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.本次在意大利北部平原开展的土壤采样工作，严格遵循了Rizza等人2023年发布的杨树调查数据集（poplar inventory dataset）中规定的方法流程。本数据集共包含2322个采样簇，所有采样簇均基于3公里步长的通用横轴墨卡托（UTM）格网进行地理配准，系统布设覆盖总面积达4179600公顷的区域。每个采样簇包含9个采样单元，各单元与500米正方形格网的节点一一对应。土壤采样工作于1994年至1996年间开展，采样对象为1994年时树龄至少5年的杨树人工林区域。采样过程中，研究人员人工开挖土壤剖面并逐层识别，随后从每一层土壤中采集1千克样品。每份土壤样品均以采样区域字母、采样簇编号及单元编号进行标识。每份样品最多测定5个土层深度的指标。本数据集记录了土壤质地特征（细砂、粗砂、细粉砂、粗粉砂及黏土）以及部分化学性质（仅针对第一层土层），包括铵态氮（NH4+）、硝态氮（NO3-）、碳酸钙（CaCO3）、五氧化二磷（P2O5）、pH值、有机质及土壤有机碳。此外，数据集还记录了采样点的灌溉情况，并针对第一层土层报告了临时地下水位与永久地下水位的埋深。需特别说明的是，部分样品仅测定了表层土壤，未采集深度超过60厘米的土层样本。