Limited water resources in arid and semi-arid regions require innovative management to maintain crop production while minimizing the amounts of water used for irrigation. We investigated the impact of the particle size of natural clinoptilolite zeolite (CZ) on water content (WC) and hydraulic properties of a loamy sand soil. WC was measured using 5TE sensors installed at five depths (10, 20, 30, 40, and 50 cm) in soil columns (7.4 cm ID, 56 cm length). Three sizes of macro- and nano-CZ particles (20, 2.0, and 0.2 µm) were added to the soil at an application rate of 1%. The columns were subject to 14 wetting/drying cycles from 24 February to 8 December 2020. The HYDRUS-1D model was used to simulate WC and soil water storage inside the soil columns. WC increased with the decreasing particle size of CZ, especially when columns were subject to long drying periods. The larger surface area and smaller pore size of CZ altered the pore-size distribution of the loamy sand soil and increased the amount of microporosity inside the soil system, leading to increased water retention. Available water and soil water storage were increased by 3.6–14.7% and 6.8–10.5%, respectively, with larger increases with the decrease in CZ particle size. Variations in infiltration rate and hydraulic conductivity were statistically significant only with the smallest CZ particle size, with a reduction of 25.6% and 19.3% compared to the control, respectively. The HYDRUS-1D model accurately simulated WC and soil water storage, with only slight overestimation of WC (2.4%) at depths ≤ 30 cm. The results suggest that, in light-textured soils, the application of CZ in the ultra-fine nanoparticle size would increase water-holding capacity and reduce hydraulic conductivity, which would enhance the efficiency of water use and contribute to water conservation in dry regions.
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