Intercropping alters rhizosphere chemistry but not early root distribution in a low phosphorus field

Background and aims: Intercropping represents an opportunity to diversify root system architectures and rhizosphere processes, optimising soil resource use, especially for nutrients with low availability. This study assessed belowground interactions in faba bean (Vicia faba) and barley (Hordeum vulgare) intercropping under marginal field conditions during early growth. Methods: Root distribution was measured to 40 cm depth, and high-resolution bio-chemical imaging visualized in situ soil pH, phosphatase activity, and P concentrations. Planar optodes, zymography, and diffusive gradients in thin films (DGT) were successively deployed in the rhizospheres of each species. Results: Soil heterogeneity (e.g., pH, phosphatase activity) strongly influenced rhizosphere processes, with acidification and alkalization observed around barley roots and varying phosphatase release. Intercropped barley showed two-fold greater pH changes but lower phosphatase activity than sole barley. Faba bean acidified its rhizosphere by only 0.10-0.17 pH units in both systems but increased its phosphatase release five-fold when intercropped. Root distribution along the soil profile was not significantly affected by intercropping at this stage. Conclusion: Our findings highlight the potential of intercropping to modulate root-driven soil processes during early growth. Extending this approach across crop development stages and intercrop systems may deliver further insights into belowground crop interactions and their relationships with nutrient acquisition in resource-limited soils.