J Environ Qual. 2019 May;48(3):568-578. doi: 10.2134/jeq2018.07.0285.
The risk of P leaching from topsoil based on the change-point estimated via a split-line model between Olsen P and leachable P extracted by 0.01 M CaCl has been reported. However, little information is available for the assessment of P leaching from soil profiles. In this study, samples were collected at three depth profiles (0-20 cm, topsoil; 20-40 cm, subsoil; 40-60 cm, third-layer soil) at each of 74 sites under agriculture and forest in an agroforestry area. A cascade extraction method was proposed to determine the leachable P in the subsoil, extracted by the topsoil extraction solution; a similar extracted process was followed in the third-layer soil, and in the topsoil, it was still extracted by 0.01 M CaCl. A positive linear correlation was found between the subsoil leachable P extracted by the topsoil extraction solution and the accumulated P obtained from the subsoil leached by topsoil leachates, and so on. Therefore, the cascade extraction method for determining leachable P from topsoils and underlying soils could be valuable for predicting the potential of P leaching from soil profiles. Approximately 81, 73, and 73% of the agricultural sampling sites were at or above the change-points for the soil depths of 0 to 20, 20 to 40, and 40 to 60 cm (30.4, 32.9, and 18.2 mg kg respectively); these values were higher than those for the forest site, implying a high risk of P leaching from agricultural soil profiles in the study area.
已经报道了基于通过折线模型估计的 Olsen P 和 0.01 M CaCl 提取的可提取 P 之间的断点来估算表土中 P 淋溶的风险。然而，对于评估土壤剖面中 P 淋溶的信息很少。在这项研究中，在农林区的 74 个农业和森林点的三个深度剖面（0-20 cm，表土；20-40 cm，底土；40-60 cm，第三层土）中收集了样本。提出了级联提取方法来确定底土中的可提取 P，通过表土提取液提取；在第三层土中遵循类似的提取过程，在表土中仍用 0.01 M CaCl 提取。发现表土提取液提取的底土可提取 P 与通过表土浸提液淋洗的底土获得的累积 P 之间存在正线性相关关系，依此类推。因此，用于确定表土和底土中可提取 P 的级联提取方法对于预测土壤剖面中 P 淋溶的潜力可能是有价值的。大约 81%、73%和 73%的农业采样点位于 0 至 20、20 至 40 和 40 至 60 cm 土壤深度的转折点或以上（分别为 30.4、32.9 和 18.2 mg kg）；这些值高于森林点的值，这意味着研究区农业土壤剖面中 P 淋溶的风险很高。
