Andersson Helena, Bergström Lars, Ulén Barbro, Djodjic Faruk, Kirchmann Holger
J Environ Qual. 2015 Mar;44(2):535-44. doi: 10.2134/jeq2014.04.0186.
The importance of subsoil features for phosphorus (P) leaching is frequently mentioned, but subsoil effects are still poorly documented. This study examined whether the subsoil of four agricultural Swedish soils (two sand and two clay) functioned as a source or sink for P leaching by measuring P leaching from intact soil columns with topsoil (1.05 m deep) and without topsoil (0.77 m deep) over 3 yr. One sandy soil with high topsoil P content (Olsen P, 84 mg kg) and high subsoil sorption capacity (P sorption index [PSI], 3.7 mmol kg) had low leaching of dissolved reactive P (DRP) from full-length and subsoil lysimeters (0.12 and 0.08 kg ha yr, respectively). The other sandy soil, with high Olsen P content in the topsoil and subsoil (27 and 19 mg kg, respectively) and low PSI in the subsoil (1.4 mmol kg), had high DRP leaching from full-length and subsoil lysimeters (3.33 and 3.29 kg ha yr, respectively). High P content at depth (Olsen P, 21 mg kg) in one clay soil resulted in relatively higher subsoil DRP contribution (89%) to total leaching than observed in the other clay soil (71%). These results indicate that the subsoil can act as source or sink for P leaching, depending on P content, degree of P saturation, and P sorption capacity, and therefore subsoil properties should be considered when selecting mitigation measures to reduce P leaching.
底土特性对磷（P）淋失的重要性常被提及，但底土的影响仍缺乏充分记录。本研究通过测量完整土柱（深1.05米，含表土）和无表土土柱（深0.77米）在3年期间的磷淋失情况，研究了瑞典四种农业土壤（两种砂土和两种黏土）的底土是作为磷淋失的源还是汇。一种表土磷含量高（ Olsen磷，84毫克/千克）且底土吸附能力强（磷吸附指数[PSI]，3.7毫摩尔/千克）的砂土，全长和底土渗漏计中溶解态活性磷（DRP）的淋失量较低（分别为0.12和0.08千克/公顷·年）。另一种砂土，表土和底土的 Olsen磷含量都高（分别为27和19毫克/千克），底土的PSI低（1.4毫摩尔/千克），全长和底土渗漏计中DRP的淋失量高（分别为3.33和3.29千克/公顷·年）。一种黏土中深层的高磷含量（ Olsen磷，21毫克/千克）导致底土DRP对总淋失的贡献相对较高（89%），高于另一种黏土（71%）。这些结果表明，底土可作为磷淋失的源或汇，这取决于磷含量、磷饱和度和磷吸附能力，因此在选择减少磷淋失的缓解措施时应考虑底土特性。
