Abstract Boron is an essential micronutrient for plants, but can also be toxic when present in excess in the soil solution. A multi-surface geochemical model was used to assess the important processes that affect the distribution of the geochemically reactive B in soils over the solution and solid phase. The multi-surface model was based on the adsorption of B on dissolved and solid humic acids, representing reactive organic matter, ferrihydrite, representing the Fe and Al (hydr)oxides, and clay mineral edges. In addition, the performance of previously proposed extraction methods for measuring reactive B was evaluated. Based on B measured in 0.01 M CaCl2 soil extracts (7-85 μmol kg-1 soil), we calculated the reactive boron concentration for 5 temperate and 5 tropical soils (8-106 μmol kg-1 soil). We found that extractions with 0.43 M HNO3 or with 0.2 M mannitol + 0.1 M triethanolamine buffer extract on average 240 and 177 % of the reactive B predicted by the model, thus releasing additional B that is assumed to be not or only very slowly available for exchange with the soil solution. Reactive B calculated by the model corresponded best to the B measured in a 0.05 M KH2PO4 (pH 4.5) extraction. In general, the multi-surface modeling showed that 68 % or more of reactive boron was present in the solution phase for the soils in this study and that the adsorption was dominated by oxides in the tropical soils, while solid organic matter was the main adsorbent in the temperate soils. When changing the soil pH(CaCl2), B concentration was found to decrease with increasing pH, and both experimental data and modelling suggests that this effect is mainly due to increased binding of B to organic matter.

中文翻译：

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温带和热带土壤中硼的形态和可提取性：多表面建模方法

摘要 硼是植物必需的微量营养素，但在土壤溶液中过量存在时也会产生毒性。使用多表面地球化学模型来评估影响地球化学反应性 B 在土壤中溶液和固相分布的重要过程。多表面模型基于 B 在溶解和固体腐殖酸上的吸附，代表活性有机物，水铁矿，代表 Fe 和 Al（氢）氧化物，以及粘土矿物边缘。此外，评估了先前提出的用于测量活性 B 的提取方法的性能。基于在 0.01 M CaCl2 土壤提取物（7-85 μmol kg-1 土壤）中测量的 B，我们计算了 5 种温带和 5 种热带土壤（8-106 μmol kg-1 土壤）的活性硼浓度。我们发现提取为 0。43 M HNO3 或 0.2 M 甘露醇 + 0.1 M 三乙醇胺缓冲液提取物平均为模型预测的反应性 B 的 240% 和 177%，从而释放额外的 B，该 B 被认为不能或仅非常缓慢地可用于与土壤溶液交换. 由模型计算的反应性 B 与在 0.05 M KH2PO4 (pH 4.5) 萃取中测量的 B 最相符。总的来说，多表面模型表明，本研究中土壤的溶液相中存在 68% 或更多的活性硼，并且热带土壤中的吸附以氧化物为主，而固体有机物是主要的吸附剂。在温带土壤中。当改变土壤 pH（CaCl2）时，发现 B 浓度随着 pH 的增加而降低，