Assessing the Long-Term Impact of Traditional Agriculture and the Mid-Term Impact of Intensification in Face of Local Climatic Changes

In the Mediterranean basin, edaphic salinization, sodification and alkalinization related to anthropic pressures and climatic changes may hinder the ecosystem sustainability. It is pertinent to study the mid and long-term variability of these soil characteristics in face off the macro agricultural system in use (i.e., irrigation or rain-fed). Four irrigated soils from the Caia Irrigation Perimeter (Portugal), Fluvisols, Luvisols, Calcisols and Cambisols were analysed in the mid-term, from 2002 to 2012, for its available Ca²⁺, Mg²⁺, K⁺ and Na⁺ content. Overall, Ca²⁺, K⁺ and Na⁺ significantly increased during the period of this study by 25%, 8% and 7%, respectively. Soil organic matter (SOM) and pH for the irrigated soils in the area were already assessed in previous studies with the overall SOM remaining constant (p ≥ 0.05) and pH increasing (p < 0.01) by 5%. We provide the predictive maps for Na⁺ and the CROSS predictive & HotSpot evolution map from 2002 to 2012. Rain-fed soils were analysed in the long-term, from 1965 to 2012, for their SOM, pH and non-acid cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) content. While SOM, pH and the exchangeable Ca²⁺, Mg²⁺ and K⁺ significantly increased (p < 0.01) by 23%, 8%, 60%, 21% and 193%, respectively, exchangeable Na⁺ significantly decreased (p < 0.01) by 50%. These results may be related to the local climate changes as, according to the Thornthwaite classification, it went from sub-humid with great water excess (C1B2s2b4) in the climate normal 1951/1980 to sub-humid with moderate water excess (C1B2sb4) in 1981/2010 to semi-arid with little to none water excess (DB2db4) in 1991/2020. The irrigated areas in this Mediterranean region are slowly departing from sustainable goals of soil conservation and better edaphic management and conservation practices, that address the registered climatic changes in the area, could be adopted.