A legacy of using P fertilizers on grazed pastures has been enhanced soil fertility and an associated increased risk of P loss in runoff. Rainfall simulation has been extensively used to develop relationships between soil test P (STP) and dissolved P (DP) in runoff as part of modeling efforts scrutinizing the impact of legacy P. This review examines the applicability of rainfall simulation to draw inferences related to legacy P. Using available literature, we propose a mixing layer model with chemical transfer to describe DP mobilization from pasture soils where readily available P in the mixing layer is rapidly exhausted and contact time controls DP concentrations responsible for subsequent DP mobilization. That conceptual model was shown to be consistent with field monitoring data and then used to assess the likely effect of rainfall simulation protocols on DP mobilization, highlighting the influence of soil preparation, scale and measurement duration, and, most important, hydrology that can facilitate the physical transport of P into and out of surface flow. We conclude that rainfall simulation experimental protocols can have severe limitations for developing relationships between DP in runoff and STP that are subsequently used to estimate legacy P contributions to downstream water resources.

中文翻译：

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估算牧场遗留来源的溶解磷损失：土壤测试和小规模降雨模拟器的局限性

在放牧的牧场上使用磷肥的遗留问题是提高了土壤肥力，并增加了径流中磷流失的风险。降雨模拟已被广泛用于开发径流中土壤测试 P (STP) 和溶解 P (DP) 之间的关系，作为审查遗留 P 影响的建模工作的一部分。这篇评论检查了降雨模拟的适用性，以得出与遗留 P 相关的推论P. 使用现有文献，我们提出了一个带有化学转移的混合层模型来描述牧场土壤中的 DP 动员，其中混合层中容易获得的 P 迅速耗尽，接触时间控制负责后续 DP 动员的 DP 浓度。该概念模型被证明与现场监测数据一致，然后用于评估降雨模拟协议对 DP 动员的可能影响，突出土壤准备、规模和测量持续时间的影响，最重要的是，可以促进水文P 进入和离开表面流的物理传输。我们得出结论，降雨模拟实验协议对于开发径流中的 DP 和 STP 之间的关系可能有严重的限制，这些关系随后用于估计对下游水资源的遗留 P 贡献。