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Surface soil hydraulic properties play critical roles in controlling water infiltration, evaporation, and soil water storage, in‐turn affecting the evolution of soil pore structure in cultivated desert soils of arid areas. The variability in soil pores and hydraulic properties caused by conversion of native semidesert soils to agroforestry use alters soil water storage and water budget in the desert–oasis ecotone. The objective of this study was to investigate that land use conversion alters surface soil hydraulic properties and enhances the contribution of soil macropores to water flow in the Linze desert–oasis ecoregion. Water infiltration and soil pores characteristics with nine replicates were measured using a disc tension infiltrometer across four habitat types (Haloxylon ammodendron shrublands, Populus gansuensis forests, Medicago sativa Linn grasslands, and Zea mays croplands) during the growing season. Soil properties and hydraulic conductivity characteristics clearly varied across the four habitat types. Saturated hydraulic conductivity was 0.177, 0.126, 0.118, and 0.031cm min−1  in the forest, grassland, shrubland, and cropland, respectively, with the corresponding average soil moisture being 7.6, 6.7, 0.9, and 19.2%. Clay content, bulk density, and initial soil moisture were the key soil physicochemical properties affecting saturated hydraulic conductivity (Ks). The macropores (> 0.5 mm in radius) accounted for 15–60% of total water flow, while 0.25–0.5 mm pores contributed to 12–24% across the four habitat types. The contribution of >0.5 mm pores to water flow in the forest was 3.3–4.0‐times greater than in shrubland and cropland, due to greater soil macroporosity (58 cm−3 cm3 ) and undisturbed soil pore structure. Land use conversion has a positive impact on soil properties, structure features, and soil hydraulic properties, and as a consequence, enhance the complexity of water exchange in the arid areas.

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The characteristics of soil macropores and water infiltration are closely connected to the growth of plant roots and their root zone environment. However, it is unclear how the root zone environment of oasis farmlands regulates the development of soil macropores and water flow in hyper‐arid regions. The objective of this study was to investigate soil macropores and their effect on water flow under irrigated oasis farmlands using a combination of X‐ray computed tomography (CT) and dye tracer. It was hypothesized that the integration of CT and dye tracer could clearly reveal preferential flow through biopores and large pores of oasis soils. A helical medical CT scanner was used to quantify more information about soil macropores in the root zone, along with an in situ single‐ring dye infiltration experiment to reveal water flow in three different oasis farmlands (piedmont oasis farmland, marginal oasis farmland, and old oasis farmland). Soil macroporosity was 0.44% under crop rows, while soil macroporosity in the interrows was only 0.30% across the oasis farmlands. Biopores contributed 73% of the volume of the total macropores under crop rows. The stable infiltration rate in the interrows was 0.3 mm min−1, which was significantly (p < 0.05) less than that under crop rows (0.7 mm min−1). Water flow under crop rows were mainly transported in biopores and large pores. The contribution of macropores to preferential flow under crop rows was 4.8 times larger than interrows. The integration of CT and dye tracer was a more holistic technique, which adequately revealed that oases had preferential flow affected by biopores and large pores, resulting in higher solute and contaminant transport. Key Points Soil macropores and preferential flow affected by crop roots were investigated in hyper‐arid regions. The integration of CT and dye tracer adequately identified preferential flowpaths of oasis soils. Biopores were larger under crop rows than interrows. Preferential flow transported in biopores and large soil pores under crop rows.

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