Plant influence on rhizosphere hydraulic properties: direct measurements using a miniaturized infiltrometer

An infiltrometer device, 0.4 mm in radius was designed specifically to measure the hydraulic characteristics of rhizosphere soil. Its testing and application to the rhizosphere of four plant species-barley (Hordeum vulgare), oil-seed rape (Brassica napus), potato (Solanum tuberosum) and grass (Lolium multiflorum) - was described. In excavated blocks of field soil, there was a significant influence of plant species on sorptivity and water repellency in the rhizosphere. Further controlled laboratory tests on young plants in moist, sieved soil showed reduced water sorptivity owing to increased repellency in the rhizosphere compared with bulk soil for barley but not oil-seed rape. Root exudates may clog pores or become hydrophobic on soil particle surfaces. The slightly higher water repellency measured in rhizosphere soil would have minimal influence on plant water uptake. However, it may provide a buffer against desiccation at lower water contents and reduce structural degradation of rhizosphere soil by slaking.