Soil phosphorus in arid agriculture: The riddle beneath our feet: Opinion Paper

Phosphorus (P) remains a persistent nutritional constraint in agriculture despite the accumulation of substantial native and fertilizer-derived P reserves in many cultivated soils. This contradiction is particularly pronounced in hot arid regions, where crops frequently experience P deficiency despite the presence of appreciable total and residual soil P. This opinion paper argues that the central challenge is not simply P scarcity, but P accessibility, governed by the interaction of alkaline soil chemistry, calcium carbonate, low organic carbon, moisture limitation, restricted diffusion, and weak biological turnover. In calcareous soils, soluble orthophosphate may progressively enter calcium-associated pools, to precipitate rapidly with calcium carbonate or sorb onto mineral surfaces forming insoluble calcium phosphate compounds while carbon and water limitations restricting ion diffusion as well as constrain microbial mineralization and rhizosphere-mediated mobilization. Thus, the conventional strategy of repeatedly increasing soluble P inputs may enlarge soil P stocks without proportionately improving crop acquisition. We propose a conceptual shift from chemical saturation to ecological mobilization, supported by three complementary strategies: (i) biological acceleration through native phosphate-solubilizing microorganisms, root mediated organic acids and arbuscular mycorrhizal fungi; (ii) rebuilding the organic and biological components of the P cycle through organic amendments, humic acids, biochar and adapted vegetation; and (iii) precision spatial and temporal synchronization of P supply with root activity and soil moisture. The paper further emphasizes that residual soil P is not a homogeneous reserve: its contribution depends on the balance between mineral stability, release kinetics, diffusion, biological transformation, and plant uptake. Future research should, therefore, move beyond static estimates of available P toward fraction-specific and process-oriented assessment of P accessibility. For hot arid agroecosystems, sustainable P management will require integrating fertilizer inputs with the biological and ecological processes that govern the mobilization and recycling of existing soil P reserves.