Soil management and minerals drive organic carbon, nutrients and total soil element concentrations in rainfed cereal soils of Spain

Agricultural soils are currently at risk due to frequent soil disruption (tillage) and the widespread use of chemical inputs. Soils located in semiarid regions are even more fragile because they are commonly degraded. In this study, we evaluated the effects of no-till and organic farming (managed without synthetic inputs), as alternatives to conventional farming (characterized by tillage and the use of synthetic inputs), on soil properties including organic carbon (C), fertility, and total soil element concentration in rainfed cereal soils located in Spain. We also assessed the role of soil minerals and how environmental variables modulated these effects to guide management recommendations. To this end, we sampled 97 no-till and 106 organic farms, which were compared with 88 conventionally managed sites. No-till and organic farming increased soil organic C concentration by 25.5 and 13.3%, respectively, compared to conventional management. They also significantly increased total soil N and exchangeable cations (K-both, and Mg-organic farming), compared to conventional management. However, soil minerals modulated management effects, with calcite acting positively, whereas quartz and feldspars showed the opposite trend. Some soil metal concentrations were significantly reduced (Cr) and others increased (Pb, Co, Mn, Zn) under organic farming, but both no-till and organic farming increased total Fe. Latitude had a different effect on soil organic C depending on the management. Although exchangeable K decreased with latitude under the three managements, a stronger decline was observed under conventional agriculture. Higher mean temperature increased soil organic C and exchangeable K, especially under conventional agriculture, while no-till and organic farming produced more stable values (regardless of the temperature) and higher than conventional agriculture at lower temperature. Our results highlight the capacity of sustainable agricultural practices to regenerate the health (organic C) and fertility of rainfed cereal soils in Spain, and how these effects are modulated by soil minerals and environmental variables, serving as the basis for developing national-scale policies related to land management.