Effects of Management and Hillside Position on Soil Organic Carbon Stratification in Mediterranean Centenary Olive Grove

The short- and medium—long-term effects of management and hillside position on soil<br> organic carbon (SOC) changes were studied in a centenary Mediterranean rainfed olive grove. One<br> way to measure these changes is to analyze the soil quality, as it assesses soil degradation degree<br> and attempts to identify management practices for sustainable soil use. In this context, the SOC<br> stratification index (SR-COS) is one of the best indicators of soil quality to assess the degradation<br> degree from SOC content without analyzing other soil properties. The SR-SOC was calculated in soil<br> profiles (horizon-by-horizon) to identify the best soil management practices for sustainable use. The<br> following time periods and soil management combinations were tested: (i) in the medium-long-term<br> (17 years) from conventional tillage (CT) to no-tillage (NT), (ii) in the short-term (2 years) from CT<br> to no-tillage with cover crops (NT-CC), and (iii) the effect in the short-term (from CT to NT-CC) of<br> different topographic positions along a hillside. The results indicate that the SR-SOC increased with<br> depth for all management practices. The SR-SOC ranged from 1.21 to 1.73 in CT0, from 1.48 to 3.01 in<br> CT1, from 1.15 to 2.48 in CT2, from 1.22 to 2.39 in NT-CC and from 0.98 to 4.16 in NT; therefore, the<br> soil quality from the SR-SOC index was not directly linked to the increase or loss of SOC along the<br> soil profile. This demonstrates the time-variability of SR-SOC and that NT improves soil quality in<br> the long-term.