Abstract

Fertilization of grassland pastures may be a non-point pollution source in the Azores archipelago, despite the high phosphorus (P) retention of Andosols. To evaluate the risk of P desorption, representative Andosols samples (0–15 cm) were subdivided in five layers and different P pools were measured. The risk of P unloading into waters was assessed by the degree of phosphorus saturation (DPS), and by the P concentration in equilibrium solutions (0.01 M CaCl₂). The higher contents in the superficial layers suggest P accumulation due to pasture overfertilization. The organic P represented about 54% of the total P, with an overall average of 2.66 g P_t/kg. Despite being above the agronomic threshold, the soil with the highest average mean values of extractable inorganic P, 77 mg P_Olsen/kg and and 73.7 mg P_AL/kg, is still below environmental thresholds and none of the soils had DPS values above 25%, which is the critical value associated with eutrophication of surface waters. Similarly, all the P concentrations in the equilibrium CaCl₂ solutions were below the critical limits. Therefore, P desorption from these soils did not seem to be the main process responsible for effective waterbodies eutrophication in the Azores. Since mineral fertilizers are applied superficially, the hypothesis of their direct runoff during rainfall events, even before their complete dissolution and interaction with the soil matrix, must be considered. Consequently, P fertilization with deep-banding systems may be the alternative to the interdiction of fertilizers in the most sensitive and hilly areas of the watersheds.

中文翻译：

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受精牧场下雄甾烷磷素流失的风险。

摘要

尽管Andosols的磷（P）含量高，但在亚速尔群岛中，草地牧场的施肥可能是非点源污染源。为了评估P解吸的风险，将代表性的Andosols样品（0-15 cm）细分为五层，并测量了不同的P池。通过磷饱和度（DPS）和平衡溶液中的P浓度（0.01 M CaCl ₂）评估P释放到水中的风险。表层较高的含量表明，由于牧场过度施肥，磷积累。有机磷约占总磷的54％，平均总磷为2.66 g P _t/公斤。尽管高于农艺阈值，但可提取无机P均值最高的土壤分别为77 mg P _Olsen / kg和73.7 mg P _AL / kg，仍低于环境阈值，并且没有土壤的DPS值高于25 ％，这是与地表水富营养化相关的临界值。同样，平衡CaCl ₂中的所有P浓度解决方案低于关键限制。因此，从这些土壤中解吸磷似乎不是造成亚速尔群岛有效水体富营养化的主要过程。由于矿物肥料是表面施用的，因此即使在其完全溶解和与土壤基质相互作用之前，也必须考虑降雨期间其直接径流的假设。因此，在分水岭最敏感和最丘陵的地区，采用深层系统施肥可能是阻止肥料施肥的替代方法。