Effect of agricultural practices and coastal constraints on soil microbial functional properties in Mediterranean olive orchards

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Abstract

Summary

This research examines how agricultural practices commonly used in Lebanese olive tree orchards (no-tillage, co-culture with Vicia sativa L. var. sativa and conventional tillage) affect soil microbial and chemical characteristics, and whether this depends on geographical context (coastal or inland areas). Four coastal and four inland sampling sites were selected, and at each site three practices were considered (one practice per plot). For each plot (200 m2), 20 soil samples were taken and homogenized to obtain a composite sample from which soil was characterized chemically and microbiologically. Differences in chemical properties (smaller N content and alkyl C fraction in the coastal area) depended on geographical location rather than on agricultural practices. For microbial properties, catabolic structure varied with geographical location; the index of catabolic diversity was larger in the coastal area. Importantly, the basal respiration was similar in both areas although the soil contained less nitrogen (N) in the coastal area. The negative effect of conventional tillage on microbial functioning of the soil was observed only in relation to geographical location. We found that this effect was reduced by co-culture, for example with Vicia sativa L. var. sativa. Our study reveals that geographical location affects how agricultural practices affect soil properties (in the coastal area, enhanced mineralization of labile C and change in microbial catabolic profile). This suggests that soil management should take into account the environmental conditions specific to coastal areas, which enhance the adverse effects of conventional tillage. Consequently, this type of management should not be implemented in coastal areas of the Mediterranean.

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