The physical properties of biochar have been shown to dramatically influence its performance as a soil amendment. This study assessed the role of biochar particle size and hydrophobicity in controlling soil water movement and retention. Softwood pellet biochar in five particle size ranges (>2 mm, 2–0.5 mm, 0.5–0.25 mm, 0.25–0.063 mm and <0.063 mm) was used for the experiment. These particle sizes were tested on two soil types (sandy loam and loamy sand) at four different application rates (1, 2, 4 and 8%) in the laboratory. Soil water suction at wet range and dry range were measured using the Hyprop and WP4-T, respectively. From this, the moisture content at field capacity ($\theta$_fc), permanent wilting point ($\theta$_pwp) and plant available water ($\theta$_awc), were determined. Saturated hydraulic conductivity (K_sat) was measured using the KSAT device and biochar hydrophobicity was determined using the ethanol drop test method. Our results showed that biochar hydrophobicity increased with decreasing biochar particle size, leading to a reduction in its water retention capacity. The highest $\theta$_fc (0.087 cm⁻³ cm⁻³) and $\theta$_awc (0.064 cm⁻³ cm⁻³) were observed for soils amended with >2 mm biochar. The soil hydraulic conductivity increased with decreasing biochar particle sizes, with the exception of <0.063 mm biochar, which showed a significant (p ≤ 0.05) decrease in soil hydraulic conductivity compared to the larger particle sizes. The results clearly showed that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affected mainly hydraulic conductivity; both interpores and intrapores controlled soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended.

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生物炭粒径和疏水性在改善土壤水力特性中的作用

生物炭的物理特性已被证明显着影响其作为土壤改良剂的性能。本研究评估了生物炭粒径和疏水性在控制土壤水分运动和保留中的作用。五个粒度范围（>2 mm、2-0.5 mm、0.5-0.25 mm、0.25-0.063 mm 和 <0.063 mm）的软木颗粒生物炭用于实验。在实验室中以四种不同的施用率（1%、2%、4% 和 8%）在两种土壤类型（砂壤土和壤土沙）上测试了这些粒径。分别使用 Hyprop 和 WP4-T 测量湿区和干区的土壤吸水量。由此，田间持水量的水分含量（$\theta$_fc ), 永久萎蔫点 ($\theta$_pwp ) 和植物有效水 ($\theta$_awc），已确定。使用 KSAT 装置测量饱和水力传导率 (K _sat )，并使用乙醇滴测试方法确定生物炭疏水性。我们的研究结果表明，生物炭的疏水性随着生物炭粒径的减小而增加，导致其保水能力降低。最高的$\theta$_fc (0.087 cm ^-3  cm ^-3 )和$\theta$_awc (0.064 cm ^-3  cm ^-3 ) 对于用>2 mm biochar 修正的土壤进行了观察。土壤导水率随着生物炭粒径的减小而增加，但<0.063 mm的生物炭除外，其表现出显着的（p ≤ 0.05) 与较大粒径相比，土壤水力传导率降低。结果清楚地表明，生物炭内孔隙度（生物炭颗粒内部的孔隙）和孔隙度（生物炭和土壤颗粒之间的孔隙空间）都是影响土壤水力特性的重要因素。生物炭间孔主要影响导水率；孔间和孔内都控制土壤保水性。我们的研究结果表明，为了更有效地增加粗糙土壤的土壤保水性，建议使用具有高孔隙率的亲水性生物炭。