Phosphorus acquisition processes in the field: study of faba bean cultivated on calcareous soils in Algeria

Little is known about the occurrence of phosphorus (P) acquisition processes in the field, especially for faba bean (Vicia faba L.) in calcareous soils. We sampled soil, rhizosphere and plant materials in 12 calcareous field sites in Algeria and performed physicochemical analysis during two growing seasons. Both proton exudation and root exploration increased in P-deficient soils as compared to P-sufficient soils. Inhibition of nitrogen (N) fixation and rhizosphere alkalization were observed in N-rich soils. We also found that calcium (Ca) concentrations in both shoots and roots significantly increased with P-deficiency. The same trend, although less significant, was observed with respect to Ca uptake. These field observations suggested that acidifying roots acquired P from dissolving Ca-P minerals. The concomitant increase of the ratio Ca/P uptake should further enhance their dissolution. Other rhizosphere processes such as the mineralization of organic P should control P acquisition as alkalization occurred in the root zone in response to the inhibition of N fixation. In conclusion, P-acquisition processes in the field were consistent with previous findings made at the laboratory. In addition, the variety of faba bean cultivated by local farmers appeared relatively well adapted to field conditions thanks to the deployment of rhizosphere processes. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.