Land use and management effects on carbon and nitrogen in Mediterranean Cambisols

In Mediterranean Europe, dehesa is the most widespread agroforestry system, that integrates forestry with agricultural and livestock management practices. It is characterized by the conservation of forest oaks to provide environmental services including carbon capture and storage. During the past two decades, many dehesa areas have been converted to olive groves with little information regarding long-term effects on soil organic carbon (SOC) distribution, total nitrogen (TN) concentrations, C:N relation, or stratification ratios (SR) throughout the soil profile. Understanding carbon and nitrogen dynamics is essential for making appropriate land management decisions. Our objective was to qualify SOC, TN, and profile SRs after Eutric Cambisols were converted from dehesa to olive groves using organic or conventional management practices for approximately 20 years. We analyzed soil profile samples from 45 farms in 2009 in Southern Spain. Olive groves managed using organic practices had more SOC stock (73.58 Mg ha−1) and TN stock (7.10 Mg ha−1) than dehesa. SOC and TN decreased with depth under both land uses and managements. Overall, organic farming (OF) resulted in higher SOC and TN levels than conventional tillage (CT), but the SRs were similar for both land uses and management strategies. These results suggest that, in general, these soils do not have degradation problems. Only in SR2 (defined by Ap-A/C) of SOC and SR2 of TN, showed significant differences and soils under OF had higher quality than under CT. By contrast, the C:N stratification ratio was similar in all land uses and management.