Biochar is a stable carbon-rich product obtained through pyrolysis of plant and animal-based biomass. Soil is often amended with biochar due to the beneficial features, such as carbon sequestration, improvement of crop growth and yield by enhancing soil fertility, removal of an organic and inorganic pollutant from the soil, and improvement of water retention properties of the soil. Fundamentally, the amendment of soil with biochar alters the soil water retention characteristics (SWRC) of the soil. This is primarily due to the inherent properties of biochar that includes large specific surface area (SSA) by the intra-particle pores, and the functional groups present in biochar surface. SWRC is vital for both agricultural soil and soil in geotechnical or geo-environmental engineering structures due to the presence of vegetation. The effect of biochar on the SWRC of agricultural soil was extensively studied. However, it is rarely studied for soil in geotechnical or geo-environmental engineering structures, such as landfill cover, bioengineered slope, embankment, green roof, etc. Soil in these structures subjects to a distinct condition, in terms of compaction state and design life compared to agricultural soil. Therefore, a comprehensive gathering of information on the effect of biochar on the SWRC and the factors controlling the biochar influence is needed for potential investigation and application of biochar amendment for soil in geotechnical or geo-environmental engineering structures. In this article, the effect of biochar amendment on the SWRC of soil has been reviewed and summarized by considering various factors controlling the influence of biochar on the SWRC. The literature review revealed that the amendment of soil with biochar could improve the SWRC while few occasions not influence the SWRC. Factors, such as feedstock type and pyrolysis temperature, particle size of biochar, soil type, and compaction state have strong bearing on the influence of biochar on the SWRC.

Biochar是一种稳定的富含碳的产品，可通过植物和动物类生物质的热解获得。由于有益的特性，例如碳固存，通过提高土壤肥力来改善作物生长和产量，从土壤中去除有机和无机污染物以及改善土壤的保水特性，经常用生物炭对土壤进行改良。从根本上说，用生物炭对土壤进行改良会改变土壤的土壤保水特性（SWRC）。这主要归因于生物炭的固有特性，该特性包括通过颗粒内孔的大比表面积（SSA），以及生物炭表面中存在的官能团。由于存在植被，SWRC对于农业土壤以及岩土或地球环境工程结构中的土壤都至关重要。广泛研究了生物炭对农业土壤SWRC的影响。但是，很少对岩土工程或地球环境工程结构中的土壤进行研究，例如垃圾掩埋场，生物工程边坡，路堤，屋顶绿化等。这些结构中的土壤在压实状态和设计寿命方面受到不同的条件与农业土壤相比。因此，需要全面收集有关生物炭对SWRC的影响以及控制生物炭影响的因素的信息，以便进行岩土工程或地球环境工程结构中土壤生物炭改良剂的潜在研究和应用。在本文中，通过考虑控制生物炭对SWRC影响的各种因素，对生物炭改良剂对土壤SWRC的影响进行了综述和总结。文献综述显示，用生物炭改良土壤可以改善SWRC，而很少有情况不影响SWRC。原料类型和热解温度，生物炭的粒径，土壤类型和压实状态等因素对生物炭对SWRC的影响有很大关系。