Less than 40% of phosphate fertilizer applied to soils is typically taken up by the intended crop within the year of application because of strong soil retention. AVAIL polymers are fertilizer additives that were commercially developed to enhance availability of fertilizer phosphate. Knowledge of underlying mechanisms of phosphate solubilization would help to optimize the effectiveness of these polymers for different soils. This study compared different types and levels of AVAIL polymers in solubilizing (ad)sorbed and precipitated phosphate to gain insights into the mechanisms involved. Varying inputs of four newer forms of polymers and the original AVAIL (Original) were co‐reacted with one level of phosphate (ad)sorbed on ferrihydrite or noncrystalline Al hydroxide in batch (ad)sorption experiments or with Fe and Ca phosphate precipitates in dissolution experiments. Dissolved phosphate increased with increasing levels of co‐added polymers reacted with (ad)sorbents or phosphate precipitates. Across input levels evaluated, the Original AVAIL generally solubilized more phosphate from ferrihydrite than any of the new formulations. The Original and the new Liquid 2 formulation equally solubilized the greatest phosphate from Fe phosphate, whereas Liquid 2 solubilized more phosphate from Al hydroxide and Ca phosphate. (Ad)sorption and dissolution results implied competitive (ad)sorption and complexometric dissolution as key mechanisms. Our results suggest that the effectiveness of AVAIL polymers in soils depends on the level of added polymer charge relative to phosphate adsorption capacities or the types of phosphate minerals present.

中文翻译：

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通过不同的AVAIL聚合物从吸附剂和沉淀物中溶解磷酸盐

由于土壤保持力强，在施用的一年内，预定作物通常只吸收不到40％的磷肥。AVAIL聚合物是工业上开发的肥料添加剂，可提高磷酸盐肥料的利用率。磷酸盐增溶的潜在机理的知识将有助于优化这些聚合物对不同土壤的有效性。这项研究比较了不同类型和含量的AVAIL聚合物在增溶（吸附）和沉淀的磷酸盐中的作用，以深入了解所涉及的机理。在批次（吸附）吸附实验中，将四种新形式的聚合物和原始的AVAIL（原始）的各种输入与一级吸附在亚铁酸盐或非晶态氢氧化铝上的磷酸盐（吸附）或溶解时的Fe和Ca磷酸盐沉淀共反应实验。溶解的磷酸盐随着与（吸附剂）吸附剂或磷酸盐沉淀物反应的共添加聚合物含量的增加而增加。在评估的输入水平上，原始AVAIL通常比任何新配方都可溶解更多的水铁矿磷酸盐。原始液2和新液2均能从磷酸铁中溶解最大的磷酸盐，而液2从氢氧化铝和磷酸钙中溶解更多的磷酸盐。（Ad）吸附和溶解结果暗示竞争性（ad）吸附和络合溶解是关键机制。