Despite the known benefits of biochar application to soils, little is known about its effect on soil wettability and the consequences on soil water movement across the soil profile. Focusing on the latter, three types of commercial biochar derived from wheat, corn, and rice straw produced under low temperature (350–450 ℃) were mixed with a wettable sandy soil at rates of 0%, 2%, 5%, and 10% w/w. Soil water repellency (SWR) of the biochars and biochar–soil mixtures was determined by water drop penetration time (WDPT) test and sessile-drop contact angle (CA) measurement. The WDPT results (< 5 s) showed complete wettability for the biochar–soil mixtures, whereas CA results indicated some water repellency. The mean initial CA of the three biochars varied between 105.3° and 113.9°, with ∼ 30° for the pure sand, and between 56.8° and 75.7° for the biochar–soil mixtures. SWR increased with biochar-application rate, whereas biochar particle size (< 1 mm and > 1 mm) had no significant effects on SWR. A 2-D flow chamber experiment with point source water application at the surface was used to continuously monitor the flow pattern and soil water content (SWC) distribution across the soil profile during infiltration and redistribution periods. Biochar–soil mixtures (2% and 5% w/w) with the three biochar types were studied. Flow chamber results showed substantial differences in plumes shape and internal SWC distribution in the biochar–soil mixtures compared to the untreated sand during the wetting and drainage. The plumes' shape and nonmonotonic spatial SWC distribution suggested unstable flow in the biochar–soil mixtures. The internal fingers developed in the biochar treated sand indicate that SWR induced by biochar addition seemed to be physically induced via the blending of the biochar and soil particles, rather than chemically induced, via coating of the soil particles with amphiphilic molecules. Under field conditions, the primary and inner finger-like plumes may eventually form preferential flow paths that will affect the spatial distribution of water and fertilizer in soil profiles and their availability to plant roots.

尽管已知将生物炭应用于土壤的好处，但对其对土壤润湿性的影响以及对土壤剖面上土壤水分运动的影响知之甚少。以后者为重点，将低温（350-450 ℃）下生产的小麦、玉米和稻草三种商业生物炭与可湿性沙土以 0%、2%、5% 和 10% 的比例混合。 % w/w。生物炭和生物炭-土壤混合物的土壤斥水性 (SWR) 通过水滴渗透时间 (WDPT) 测试和固着滴接触角 (CA) 测量来确定。WDPT 结果 (< 5 s) 表明生物炭-土壤混合物具有完全的润湿性，而 CA 结果表明具有一定的防水性。三种生物炭的平均初始 CA 在 105.3° 和 113.9° 之间变化，纯沙约为 30°，在 56.8° 和 75 之间。生物炭-土壤混合物为 7°。SWR 随着生物炭施用率的增加而增加，而生物炭粒径（< 1 mm 和 > 1 mm）对 SWR 没有显着影响。在地表点源水应用的二维流动室实验用于在渗透和再分配期间连续监测整个土壤剖面的流动模式和土壤含水量 (SWC) 分布。研究了三种生物炭类型的生物炭-土壤混合物（2% 和 5% w/w）。流室结果显示，与润湿和排水过程中未处理的沙子相比，生物炭-土壤混合物中的羽流形状和内部 SWC 分布存在显着差异。羽流的形状和非单调的空间 SWC 分布表明生物炭-土壤混合物中的流动不稳定。在生物炭处理过的沙子中形成的内指表明，添加生物炭引起的 SWR 似乎是通过生物炭和土壤颗粒的混合来物理诱导的，而不是通过用两亲分子涂覆土壤颗粒来化学诱导的。在田间条件下，初级和内部指状羽流最终可能形成优先流动路径，这将影响土壤剖面中水和肥料的空间分布及其对植物根系的可用性。