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Abstract: Semiarid Mediterranean climatic conditions and intensive tillage systems accelerate soil organic matter losses. Therefore, assessing agricultural practices that enhance storage of soil organic matter is needed. Stratification of soil properties with soil depth, expressed as a ratio, could indicate soil quality under different soil management. We measured soil depth stratification ratio (0–5/10–30cm and 0–5/30–50cm) of soil organic C (SOC), total N, active carbon (AC), water soluble carbon (WSC), and soil enzymatic activities [dehydrogenase activity (DHA) and β-glucosidase activity (BGA)] of a Typic Haploxerert in southern Spain. The experimental design consisted of a split–split plot design with three replications and soil properties evaluated at the end of 22 years. Tillage systems included conventional tillage (CT) and no tillage (NT). Dryland, 2-year crop rotations were wheat (Triticum aestivum L.)–fallow (WF), wheat–chickpea (Cicer arietinum L.) (WC), wheat–faba bean (Vicia faba L.) (WFb), wheat–sunflower (Helianthus annuus L.) (WS), and continuous wheat (WW). Nitrogen fertiliser rates were 0, 50 and 150kgNha−1. Stratification ratios of total N, WSC, AC, DHA, and BGA were most responsive to tillage systems; NT greater than CT. Stratification ratios of SOC, total N, WSC, AC and BGA were most responsive to crop rotation; WFb and WW greater than WF, WC, and WS. Stratification ratio of BGA was most responsive to N fertiliser rate; higher rates than no fertiliser. Stratification ratios of C and N fractions and enzymatic activities were responsive to choice of denominator used for ratio calculation. Tillage and crop rotation had more influence than N fertiliser rate in affecting stratification ratio of C and N fractions and enzymatic activities. Stratification ratio was relatively low (<2), perhaps due to the large shrinking and swelling characteristics of Vertisols. Stratification ratio of BGA was greater than of all other soil properties, suggesting that it might be a good indicator of soil quality under different soil management in Mediterranean conditions, particularly with Vertisols. This study indicated the value of stratification ratios to detect improvement in soil organic matter fractions and enzymatic activities (i.e. indicators of soil quality) with adoption of improved conservation management approaches. [Copyright &y& Elsevier]

Abstract: Studies of the impacts of the interactions of soil agricultural practices on soil quality could assist with assessment of better management to establish sustainable crop production system. The main objective was to determine the long-term effects of tillage system, crop rotation and N fertilisation on soil total N and organic C (SOC), labile fractions of organic matter (water soluble carbon, WSC, and active carbon, AC), nitrate content, and soil enzymatic activities (dehydrogenase (DHA), β-glucosidase (Glu) and alkaline phosphatase (AP)) at four different soil depths (0–5, 5–10, 10–30 and 30–50cm), in a Mediterranean dryland Vertisol in SW Spain. Tillage systems were conventional tillage (CT) and no tillage (NT). Crop rotations were wheat–sunflower (WS), wheat–chickpea (WC), wheat–faba bean (WFb), wheat–fallow (WF) and continuous wheat (WW). Nitrogen fertiliser rates were 0, 50 and 150kgNha−1. The different crop rotation systems had a great influence in soil C and N fractions and enzymatic activities. In general, the SOC, total N, WSC, and β-glucosidase contents were higher in the no tillage system than in conventional tillage system in the wheat–wheat and in the wheat–faba bean rotations at upper layer (0–5cm), while the lowest ones were obtained in the wheat–fallow rotation in both tillage systems. Carbon and N fractions, calculated by volumetric soil, showed an increase with depth in both tillage systems and in all crop rotations, which could be related to the increase of soil bulk density and soil mass with depth. The highest N fertiliser rate increased most of soil variables, especially nitrate content at deeper layers, thereby precautions should be taken with long-term N fertilisation to avoid leaching of nitrates below the tillage layer. With the exception of wheat–fallow rotation, slightly greater grain and above-ground biomass yields were obtained for wheat in NT, especially at 150kgNha−1. Combination of NT with any biannual rotation except fallow could be an adequate sustainable management in order to improve soil quality of Vertisols, under our conditions. [Copyright &y& Elsevier]