Yield increases by use of phosphorus (P) fertiliser has been a defining aspect of last century's agriculture, but in many countries P inputs are now being regulated to avoid ecological damage and improve agricultural sustainability. We tested the hypothesis that P forms and functions in agricultural soils have changed over a period of 50–70 years of agricultural change using topsoils from 35 agricultural sites in North East Scotland compared at ‘original’ and ‘resampled’ timepoints. The original dried and archived samples were collected between 1951 and 1981, and resampling took place in the autumn of 2017 with all samples reanalysed at the same time and by same methods. A range of soil extractants, from labile (water soluble) P, carbon (C) and nitrogen (N) forms, to surface exchangeable P (acid ammonium oxalate extraction), to complexed P (NaOH-EDTA extraction), were compared with agronomic soil test P (modified Morgan; MM-P), soil pH, and, on a subset of five time pairs (n = 10), specific P compounds using ³¹P NMR spectroscopy. Whilst MM-P had declined significantly in time, all soils were originally and remained at high soil P status. In contrast, no change in labile P pools, nor in the more refractory P pools that replenish labile P, were observed. In the subset analysed by NMR, orthophosphate P consistently increased in concentration. This suggests that soil P shows a slow (multidecadal) response to the documented reductions in fertiliser P for the study region. Significantly greater soil pH (by 0.4 units) over time and reduced water-soluble C and N forms suggests that labile P in contemporary soils exists in a biogeochemical environment of enhanced solubility and in excess to other available macronutrients that control its microbial cycling. This study represents a long and important period of changing drivers acting on soil P change with potential to improve understanding future soil P trajectories. The value of archived historical soils samples is shown, if care in interpretation of storage implications is made.

中文翻译：

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苏格兰农业变化时期的土壤磷

通过使用磷 (P) 肥料提高产量一直是上个世纪农业的一个决定性方面，但在许多国家，现在正在对磷投入进行监管，以避免生态破坏和提高农业可持续性。我们使用来自苏格兰东北部 35 个农业地点的表土在“原始”和“重新采样”时间点进行比较，检验了农业土壤中磷的形式和功能在 50-70 年的农业变化期间发生了变化的假设。原始干燥和存档的样品是在 1951 年至 1981 年间收集的，并于 2017 年秋季进行了重新取样，所有样品同时以相同的方法重新分析。一系列土壤提取剂，从不稳定（水溶性）磷、碳 (C) 和氮 (N) 形式，到表面可交换磷（酸性草酸铵提取），n  = 10)，特定的 P 化合物使用³¹P 核磁共振光谱。虽然 MM-P 随时间显着下降，但所有土壤最初并保持在高土壤 P 状态。相比之下，没有观察到不稳定 P 池的变化，也没有观察到补充不稳定 P 的更难处理的 P 池的变化。在 NMR 分析的子集中，正磷酸盐 P 的浓度持续增加。这表明土壤磷对研究区域化肥磷减少的记录显示出缓慢（数十年）响应。随着时间的推移，土壤 pH 值显着升高（0.4 个单位）和水溶性 C 和 N 形式的减少表明，当代土壤中的不稳定 P 存在于溶解度增强的生物地球化学环境中，并且超过控制其微生物循环的其他可用常量营养素。这项研究代表了一个长期而重要的改变驱动因素对土壤磷变化的影响，有可能提高对未来土壤磷轨迹的理解。如果在解释存储影响时小心谨慎，则会显示存档的历史土壤样本的价值。