Phosphorus Lability and Desorption Kinetics Across a Traditional Date Palm Soil Catena in Oman

Phosphorus (P) is a critical yet often limited macronutrient in plant nutrition due to its complex chemistry and restricted bioavailability in soils. This study investigated the P status and (de)sorption kinetics in arid salt-affected soils along a 40 km transect in the Al-Batinah region of Oman, extending from the coast to the mountains (altitude range: 5-334 m above mean sea level (mamsl)). Soil samples were characterized, and P lability and desorption kinetics were assessed using a combination of diffusive gradients in thin films (DGT), diffusive equilibrium in thin films (DET), and the DIFS model. Coastal soils exhibited the highest P levels, with Olsen-P and water-soluble P averaging 53 and 2.4 mg kg- 1, respectively, compared to 29 and 0.97 mg kg- 1 at altitudes above 100 mamsl. Soil solution P (DET) and DGT-labile P concentrations were also highest at the coastal sites. Desorption kinetic parameters and the relative contribution of desorption to soil solution P replenishment after DGT-induced depletion were strongly correlated with calcium carbonate (CaCO3) concentrations, highlighting CaCO3 as the main driver of P bioavailability in these soils. This study extends the application of DGT/DET-DIFS methodology and indicates that P bioavailability in the surveyed soils is largely governed by adsorption on CaCO3 precipitates, rather than by organic colloids or aluminosilicates. Despite the elevated coastal soil salinity, its impact on P desorption kinetics or bioavailability appeared negligible. These findings offer insights into P dynamics in arid salt-affected soils.