Root decomposition affects soil hydraulic properties in four contrasting herbaceous species

Background and aims: To optimise soil conditions for agriculture and engineering, we must better understand how root growth and decomposition affect soil hydraulic properties. This paper investigates soil hydraulic properties down soil columns containing grass, forb, and legume species before and after root decomposition. Methods: Contrasting species (2 grasses, 1 forb, 1 legume) were grown within repacked soil columns. These soil columns were divided horizontally into 60 mm cores and hydraulic conductivity (Ks) was measured both before and after 7-month incubation of cores at either 5 °C or in a heated glasshouse (18–25 °C). Water sorptivity, hydrophobicity and hardness were measured in root-channel walls after decomposition in cores divided longitudinally. Soil water-release characteristics were measured in small cores sampled down the soil profile. Results: Vegetated soil averaged up to 5.6-fold greater Ks than fallow soils, varying greatly between species. Ks decreased rapidly down the columns in fallow soil, whilst D. carota and L. corniculatus soils had more uniform Ks with depth. The soil of root-channel walls showed distinct sorptivity and hydrophobicity compared to control bulk-soil. Conclusion: Appropriate species choice can increase Ks. Roots and their decomposition greatly affect these soil physical properties down the profile, influencing water dynamics in plant communities and soil-mediated ecosystem services.