Besides its carbon (C) sequestration potential, biochar is being promoted as an amendment to improve soil quality. Burying biochar in soils is known to affect soil physical quality in the short-term (<5 years), although the intensity of these effects depends on soil texture and biochar concentration especially. However, the long-term effects of biochar remain largely unknown, yet are important to quantify given biochar's persistency in soils. The objective of this study was therefore to assess the long-term effect of biochar on physical properties as a function of biochar concentration for soils with differing textures. For this purpose, soil physical properties were measured in the topsoil of three fields (silt loam, loam and sandy loam textures) in Wallonia (southern Belgium) presenting former kiln sites containing charcoal more than 150 years old. Particle density and bulk density slightly decreased as a function of charcoal-C content but the presence of charcoal in kiln sites did not affect total porosity. The water retention curve measurements revealed that water content was mostly affected in the mesopore range by the century-old charcoal-C content. This effect was strongest for the sandy loam. On the other hand, the presence of century-old charcoal increased the hydraulic conductivity for pF values between 1.5 and 2 for the silt loam, whereas no effect of charcoal was observed for the loamy and sandy loam soils. Results are discussed with respect to biochar characteristics and the various ways in which biochar particles could be distributed within soils. Overall, the present study highlights a limited effect of century-old charcoal on the pore size distribution (at constant porosity) and on the resulting soil physical properties.

中文翻译：

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生物炭对瓦隆（比利时）工业化前炭窑遗址不同质地农业土壤物理性质的长期影响

除了碳 (C) 封存潜力外，生物炭还被推广为改善土壤质量的改良剂。众所周知，将生物炭埋入土壤中会在短期（<5 年）内影响土壤物理质量，尽管这些影响的强度尤其取决于土壤质地和生物炭浓度。然而，生物炭的长期影响在很大程度上仍然未知，但鉴于生物炭在土壤中的持久性，量化它很重要。因此，本研究的目的是评估生物炭对不同质地土壤的生物炭浓度作为生物炭浓度函数的长期影响。为此，测量了三个田地表土（粉砂壤土、瓦隆（比利时南部）的壤土和沙壤土质地）展示了含有 150 多年历史的木炭的前窑址。颗粒密度和堆积密度随木炭-C 含量的变化而略有下降，但窑址中木炭的存在不影响总孔隙率。保水曲线测量表明，中孔范围内的水分含量主要受百年木炭-C含量的影响。这种效果对沙壤土最强。另一方面，百年木炭的存在增加了粉砂壤土的 pF 值在 1.5 和 2 之间的水力传导率，而对于壤质和沙壤土没有观察到木炭的影响。讨论了关于生物炭特性和生物炭颗粒在土壤中分布的各种方式的结果。