Irrigation reshapes weathering and pedogenesis in calcareous soils of tropical dryland (NE Brazil)

Irrigation is crucial for improving crop productivity in dryland agricultural systems. As drylands are expected to expand due to future climate scenarios, understanding the effects of irrigation on soil properties for sustainable soil management is vital. In this context, our study investigates the impact of 23 years of irrigation on the soil morphology and mineralogy of a Eutric Calcaric Cambisol in the semi-arid region of Northeastern Brazil. Two soil profiles – one irrigated (IRR) and one non-irrigated (NIRR), located 40 m apart – were studied. Detailed mineralogical analyses, including thermogravimetric analysis and X-ray diffraction modeling, and micromorphological description of thin sections were conducted. Irrigation promoted an increase in proportion of smectite layers in the soil, as evidenced by the formation of a new mixed-layer clay phase (illite–smectite). This process was probably triggered by carbonate dissolution and subsequent cationic enrichment of the soil solution. As a result, there was an increase in soil cation exchange capacity (CEC), exchangeable sodium percentage (ESP), clay activity, and K⁺ and Ca²⁺ concentrations in IRR. Regarding soil micromorphology, irrigation induced changes in the relative c/f distribution, shifting from enaulic to porphyric. The granular and moderately developed subangular blocky structure shifted to a strongly developed subangular block structure with depth, while stipple-speckled fabrics changed to striated birefringent fabrics. Our results emphasize that an increase in irrigated croplands may reshape pedogenesis and soil fertility, consequently affecting soil functioning in these dryland soils.