Micro- and macro-scopic investigations on wheat-induced change of soil water retention curve of a compacted loam

Plant-soil interaction is of great concern in the field of agriculture and geotechnical engineering such as green slope and evapotranspiration landfill cover. Soil water retention curve (SWRC) is an essential soil hydraulic property which not only determines the amount of water available in soil for plant growth, but also the magnitude of soil suction that attributes to shear strength of unsaturated soil and consequently the stability of unsaturated soil slope. Recent studies have investigated the difference of SWRC between planted soil (i.e. soil with plant roots) and bulk soil (i.e. soil without plant roots but near roots), but seldom study investigates the difference of SWRC between planted soil and unplanted soil (i.e. soil that is completely isolated with plant roots) from both micro- and macro-scopic perspectives. This study aims to investigate the wheat-induced change of SWRC from micro- and macro-scopic perspectives. SWRC of wheat-planted soil and unplanted were measured by the simplified evaporation method. Then pore size distribution (PSD) of wheat-planted soil and unplanted soil were measured by mercury intrusion porosimetry (MIP) test. The results showed that wheat-planted soil had larger saturated volumetric water content (s) than that of unplanted soil, which can be explained by the results of PSD that wheat-planted soil had larger void ratio (e) than that of unplanted soil. Compared with unplanted soil, wheat-planted soil had more volume of pore in diameter from 1 to 20 μm which is corresponding to suction range from 10 to 100 kPa. Thus wheat-planted soil had larger absorption rate of SWRCs than that of unplanted soil in suction range from 10 to 100 kPa. The above findings could enhance our understanding of the mechanism of root-soil interaction.