Résumé
Phosphorus (P) is a key nutrient that limit plant productivity in alkaline-calcareous soils due to sorption and precipitation. Thus, selecting appropriate P sources and understanding the rhizosphere’s role in P uptake is essential. A greenhouse experiment was conducted using white lupin to evaluate the impact of four P sources added to alkaline soil (pH = 8.77): Rock phosphate (RP), Orthophosphate (Ortho), Polyphosphate (Poly), and Triple superphosphate (TSP) compared to a control (soil background P) on various parameters including rhizosphere and bulk soil enzyme activities, pH and bioavailable P, root morphology, root exudates, plant biomass and P uptake in shoots and roots.
Significant differences among P sources were observed in their effects on plant biomass and rhizosphere biochemistry. The RP treatment resulted in a 37 % increase in root-to-shoot ratio compared to the control (p < 0.05), with both showing similar root morphological traits. In contrast, Ortho and TSP led to reductions in most root parameters, except for average root diameter that increased by 14 % and 21 %, respectively. Poly showed the highest (p < 0.05) shoot dry biomass. Acid phosphatase activity was significantly higher in rhizosphere soil relative to bulk soil across all treatments, with highest level under RP (p < 0.05). Alkaline phosphatase activity remained unchanged in the rhizosphere but was higher (p < 0.05) in bulk soil treated with soluble P sources. Rhizosphere soil pH declined significantly under RP and the control compared to the rest of the treatments (p < 0.01). The composition and concentration of organic anions (OAs) varied depending on the P source. Under RP, citric acid was predominant, whereas oxalic acid was more prevalent across other treatments. Notably, shoot P uptake was negatively correlated with total OAs, following a polynomial regression model (R2 = 0.65, p = 0.005). The study demonstrates that P uptake is governed by a dynamic interaction between soil chemistry, the nature of P source, and rhizosphere-mediated strategies that respond distinctly depending on the source of P. Polyphosphate showed the best performance due to its solubility and slow hydrolysis features compared to the calcium phosphate fertilizers.