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<p>Olive orchards in semiarid areas are maintained under bare soil conditions, with significant effects on soil properties. This study examined the roles of orchard age (OA) and Cropping System (CS) based on Cover crop (CC) on Soil Organic Carbon (SOC), Bulk Density (BD), and other soil traits in a semi-arid region of Tunisia. Two olive orchards 50 and 15 years old respectively, subjected to tillage were investigated. The CS consisted of 3 contrasting CC treatments: faba bean (FB) CC, vetch-oat (VO) intercrop CC, and bare soil (NC) as a control. Samples were taken below the olive canopy (0–30&#xa0;cm) layer. The experimental design was a split-plot with orchard age as a main plot. Non-correlated variables at |r| &gt; 0.7 were selected, standardized, and included in a specific multivariate analysis namely canonical discriminant analysis (CDA) to capture the multivariate effect of treatments on the variability and the relationship among variables. A general linear mixed model checked the response variable differences by the treatments and interaction of each variable. A negative correlation was found between SOC and BD (<i>r</i> = -0.98). No significant effects of the CS were detected for individual soil variables and most variables, including soil texture, were not significantly affected by OA. Significant differences associated with OA were observed only for CaCO₃, Ca, and assimilable P, which were higher in the older orchard and may reflect differences in long-term management history (e.g., fertilization and erosion processes) rather than OA alone. The CDA yielded one significant CDA axis explaining 80.9% of the total variability, showing that soil variability was more strongly associated with differences between orchards of contrasting age and management history than with short-term CC treatments. CC effects were weak, inconsistent, and not clearly detectable across all treatment combinations, as illustrated by the lack of separation between the young NC orchard and both old NC and FB orchards. Multivariate analysis revealed only slight and inconsistent patterns related to CC treatments, rather than robust shifts in soil properties. Lastly, the CDA unveiled similar behaviours of P, Mg, and Ca on one side, and SOC, EC, and pH on the other, suggesting associations with nutrient management history and general soil properties rather than clear CC effects In conclusion, SOC did not differ significantly between orchards despite long-term tillage, and short-term CC effects were limited. These findings indicate that observable improvements in soil quality may require longer-term implementation and/or more diverse CC mixtures under semi-arid conditions.</p> Graphical Abstract <p></p> <p>The graphical abstract summarizes the experimental framework, analytical approach, and key findings of a study conducted in a semi-arid olive orchard system in Siliana, northwest of Tunisia. Soil samples were collected from the 0–30&#xa0;cm layer in two orchards of contrasting age (50 and 15 years old) to assess how OA and short-term CC management are associated with soil physicochemical variability. Two CC systems, vetch oat and faba beans, were compared using multivariate statistical tools, particularly CDA, to capture subtle treatment related patterns. The results indicate that differences between orchards of contrasting age were the main source of variation in soil properties, exceeding the short-term influence of CC. However, these differences likely reflect the combined effects of OA and site-specific management history. Young orchards showed more distinct multivariate response particularly under vetch-oat CC, suggesting a higher sensitivity to recent management practices. In contrast, the older orchard was associated with higher phosphorus and calcium levels, which may be related to long-term nutrient accumulation and legacy management effects. A strong negative correlation between SOC and BD highlights the role of soil organic matter (SOM) in improving soil physical structure and fertility. Although short-term CC effects on individual soil parameters were limited, multivariate analysis revealed detectable shifts in soil functioning. These findings emphasize the importance of considering OA as a proxy for long-term soil processes, while acknowledging the influence of site history, when designing sustainable orchard management strategies aimed at enhancing soil health, nutrient cycling, and long-term agroecosystem resilience under semi-arid conditions.</p>

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Results of 50 Years of Soil Management with Cover Crops’ Effect on Physical and Chemical Traits in Olive Orchards in the Northwest of Tunisia: Multivariate Soil Responses to Olive Orchard Age

  • 期刊论文

  • 发表日期：

    2026年5月29日

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  • Farah Mlaiki,
  • Imene Dridi,
  • Ahlem Tlili,
  • Calogero Schillaci,
  • Sergio Saia

摘要

Olive orchards in semiarid areas are maintained under bare soil conditions, with significant effects on soil properties. This study examined the roles of orchard age (OA) and Cropping System (CS) based on Cover crop (CC) on Soil Organic Carbon (SOC), Bulk Density (BD), and other soil traits in a semi-arid region of Tunisia. Two olive orchards 50 and 15 years old respectively, subjected to tillage were investigated. The CS consisted of 3 contrasting CC treatments: faba bean (FB) CC, vetch-oat (VO) intercrop CC, and bare soil (NC) as a control. Samples were taken below the olive canopy (0–30 cm) layer. The experimental design was a split-plot with orchard age as a main plot. Non-correlated variables at |r| > 0.7 were selected, standardized, and included in a specific multivariate analysis namely canonical discriminant analysis (CDA) to capture the multivariate effect of treatments on the variability and the relationship among variables. A general linear mixed model checked the response variable differences by the treatments and interaction of each variable. A negative correlation was found between SOC and BD (r = -0.98). No significant effects of the CS were detected for individual soil variables and most variables, including soil texture, were not significantly affected by OA. Significant differences associated with OA were observed only for CaCO₃, Ca, and assimilable P, which were higher in the older orchard and may reflect differences in long-term management history (e.g., fertilization and erosion processes) rather than OA alone. The CDA yielded one significant CDA axis explaining 80.9% of the total variability, showing that soil variability was more strongly associated with differences between orchards of contrasting age and management history than with short-term CC treatments. CC effects were weak, inconsistent, and not clearly detectable across all treatment combinations, as illustrated by the lack of separation between the young NC orchard and both old NC and FB orchards. Multivariate analysis revealed only slight and inconsistent patterns related to CC treatments, rather than robust shifts in soil properties. Lastly, the CDA unveiled similar behaviours of P, Mg, and Ca on one side, and SOC, EC, and pH on the other, suggesting associations with nutrient management history and general soil properties rather than clear CC effects In conclusion, SOC did not differ significantly between orchards despite long-term tillage, and short-term CC effects were limited. These findings indicate that observable improvements in soil quality may require longer-term implementation and/or more diverse CC mixtures under semi-arid conditions.

Graphical Abstract

The graphical abstract summarizes the experimental framework, analytical approach, and key findings of a study conducted in a semi-arid olive orchard system in Siliana, northwest of Tunisia. Soil samples were collected from the 0–30 cm layer in two orchards of contrasting age (50 and 15 years old) to assess how OA and short-term CC management are associated with soil physicochemical variability. Two CC systems, vetch oat and faba beans, were compared using multivariate statistical tools, particularly CDA, to capture subtle treatment related patterns. The results indicate that differences between orchards of contrasting age were the main source of variation in soil properties, exceeding the short-term influence of CC. However, these differences likely reflect the combined effects of OA and site-specific management history. Young orchards showed more distinct multivariate response particularly under vetch-oat CC, suggesting a higher sensitivity to recent management practices. In contrast, the older orchard was associated with higher phosphorus and calcium levels, which may be related to long-term nutrient accumulation and legacy management effects. A strong negative correlation between SOC and BD highlights the role of soil organic matter (SOM) in improving soil physical structure and fertility. Although short-term CC effects on individual soil parameters were limited, multivariate analysis revealed detectable shifts in soil functioning. These findings emphasize the importance of considering OA as a proxy for long-term soil processes, while acknowledging the influence of site history, when designing sustainable orchard management strategies aimed at enhancing soil health, nutrient cycling, and long-term agroecosystem resilience under semi-arid conditions.