Soil dataset from poplar cultivation sites in northern Italy plains

The soil sampling activities conducted in the plains of northern Italy adhered to the methodology outlined in the poplar inventory dataset by Rizza et al. (2023). The dataset consisted of 2,322 clusters that were georeferenced on a three-kilometre UTM grid, systematically distributed across an area spanning 4,179,600 hectares. Each cluster comprised nine subunits aligned with the points on a 500-meter square grid. The soil sampling took place between 1994 and 1996 and focused on locations with poplar plantations that were at least five years old in 1994. To obtain the samples, a pedological profile was manually excavated, and each layer was identified. One kilogram of soil was collected from each layer. Each soil sample was labelled with the region's sampling letter, cluster number, and element number. A maximum of five depths were examined for each sample. The texture characteristics (fine sand, coarse sand, fine silt, coarse silt, and clay) and certain chemical properties (limited to the first horizon) were documented, including NH4+, NO3-, CaCO3, P2O5, pH, organic matter, and soil carbon. Moreover, the presence of irrigation was recorded, and for the first layer, the depth of the temporary and permanent water table was reported. It is important to note that for certain samples, only the surface soil layers were evaluated, omitting depths exceeding 60 centimetres. Additionally, the soil samples were air dried, sieved to two millimetres and then scanned using an ASD Fieldspec instrument, particularly the LabSpec Pro Spectrophotometer LSP 350-2500P Analytical Spectral Devices, Inc. The reflectance at wavelength range 350–2500 nm was acquired with an interval of 1 nm. The resulting Vis-Nir soil spectral library was integrated with the soil data and entered in two excel worksheets joined by a sampleID.本次在意大利北部平原开展的土壤采样活动，严格遵循Rizza等人2023年发布的杨树清查数据集（poplar inventory dataset）所规定的方法学流程。该数据集包含2322个地理配准至3公里通用横轴墨卡托（Universal Transverse Mercator, UTM）网格的采样簇，系统分布于总面积达4179600公顷的研究区域内。每个采样簇包含9个亚单元，这些亚单元与500米方格网格上的点位一一对应。土壤采样工作于1994年至1996年间实施，采样目标为1994年时树龄至少5年的杨树人工林分布区域。为获取土壤样品，研究人员手动挖掘土壤剖面并完成各土层的识别与划分，从每一层土层中采集1千克土壤样品。每份土壤样品均通过采样区域字母、簇编号以及元素编号进行唯一标识。每份样品最多可开展5个土层深度的检测分析。研究记录了土壤的质地特征（细砂、粗砂、细粉粒、粗粉粒及黏土）以及部分化学性质（仅针对第一层土层），包括NH₄⁺、NO₃⁻、CaCO₃、P₂O₅、pH值、有机质及土壤有机碳。此外，研究还记录了采样区域的灌溉条件存在情况，并针对第一层土层，报告了暂时性与永久性地下水位的埋深。需要特别说明的是，部分样品仅对表层土壤进行了检测，未采集深度超过60厘米的土层样品。另外，所有土壤样品均经过风干处理、过2毫米筛筛分后，使用ASD FieldSpec仪器（具体为LabSpec Pro分光光度计LSP 350-2500P，Analytical Spectral Devices, Inc.出品）进行光谱扫描，采集了350~2500 nm波长范围内的土壤反射光谱数据，光谱采样间隔为1 nm。最终得到的可见光-近红外（Vis-NIR）土壤光谱库与土壤理化数据集完成整合，并通过sampleID关联至两个Excel工作表中。