University of Tehran Press Iranian Journal of Soil and Water Research 2008-479X 56 4 2025 06 22 The effect of hydrochar particle size on the physical and hydraulic properties of sandy loam soil The effect of hydrochar particle size on the physical and hydraulic properties of sandy loam soil 935 948 102616 10.22059/ijswr.2025.385398.669838 FA Reza Allahi Ashlooblagh Master student, Department of Water Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 0009-0009-6208-897X Hamid Zareabayneh Professor, Department of Water Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 0000-0001-6346-2438 Atefeh Azadifar PhD student, Department of Water Science, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran. 0009-0004-6214-4445 Journal Article 2024 11 17 The conversion of plant biomass into hydrochar is recommended as a strategy to enhance the physical and hydraulic properties of soil. The objective of this study was to investigate the influence of the particle size of hydrochar from sunflower stems on physical and hydraulic properties of soil. To evaluate the physical and hydraulic characteristics of soil, a mixture of 3% by weight of three particle sizes (0-0.5, 0.5-1, and 1-2 mm) of sunflower stem hydrochar was combined with sandy-loam soil. Parameters such as bulk density, porosity, saturated moisture, field capacity, available water, permanent wilting point, discharge, velocity, hydraulic conductivity, pore-water velocity and moisture characteristics curve were measured. The results indicated that the particle size of sunflower stem hydrochar had a significant effect on the physical and hydraulic characteristics of the soil. The most influential factor on the measured parameters was the hydrochar with a particle size of 0-0.5 mm, which led to a 21.36% reduction in bulk density, and increases of 30.58%, 26.73%, 49.27%, 118.7%, and 34.10% in porosity, saturated moisture, field capacity, permanent wilting point, and available water, respectively, compared to the control soil. The application of hydrochar with a 0-0.5 mm particle size also resulted in a 65.42% reduction in discharge, velocity, hydraulic conductivity, and a 73.65% reduction in pore-water velocity compared to the control soil. Analysis of the moisture characteristics curve indicated that hydrochar increased mesopore and micropore, consequently enhancing soil water retention across various suction levels, especially at suctions ranging from 0 to 2000 cm.  The conversion of plant biomass into hydrochar is recommended as a strategy to enhance the physical and hydraulic properties of soil. The objective of this study was to investigate the influence of the particle size of hydrochar from sunflower stems on physical and hydraulic properties of soil. To evaluate the physical and hydraulic characteristics of soil, a mixture of 3% by weight of three particle sizes (0-0.5, 0.5-1, and 1-2 mm) of sunflower stem hydrochar was combined with sandy-loam soil. Parameters such as bulk density, porosity, saturated moisture, field capacity, available water, permanent wilting point, discharge, velocity, hydraulic conductivity, pore-water velocity and moisture characteristics curve were measured. The results indicated that the particle size of sunflower stem hydrochar had a significant effect on the physical and hydraulic characteristics of the soil. The most influential factor on the measured parameters was the hydrochar with a particle size of 0-0.5 mm, which led to a 21.36% reduction in bulk density, and increases of 30.58%, 26.73%, 49.27%, 118.7%, and 34.10% in porosity, saturated moisture, field capacity, permanent wilting point, and available water, respectively, compared to the control soil. The application of hydrochar with a 0-0.5 mm particle size also resulted in a 65.42% reduction in discharge, velocity, hydraulic conductivity, and a 73.65% reduction in pore-water velocity compared to the control soil. Analysis of the moisture characteristics curve indicated that hydrochar increased mesopore and micropore, consequently enhancing soil water retention across various suction levels, especially at suctions ranging from 0 to 2000 cm.  https://ijswr.ut.ac.ir/article_102616_7cb8303da1109112f488f45505122825.pdf