Irrigation-driven geochemical changes regulate P fractionation in dryland soils

Phosphorus (P) availability in dryland soils is often limited due to its association with apatite and refractory forms, posing a significant challenge to agricultural productivity. This study investigated P dynamics in cultivated and uncultivated soils derived from different parent materials across two regions in the United Arab Emirates. The results confirmed that P occurs predominantly (>90%) in moderately or non-available forms, although parent material weathering and agricultural practices significantly influenced P fractionation. In soils derived from gypsum-rich aeolian sand deposits, P precipitation was primarily driven by Ca 2+ cations likely released by gypsum solubilization rather than by calcite solubilization, as suggested by the similar trend observed for gypsum, Ca P, and Ca 2+ . Irrigation with brackish water increased soil salinity and ions content, mainly Na + , which rose to 55.22 g kg −1 in the surface horizon of the cultivated soil. This accumulation may have enhanced P availability through the formation of soluble Na P compounds. On the other hand, in soils derived from alluvial material, irrigation likely induced weathering of Fe-bearing minerals, such as hornblende and chamosite, as indicated by the 1.72- to 4.26-fold higher available Fe in cultivated soil compared to uncultivated soil. The process promoted the coprecipitation of P with Fe, which account for over 30% of the total P in the surface horizon. We conclude that complex interactions between parent material, mineralogical composition, and agricultural practices govern P availability and fractionation in arid ecosystems, with implications for sustainable soil management in these areas.