Depth profile of plant nutrients and acidity in a non-allophanic Andosol as affected by a half-century of fertilization

To clarify the effects of long-term fertilization on the depth profile of plant nutrients and soil acidity in non-allophanic Andosols, a soil survey was conducted on fertilized grassland and adjacent secondary forest in Kuju highland, Oita Prefecture, Japan. Both of the experimental plots had been managed as a semi-natural grassland (managed by cutting, mowing, and burning for raising cows) before mid of the 1960s, and then, the former had been converted into reclaimed grassland with applying agricultural materials such as fertilizers, manure, and lime, and the latter had been abandoned which resulted in secondary succession into the secondary forest. The comparison of the depth profiles between the two plots revealed that the applied Ca2+ and Mg2+ reached at least 100 cm depth of the non-allophanic Andosol profile. The soil pH was increased at least at the depth of 100 cm, and the plant-toxic level of soil acidity (≥12 mmol kg−1), which is one of the characteristic properties of non-allophanic Andosols, was decreased in the fertilized grassland soil. Soil available P was also observed to be increased at least 80 to 100 cm depth, although the mobility was smaller than those of exchangeable cations and soil acidity. Other soil chemical properties, such as cation exchange capacity, total C and N contents, pyrophosphate-extractable Al (Alp) and Fe (Fep), acid-oxalate-extractable Al (Alo), Fe (Feo), and Si (Sio), Alp/Alo ratio, and Alo + 1/2 Feo, were not significantly altered by the modern grassland management activities. This study reveals considerable loss of plant nutrients from the fertilized grassland soil of a non-allophanic Andosol during a half-century. The loss of plant nutrients should be reduced for sustainable agriculture and conserving the natural environment.为阐明长期施肥对非非晶质火山灰土（non-allophanic Andosols）中植物养分深度分布及土壤酸度的影响，研究团队在日本大分县久住高原的施肥草地与邻近次生林开展了土壤调查。两处试验样地在20世纪60年代中期前均作为半天然草地进行管理（通过刈割、割草及焚烧方式饲养肉牛）；其后，其中一处被改造为施用化肥、厩肥与石灰等农用物资的人工改良草地，另一处则被弃耕，经次生演替形成次生林。对两处样地土壤深度剖面的对比分析显示，施入的钙离子（Ca²+）与镁离子（Mg²+）可渗透至非非晶质火山灰土剖面至少100厘米深度处。施肥草地土壤的pH值至少在100厘米深度处有所升高，且作为非非晶质火山灰土典型特征之一的具植物毒性的土壤酸度水平（≥12 mmol·kg⁻¹）显著降低。土壤有效磷含量同样在至少80至100厘米深度处有所提升，尽管其迁移能力弱于交换性阳离子与土壤酸度。其余土壤化学性质，如阳离子交换量、总碳与总氮含量、焦磷酸盐浸提态铝（Alp）与铁（Fep）、酸性草酸浸提态铝（Alo）、铁（Feo）与硅（Sio）、Alp/Alo比值以及Alo + 1/2 Feo，均未因现代草地管理活动发生显著变化。本研究揭示，半个世纪以来，非非晶质火山灰土的施肥草地土壤发生了大量植物养分流失。为实现农业可持续发展与自然环境保护，需采取措施减少植物养分流失。