Grasslands are a globally important use of land for food and fibre production, which often require the addition of phosphorus (P) fertiliser to maximise plant production. However, a large proportion of the added P can accumulate in pools of poorly available inorganic and organic P in the surface soil layer under grasslands. The aim of this study was to identify the chemical nature of the organic P in soils from a long-term fertiliser by grazing permanent pasture experiment that have received varying additions of phosphatic fertiliser (cumulative P input of 27, 169, 311, 513, 745 and 1035 kg P ha⁻¹) over a period of 37 years. The design of the experiment uniquely provides insight into the response of soil organic P to the addition of fertiliser P on the decadal scale. On average, 46% of the added fertiliser P was recovered as total P in the 0–100 mm soil layer after 37 years of phosphate addition. The content of both inorganic and organic forms of soil P increased with the addition of fertiliser P. The accumulation of organic P increased linearly up to a cumulative P input of 745 kg P ha⁻¹ and plateaued thereafter. The majority of organic P in all treatments was detected as a broad signal in the phosphomonoester region of solution ³¹P nuclear magnetic resonance (NMR) spectra; this also accounted for 79% of the accumulated organic P in fertilised soil. Our results indicate that accumulation of P in the organic portion as complex forms eventually reaches a new equilibrium where no net accumulation would be expected with further addition of phosphate.

中文翻译：

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长期放牧实验中添加磷肥的土壤磷库

草原是全球用于粮食和纤维生产的重要土地，通常需要添加磷（P）肥料以最大化植物产量。但是，大部分添加的P会积聚在草地下表层土壤中难得的无机P和有机P中。这项研究的目的是通过放牧永久性牧草试验来鉴定长期肥料中土壤中有机磷的化学性质，该试验已添加了不同量的磷肥（累计磷输入量为27、169、311、513、745）和1035 kg P ha ^-1），期限为37年。该实验的设计独特地洞察了土壤有机磷对年代际尺度上添加肥料P的响应。添加磷37年后，在0-100 mm土层中平均回收了46％的添加肥料P作为总磷。土壤P的无机形式和有机形式的含量均随着肥料P的添加而增加。有机P的累积量线性增加，直至累积P输入为745 kg P ha ^-1并随后达到稳定。在所有处理中，大多数有机磷在溶液³¹的磷酸单酯区域中被检测为宽信号P核磁共振（NMR）谱；这也占了施肥土壤中有机磷累积的79％。我们的结果表明，有机物中P以复杂形式的积累最终达到了一个新的平衡，在该平衡下，进一步添加磷酸盐不会产生净积累。