Quantifying Uncertainties in Sequential Chemical Extraction of Soil Phosphorus Using XANES Spectroscopy
Quantifying Uncertainties in Sequential Chemical Extraction of Soil Phosphorus Using XANES Spectroscopy
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DOI：
10.1021/acs.est.9b05278
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发表时间：
2020-02-18
影响因子：
11.4
通讯作者：
Zhu, Mengqiang
中科院分区：
文献类型：
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作者：
Gu, Chunhao;Dam, Than;Zhu, Mengqiang
连续化学提取已被广泛应用于土壤磷动态研究和养分管理，但其将磷分配到具有生物意义的池中的效果尚不清楚。在这里，我们使用P-K边缘X射线吸收近边缘结构(XANES)光谱对改进的Hedley提取方案的准确性进行了评估，这些样品具有不同的土壤发育程度导致的不同化学和矿物学性质的9个无碳酸盐土壤样品。对于大多数样品，提取显著高估了钙结合磷(Ca-P，由1M HCl提取)的池大小，这是由于(1)在碱性提取(0.5M NaHCO3，然后0.1M NaOH)过程中P的重新分配，通过NaOH解吸的磷酸盐和可交换的Ca+之间形成新的Ca-P，和/或(2)用1M HCl溶解结晶不良的Fe和Al氧化物，将被这些氧化物遮挡的P释放到溶液中。无论是否存在CaCO3，第一种机制可能发生在富含结晶良好的矿物和可交换的钙离子的土壤中，而第二种机制可能发生在富含结晶较差的铁和铝矿物的土壤中。Ca-P的高估同时也导致了对碱性溶液提取的库的低估。我们的发现确定了显著影响提取的关键土壤参数，这将加强我们使用这一广泛接受的程序对土壤磷动态的理解。
Sequential chemical extraction has been widely used to study soil phosphorus (P) dynamics and inform nutrient management, but its efficacy for assigning P into biologically meaningful pools remains unknown. Here, we evaluated the accuracy of the modified Hedley extraction scheme using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy for nine carbonate-free soil samples with diverse chemical and mineralogical properties resulting from different degrees of soil development. For most samples, the extraction markedly overestimated the pool size of calcium-bound P (Ca-P, extracted by 1 M HCl) due to (1) P redistribution during the alkaline extractions (0.5 M NaHCO3 and then 0.1 M NaOH), creating new Ca-P via formation of Ca phosphates between NaOH-desorbed phosphate and exchangeable Ca2+ and/or (2) dissolution of poorly crystalline Fe and Al oxides by 1 M HCl, releasing P occluded by these oxides into solution. The first mechanism may occur in soils rich in well-crystallized minerals and exchangeable Ca2+ regardless of the presence or absence of CaCO3, whereas the second mechanism likely operates in soils rich in poorly crystalline Fe and Al minerals. The overestimation of Ca-P simultaneously caused underestimation of the pools extracted by the alkaline solutions. Our findings identify key edaphic parameters that remarkably influenced the extractions, which will strengthen our understanding of soil P dynamics using this widely accepted procedure.