A new and simple hydraulic characteristic model of unsaturated rooted soils considering pore creation and non-uniform pore occupation

Plant roots affect water retention curve (WRC) and hydraulic conductivity function (HCF) of soils through interaction with their pore structure. The current WRC equations of rooted soils primarily consider uniform pore occupation by roots, even though many studies confirmed that roots occupy only certain macro-pores and at the same time would potentially create new macro-pores. Moreover, equations for capturing root effects on HCF are rare. In this study, a new and simple hydraulic characteristic model (including WRC and HCF) was proposed for unsaturated rooted soils based on the fractal theory. The new model is capable of capturing two important physical processes related to the alteration of pore structure by roots with: nonuniform pore occupation and creation of new macro-pores. Six parameters were needed in the new model, three of which were used to describe the alteration of pore structure by roots, while the other three were for describing the hydraulic properties of bare soils. Validation against seven sets of existing test data demonstrates that the new model performs well in the prediction of WRCs and HCFs of bare and rooted soils with varying soil textures, initial void ratios, suction ranges, and planting conditions.