The Effect of Charcoal on Soil Hydrologic Properties Under Natural and Elevated Concentrations

土壤木炭已被证明在土壤中养分的动态中起关键作用[例如Liang等人，2006]，但我们对木炭对土壤物理和化学性质的影响的了解相当有限。 特别是缺乏数据和概念框架来解释观察到的土壤水文特性的木炭改变。 了解木炭对土壤的影响越来越重要，因为人类正在无意和有意地改变土壤中的木炭含量，第一种是由火灾管理实践和土地利用变化驱动的，第二种是故意用木炭改良土壤以提高作物性能和固碳。 我们假设，木炭影响土壤水文性质，通过改变土壤颗粒大小，电荷密度和疏水性。 我们预测，晶粒尺寸将改变机械相互作用（例如，孔径、弯曲度），而电荷密度将改变影响强度、土壤水势和流动路径的物理化学相互作用。 疏水性是表面化学和表面积的函数（部分由粒度和孔隙度控制），并将随这些性质的变化而变化。 随着原位风化，木炭粒度减小，表面电荷密度增加，因此随着木炭被掺入土壤粘粒部分，其本身可以通过木炭风化过程中释放的无机物质而改变，其影响将随时间显著变化。我们正在进行一系列实验，旨在确定木炭影响土壤水文相关物理和化学性质的机制。 我们正在进行实验与天然和实验室土壤与木炭混合，测量（1）土壤疏水性，（2）土壤和木炭的表面和整体化学，（3）饱和渗透性，（4）土壤水势，（5）土壤抗拉强度。 我们的最终目标是开发一个概念模型的土壤-木炭-水系统。

Soil charcoal has been shown to play a key role in the dynamics of nutrients in soils [e.g. Liang et al., 2006], but our understanding of the effects of charcoal on soil physical and chemical properties is quite limited. Particularly absent are both data and a conceptual framework to explain observed charcoal alteration of soil hydrologic properties. Understanding the effects of charcoal on soil is increasingly important because humans are changing soil charcoal content both unintentionally and intentionally, the first driven by fire management practices and land use change, and the second by intentional amendment of soil with charcoal to improve crop performance and sequester carbon. We hypothesize that charcoal affects soil hydrologic properties through alteration of soil grain size, charge density, and hydrophobicity. We predict that grain size will change mechanical interactions (e.g., pore size, tortuosity), while charge density will change physico-chemical interactions which impact strength, soil water potential, and flow pathways. Hydrophobicity is a function of both surface chemistry and surface area (controlled partly by grain size and porosity), and will respond with changes in these properties. Charcoal grain size decreases and surface charge density increases with in situ weathering so the impacts will be vary significantly with time as charcoal is incorporated into the soil clay fraction, which itself can be altered by the release of inorganic materials during charcoal weathering. We are conducting a series of experiments designed to determine the mechanisms through which charcoal affects hydrologically-relevant physical and chemical properties of soils. We are performing experiments with natural and laboratory soils mixed with charcoal, measuring (1) soil hydrophobicity, (2) surface and bulk chemistry of soils and charcoals, (3) saturated permeability, (4) soil water potential, and (5) soil tensile strength. Our ultimate goal is to develop a conceptual model of the soil-charcoal-water system.