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

土壤木炭已被证明在土壤养分动态中发挥关键作用[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。尤其缺乏数据和概念框架来解释观察到的木炭对土壤水文特性的改变。了解木炭对土壤的影响越来越重要，因为人类正在无意或有意地改变土壤中的木炭含量，首先是由火灾管理实践和土地利用变化驱动的，其次是通过有意地用木炭修正土壤以提高作物性能和固碳。我们假设木炭通过改变土壤粒度、电荷密度和疏水性来影响土壤水文特性。我们预测，颗粒大小将改变机械相互作用（如孔径、弯曲度），而电荷密度将改变物理化学相互作用，如冲击强度、土壤水势和流动途径。疏水性是表面化学和表面积的函数（部分由晶粒尺寸和孔隙度控制），并会随着这些性质的变化而变化。随着原位风化，木炭颗粒尺寸减小，表面电荷密度增加，因此随着时间的推移，木炭的影响会发生显著变化，因为木炭被纳入土壤粘土部分，而木炭风化过程中无机物质的释放会改变土壤粘土部分。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。我们用混合了木炭的天然土壤和实验室土壤进行实验，测量(1)土壤疏水性，(2)土壤和木炭的表面和体积化学，(3)饱和渗透率，(4)土壤水势，(5)土壤抗拉强度。我们的最终目标是建立一个土壤-炭-水系统的概念模型。

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.