Polyphosphate fertilizer is an alternative to traditional orthophosphate fertilizer, but it is unclear whether it provides greater soil phosphorus (P) mobility and availability than orthophosphate fertilizer. This study aimed to examine the chemical behaviour of polyphosphate after its application to the soil. The hydrolysis, sorption, and P transformation of two types of polyphosphate fertilizers (short-chain and long-chain) were examined for two types of soils (acidic Acrisol and calcareous Cambisol), with orthophosphate serving as the control treatment. ³¹P NMR spectroscopic analyses indicated that polyphosphate in soil was rapidly converted to pyrophosphate, which was then hydrolyzed to orthophosphate at a slower rate. In general, in the calcareous Cambisol, the addition of short-chain polyphosphate fertilizer resulted in greater soil P mobility as measured by greater soil pore water orthophosphate concentration than the control. Thus, short-chain polyphosphate fertilizer tended to be more effective than orthophosphate in calcareous soils. This was in contrast to the result of an aqueous incubation experiment, in which a lower pH increased the rate of polyphosphate hydrolysis. Indeed, in both soils, the sorption of total P was greater when P was added as polyphosphate than when it was added as orthophosphate. Moreover, polyphosphate sorption appeared to be mainly controlled by soil iron and aluminium minerals, because the Acrisol showed stronger polyphosphate sorption than the Cambisol due to its greater amorphous iron content. It appears that polyphosphate was first adsorbed on soil minerals before being hydrolyzed to release orthophosphate, and calcium may have played an important role in the hydrolysis of polyphosphate as evidenced by the greater P release in calcareous Cambisol. Our results suggest that soil characteristics, such as acidity, iron, aluminium, and calcium content, should be considered when evaluating the P efficiency of polyphosphate fertilizers.

中文翻译：

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聚磷酸盐在两种不同土壤中的水解、吸附和转化

聚磷酸盐肥料是传统正磷酸盐肥料的替代品，但尚不清楚它是否比正磷酸盐肥料提供更大的土壤磷 (P) 流动性和可用性。本研究旨在研究聚磷酸盐施用于土壤后的化学行为。研究了两种类型的土壤（酸性 Acrisol 和钙质 Cambisol）的两种聚磷酸盐肥料（短链和长链）的水解、吸附和磷转化，正磷酸盐作为对照处理。³¹P NMR 光谱分析表明，土壤中的聚磷酸盐迅速转化为焦磷酸盐，然后以较慢的速率水解为正磷酸盐。一般来说，在钙质 Cambisol 中，添加短链聚磷酸盐肥料会导致土壤磷迁移率更高，这是通过比对照更高的土壤孔隙水正磷酸盐浓度来衡量的。因此，在钙质土壤中，短链聚磷酸盐肥料往往比正磷酸盐肥料更有效。这与水性培养实验的结果形成对比，在水性培养实验中，较低的 pH 值会增加聚磷酸盐的水解速率。事实上，在这两种土壤中，当 P 以聚磷酸盐形式添加时，总 P 的吸附量大于以正磷酸盐形式添加时。而且，聚磷酸盐的吸附似乎主要受土壤铁和铝矿物质的控制，因为 Acrisol 显示出比 Cambisol 更强的聚磷酸盐吸附，因为它的无定形铁含量更高。似乎聚磷酸盐在水解释放正磷酸盐之前首先吸附在土壤矿物质上，钙可能在聚磷酸盐的水解中发挥了重要作用，钙质 Cambisol 中更多的 P 释放证明了这一点。我们的结果表明，在评估聚磷酸盐肥料的磷效率时，应考虑土壤特性，例如酸度、铁、铝和钙含量。似乎聚磷酸盐在水解释放正磷酸盐之前首先吸附在土壤矿物质上，钙可能在聚磷酸盐的水解中发挥了重要作用，钙质 Cambisol 中更多的 P 释放证明了这一点。我们的结果表明，在评估聚磷酸盐肥料的磷效率时，应考虑土壤特性，例如酸度、铁、铝和钙含量。似乎聚磷酸盐在水解释放正磷酸盐之前首先吸附在土壤矿物质上，钙可能在聚磷酸盐的水解中发挥了重要作用，钙质 Cambisol 中更多的 P 释放证明了这一点。我们的结果表明，在评估聚磷酸盐肥料的磷效率时，应考虑土壤特性，例如酸度、铁、铝和钙含量。