non-tillage without plant strips (NT). The erosion plots, located in Lanjaron (Granada, south-eastern Spain), on a 30% slope, were 192 m 2 in area. For assessing soil water dynamics in real-time and near-continuous soil water content measurements, multisensor capacitance probes were installed in the middle of plant strips and beneath the olive tree at five soil depths (10, 20, 30, 50, and 100 cm). The highest erosion and runoff rates were measured under NT, with a mean of 17.3 Mg ha −1 year −1 and 140.0 mm year −1 , respectively, over the entire study period. The BS and NVS with respect to the NT reduced erosion by 71% and 59% and runoff by 95% and 94%, respectively. In general, greater available soil water content was found under BS than NVS and NT, especially beneath the olive tree canopies. These results supported the recommendation of non-tillage with barley strips in order to reduce erosion and to preserve soil water for trees in traditional mountainous olive-producing areas, where orchards cover vast tracts of land.

In the Mediterranean Europe, where rainfall is scarce and irregular but often of high intensity, wild shrubs protect the soil against erosivity of raindrops. Moreover, some of these plants are the economic income for local farmers. Particularly in SE Spain, soil erosion is a core factor in environmental degradation attributed primarily to the cultivation practices and human pressure on the land. Over a four-year period, soil erosion and runoff were monitored in erosion plots on a mountainside, comparing four harvest intensities of four aromatic shrubs ( Lavandula lanata L., Santolina rosmarinifolia L. Origanum bastetanum , and Salvia lavandulifolia V.): 0% (HI-0), 25% (HI-25), 50% (HI-50), and 75% (HI-75). Also, the fresh biomass and essential-oil content were quantified in each treatment. The erosion plots were located in Lanjaron (Granada, SE Spain) on the southern flank of the Sierra Nevada Mountains, on a 20% slope, and of 96 m 2 in area. The average soil loss for HI-0, HI-25, HI-50, and HI-75 during the study period was 144.6, 187.2, 256.0, and 356.0 kg ha − 1 , respectively, and runoff 2.6, 3.2, 3.4, and 4.7 mm, respectively. The lowest average soil erosion and runoff rates for the study period were recorded with plant cover of S. lavandulifolia V. 67.6 kg ha − 1 and 1.3 mm, respectively. Since no significant differences were found between HI-25 and HI-50 for soil erosion and runoff, and harvest and distillation of wild-aromatic plants currently persists as an important economic activity in mountainous areas of the study zone, we recommend a rational harvest (HI-50), leaving the 50% of the plant biomass in the field (especially for sage and lavender) to avoid the soil degradation. In this sense, the harvest of 50% of fresh herb of sage, santolina, lavender, and oregano produced reasonable essential-oil yield of 12.7, 14.0, 19.7, and 18.3 L ha − 1 , respectively. The inappropriate harvest of aromatic plants and the intensity farming systems of mountain areas endanger land conservation, and there is an urgent need to implement appropriate land management which has a large-scale perspective but acts at the local level.

In the Mediterranean region the intensities and amounts of soil loss and runoff on sloping land are governed by rainfall pattern and vegetation cover. Over a two-year period (1998–1999), six wild species of aromatic and mellipherous plants (Thymus serpylloides subsp. Gadorensis, Thymus baeticus Boiss, Salvia lavandulifolia Vahl., Santolina rosmarinifolia L., Lavandula stoechas L. and Genista umbellata Poiret) were selected for erosion plots to determine their effectiveness in reducing water erosion on hillslopes of the Sierra Nevada Mountain (SE Spain). The erosion plots (including a bare-soil plot as control), located at 1,345 m in altitude, were 2 m2 (2 m × 1 m) in area and had 13% incline. The lowest runoff and soil erosion rates, ranging from 9 to 26 mm yr−1 and from 0.01 to 0.31 Mg ha−1 yr−1, respectively, over the entire study period, were measured under the Thymus serpylloides. Lavandula stoechas L. registered the highest rates among the plant covers tested, runoff ranging from 77 to 127 mm yr−1 and erosion from 1.67 to 3.50 Mg ha−1 yr−1. In the bare-soil plot, runoff ranged from 154 to 210 mm yr−1 and erosion from 4.45 to 7.82 Mg ha−1 yr−1. According to the results, the lowest-growing plant covers (Thymus serpylloides and Salvia lavandulifolia Vahl.) discouraged the soil erosion and runoff more effectively than did the taller and open medium-sized shrubs (Santolina rosmarinifolia L., Genista umbellata Poiret, Thymus baeticus Boiss and Lavandula stoechas L.). Monitoring allowed more direct linkage to be made between plant covers and the prevention of erosion, with implications for sustainable mountain agriculture and environmental protection.

Over a four-year period (1997–2000), soil loss and surface-runoff patterns were monitored in hillside erosion plots with almond trees under different plant-cover strips (thyme, barley and lentils) on the south flank of the Sierra Nevada (Lanjaron) in south-eastern Spain. The erosion plots (580 m a.s.l.), located on a 35 per cent slope, were 144 m2 (24 m×6 m) in area. The plant-cover strips, 3 m wide, ran across the slope. The most effective plant cover proved to be thyme, reducing soil loss by 97 per cent and runoff by 91 per cent, compared to bare soil. Barley reduced soil loss by 87 per cent and runoff by 59 per cent, compared to bare soil, while these percentages were 58 per cent and 18 per cent for lentils. Thyme proved 77 per cent more effective than barley and 93 per cent more effective than lentils in reducing soil loss; thyme was also 79 per cent more effective than barley and 90 per cent more than lentil in blocking runoff. The present study demonstrates the effectiveness of plant-cover strips in controlling soil erosion and runoff on sloping agricultural land. Copyright © 2005 John Wiley & Sons, Ltd.