Spatial variability of physical attributes and soil aggregates in archaeological dark dirt under pasture

Abstract Some areas of archaeological dark dirt in the Amazon have been used with pasture that has generated great concern regarding changes in soil physical attributes and its aggregation state. The objective of this study was to evaluate the spatial variability and possible modifications of soil physical and aggregate attributes in archaeological black dirt under pasture. A grid of 80 x 56m with 88 sampling points distributed in 8 x 8m were marked. Soil layers at 0-0.05, 0.05-0.10, and 0.10-0.20m were analyzed for: soil density (SD), total organic carbon (TOC), carbon stock (C stock), meanweight diameter (MWD), macroporosity (Macro), microporosity (Micro), and total porosity (TP). From semivariograms tests it was verified the occurrence of spatial dependence. Even with major pasture cover in the study area it was observed that the values of Ds, Macro, and VTP were above or below the reference values, which may cause restriction for root growth of plants and water infiltration in the soil. The DMP and Ds were COT-dependent because values of both increase or decrease depending on the soil layer. When higher the soil layer there was an increase in carbon stock.

摘要 亚马逊区域的部分考古黑土（archaeological dark dirt）地块被用于牧场经营，由此引发学界对其土壤物理属性及团聚体状态发生改变的广泛担忧。本研究旨在评估牧场覆盖下考古黑土的空间变异性，以及土壤物理与团聚体属性可能出现的变化。研究划定了一块80×56m的样地，以8×8m为网格间距设置了88个采样点。对0~0.05m、0.05~0.10m及0.10~0.20m三层土壤开展了以下指标检测：土壤容重（SD）、总有机碳（TOC）、碳储量（C stock）、平均重量直径（MWD）、大孔隙度（Macro）、微孔隙度（Micro）及总孔隙度（TP）。通过半方差函数（semivariograms）检验，证实了空间依赖性的存在。尽管研究区域以牧场植被为主要覆盖物，但仍观测到土壤容重、大孔隙度及总孔隙度的数值偏离了参考范围，这可能会限制植物根系生长与土壤水分入渗。平均重量直径与土壤容重与总有机碳存在相关性，二者的数值随土层深度发生升降变化。土层越深，碳储量越高。