Biochar is recommended as a soil amendment for its positive influence on soil hydrological properties, which results in improved soil fertility and crop yield. Much research in the last decade has been conducted in field and laboratory conditions on the effect of biochar on the hydraulic properties of soil. However, reported results in the literature are substantially inconsistent. Here we performed a meta-analysis to capture the variations in change in hydraulic properties of arable soils after application of different rates of biochar. The meta-analysis revealed that high biochar rates (>50 t ha⁻¹) compared to low rates (<20 t ha⁻¹) significantly improved dry bulk density in sandy and clay soils, in field and laboratory experiments. However, field capacity only improved in laboratory experiments on sandy soils. The plant available water, permanent wilting point and saturated hydraulic conductivity did not significantly increase at high rates of biochar application compared to the low rates when applied to different types of soils in both field and laboratory experiments. We discuss possible reasons for this, including hydrophobicity of the biochar with future research directions. We concluded that the current evidence does not support the notion that the application of biochar improves soils' available water capacity.

中文翻译：

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更大，但不一定更好：生物炭对土壤水力特性的影响

生物炭因其对土壤水文特性的积极影响而被推荐作为土壤改良剂，从而提高土壤肥力和作物产量。在过去十年中，在野外和实验室条件下对生物炭对土壤水力特性的影响进行了大量研究。然而，文献中报道的结果基本上不一致。在这里，我们进行了荟萃分析，以捕捉施用不同比例的生物炭后耕地土壤水力特性变化的变化。荟萃分析显示，高生物炭率（>50 t ha ^-1）与低生物炭率（<20 t ha ^-1) 在田间和实验室实验中显着提高了沙质和粘土土壤的干容重。然而，田间持水量仅在沙质土壤的实验室试验中得到提高。在田间和实验室实验中，与应用于不同类型土壤时的低速率相比，在高速率生物炭施用下，植物可用水、永久枯萎点和饱和导水率没有显着增加。我们讨论了可能的原因，包括 biochar 的疏水性以及未来的研究方向。我们得出的结论是，目前的证据不支持应用生物炭提高土壤可用水容量的观点。