Applying phosphorus (P)-rich wastewater to land can significantly enrich P in topsoil and consequently increase the risk of P losses in surface runoff and leaching. We collected 654 samples (0–7.5, 7.5–15, and 15–30 cm depths) of wastewater-irrigated and non-irrigated soils at seven sites across New Zealand to assess the potential P mobility in irrigated soils. The risk of P loss to surface runoff was tested by water extractable P (WEP) whereas the risk of P loss by leaching was tested by calcium chloride extractable P (CaCl₂–P). These environmental P tests are rarely analysed; hence, a published relationship was used to determine if the risk of P losses could be predicted using anion storage capacity (ASC) and Olsen P, two agronomic tests used in New Zealand. The magnitude of WEP and CaCl₂-P could be predicted using the published relationship, but only in non-irrigated soils. Additionally, the mixed model analysis that compared soils and irrigated treatments showed that wastewater-irrigated soils had a greater pH, WEP and CaCl₂–P concentration to 30 cm depth. However, in both irrigated and non-irrigated soils a change point or threshold in ASC was found that could be used to show an increased likelihood of enhanced P leaching (as CaCl₂–P) to deeper layers. In addition, the WEP and CaCl₂-P thresholds, can be used to signal the need for management changes to decrease the risk of P losses to surface water and groundwater.

将富含磷 (P) 的废水施用于土地可以显着富集表土中的磷，从而增加地表径流和浸出中磷损失的风险。我们在新西兰的七个地点收集了废水灌溉和非灌溉土壤的 654 个样本（0-7.5、7.5-15 和 15-30 厘米深度），以评估灌溉土壤中潜在的磷迁移率。P 损失到地表径流的风险通过水可提取 P (WEP) 测试，而浸出 P 损失的风险通过氯化钙可提取 P (CaCl ₂ -P) 测试。这些环境 P 测试很少被分析；因此，使用已发表的关系来确定是否可以使用阴离子存储容量 (ASC) 和 Olsen P（新西兰使用的两项农艺测试）来预测 P 损失的风险。WEP 和 CaCl ₂的量级-P 可以使用已发布的关系进行预测，但仅限于非灌溉土壤。此外，比较土壤和灌溉处理的混合模型分析表明，废水灌溉的土壤在30 厘米深度具有更高的 pH、WEP 和 CaCl ₂ -P 浓度。然而，在灌溉和非灌溉土壤中，发现 ASC 中的一个变化点或阈值可用于显示增强的 P 浸出（如 CaCl ₂ -P）到更深层的可能性增加。此外，WEP 和 CaCl ₂ -P 阈值可用于表明需要改变管理以降低 P 流失到地表水和地下水的风险。