生物炭添加对矿区压实土壤水力特性的影响

中国黄土高原大型露天煤矿开采导致土壤质量下降，生物炭作为环境友好型土壤改良剂，在改善农田土壤质量中应用广泛，但在有关矿区压实土壤改良的研究中不够深入。为此，该研究通过室内试验分析不同粒径的生物炭在不同添加量下对矿区排土场压实土壤水力特性的影响。试验采用4种粒径（>1～2、>0.25～1、0.10～0.25、<0.10 mm）与4种添加量（0、4、8、16 g/kg）的生物炭，设计5种压实条件（容重分别为1.3、1.4、1.5、1.6、1.7 g/cm3），并利用van Genuchten模型（VG模型）拟合土壤水分特征曲线。结果表明，添加生物炭后土壤水分特征曲线的相关系数均在0.960以上，标准差均小于0.015，说明VG模型适用于拟合添加生物炭后的土壤水分特征曲线。随着生物炭添加量的增加，土壤孔隙分布明显改变，形成了大量大孔隙和中孔隙，土壤的持水能力提高。在低容重（1.3、1.4 g/cm3）条件下，生物炭粒径越大（0.25～2 mm）添加量越高（8、16 g/kg），土壤持水、保水效果越明显；在高容重（1.5、1.6、1.7 g/cm3）条件下，小粒径（<0.25 mm）和较低的生物炭添加量（4、8 g/kg）则表现出较好的持水能力。对于不同压实条件的排土场土壤，有针对性地施用生物炭，将有效提高土壤持水保水能力，提高土壤中植物的有效利用水分。

Effects of biochar addition on the hydraulic properties of compacted soils in mining areas

Abstract: Severe soil compaction often occurs with heavy traffic during mining, particularly for a large number of large-scale opencast mines in the Loess Plateau. An important indicator, the soil hydraulic property can be widely used to measure the soil pore conditions of compacted soils. Biochar can also be added to improve the land quality for higher crop yields in farmland in recent years. The environmental soil amendment has presented higher ecological and economic benefits, due to the specific properties from the special porous structure of biochar, including the large surface area, high porosity, low bulk density, and high organic carbon contents. As such, the soil bulk density can be reduced to increase the water holding capacity in the coarse texture soil. However, only a few studies focused on the biochar addition in the soil improvement in the mining areas, especially the hydraulic characteristics of compacted soil. The purpose of this study is to evaluate the impact of addition rates and particle sizes of biochar on the soil hydraulic conductivity under various compaction conditions in a mining dump. The soil sample was collected from Datong City in Shanxi Province of China. The experiment was then carried out under the four particle sizes of biochar (1-2, 0.25-1, 0.10-0.25, and <0.10 mm) with four addition rates (0, 4, 8, and 16 g/kg) and five compaction conditions (1.3, 1.4, 1.5, 1.6, and 1.7 g/cm3). A modified van Genuchten (VG) model was also established to determine the characteristic curve of soil water. The results show that all the correlation coefficients were above 0.960, and the standard deviations were below 0.015, indicating this model suitable for the characteristic curve of soil water after the biochar addition. Most macropores and mesopores with larger pore sizes were distributed to significantly improve the water holding capacity in the field. The specific values increased from the lowest 22.74% (1.3 g/cm3, 1-2 mm, 0 g/kg) to 37.56% (1.4 /cm3, 0.25-1 mm, 16 g/kg) with the amount of biochar addition. Furthermore, the initial soil water content increased from 0.135 cm3/cm3 (1.3 g/cm3, 1-2 mm, 0 g/kg) to 0.166 cm3/cm3 (1.3 g/cm3, 1-2 mm, 8 g/kg), where the maximum increase was 0.031 cm3/cm3 in an initial soil water content. Therefore, the biochar addition greatly contributed to the water holding capacity of compacted soil with less air entry for the better use of soil water. Correspondingly, the higher capacity of water holding was obtained at the lower bulk densities (1.3 and 1.4 g/cm3), and the larger particle sizes (0.25-2 mm). A combination of parameters was achieved for the optimal water holding at the high bulk density (1.5, 1.6, and 1.7 g/cm3), lower particle sizes (<0.25 mm), and higher addition (8, 16 g/kg). Consequently, the targeted application of biochar can be widely expected to effectively improve the water holding and water retention capacity of the soils with various compaction in the mining areas. This finding can also provide a promising basis for recovery the low-quality soil.