Mumbi Rose C K, Williams Mark R, Ford William I, Camberato James J, Penn Chad J
USDA ARS, National Soil Erosion Research Laboratory, West Lafayette, IN 47907, United States of America; Purdue University, Department of Agronomy, West Lafayette, IN 47907, United States of America.
USDA ARS, National Soil Erosion Research Laboratory, West Lafayette, IN 47907, United States of America.
J Contam Hydrol. 2025 Feb;269:104501. doi: 10.1016/j.jconhyd.2025.104501. Epub 2025 Jan 11.
Agricultural phosphorus (P) losses may result from either recently applied fertilizers or from P accumulated in soil and sediment. While both P sources pose an environmental risk to freshwater systems, differentiating between sources is crucial for identifying and implementing management practices to decrease loss. In this study, laboratory rainfall simulations were completed on runoff boxes and undisturbed soil columns before and after fertilizer application. The oxygen-18 signature of phosphate (δO) in fertilizer, surface runoff, subsurface leachate, and soil were analyzed (n = 107 samples) to quantify new (recently applied) and old (soil) P losses in runoff and leachate. Results showed that dissolved reactive P (DRP) concentration in runoff and leachate substantially increased during the rainfall simulation immediately after fertilizer application, with runoff and leachate δO similar to fertilizer δO signatures. Greater than 90 % of the DRP load during this event could be attributed to direct loss of P from fertilizer using δO. Beyond the first rainfall event after fertilizer application, DRP concentration decreased and leachate δO values differed from the fertilizer values. Interpretation of isotope results was challenging because both abiotic (isotope fractionation during transport) and biotic (P cycling) processes may have influenced δO signatures during these subsequent events. While abiotic effects on δO appear more probable given the experimental conditions in the current study (high soil test P concentration, short duration between rainfall simulations, and strong relationship between event water and δO signature), tracing or separating P sources remains highly uncertain during these events post-fertilizer application. Findings highlight both potential opportunities and challenges of using δO to trace sources of P through the landscape.
农业磷（P）流失可能源于近期施用的肥料，也可能源于土壤和沉积物中积累的磷。虽然这两种磷源都会对淡水系统构成环境风险，但区分磷源对于确定和实施减少磷流失的管理措施至关重要。在本研究中，在施肥前后对径流箱和原状土柱进行了实验室降雨模拟。分析了肥料、地表径流、地下渗滤液和土壤中磷酸盐的氧-18特征（δO）（n = 107个样本），以量化径流和渗滤液中新增（近期施用）和旧有（土壤）磷的流失。结果表明，施肥后立即进行降雨模拟时，径流和渗滤液中溶解态活性磷（DRP）浓度大幅增加，径流和渗滤液的δO与肥料的δO特征相似。利用δO可将此次事件中超过90%的DRP负荷归因于肥料中磷的直接流失。施肥后的首次降雨事件之后，DRP浓度下降，渗滤液的δO值与肥料值不同。同位素结果的解释具有挑战性，因为在这些后续事件中，非生物过程（运输过程中的同位素分馏）和生物过程（磷循环）都可能影响δO特征。鉴于本研究的实验条件（土壤有效磷浓度高、降雨模拟之间的持续时间短以及事件水与δO特征之间的强相关性），非生物因素对δO的影响似乎更有可能，但在施肥后的这些事件中，追踪或区分磷源仍然高度不确定。研究结果突出了利用δO追踪景观中磷源的潜在机遇和挑战。
