Consistency of the Threshold Phosphorus Saturation Ratio across a Wide Geographic Range of Acid Soils

• Published in: Agrosystems, geosciences & environment geosciences & environment, 2018-12, Vol.1 (1), p.1-8
• Main Authors: Dari, Biswanath, Nair, Vimala D., Sharpley, Andrew N., Kleinman, Peter, Franklin, Dorcas, Harris, Willie G.
• Format: Article
• Language: English
• Subjects: Acidic soils; Coastal plains; Consistency; Education; Eutrophication; Fertilizer application; Fertilizers; Iron; Leaching; Mathematical analysis; Phosphorus; Physiographic provinces; Runoff; Saturated soils; Soil testing; Soil water storage; Soils; Storage capacity; Water chemistry; Water quality; Watershed management; Watersheds
• ISSN: 2639-6696; 2639-6696
• DOI: 10.2134/age2018.08.0028

Core Ideas Establish a common threshold in P saturation across a geographic diversity of soils. Predict water‐soluble P from soil P storage capacity to guide fertilizer strategies. Relate runoff P concentration with soil P storage capacity. Loss of legacy soil phosphorus (P) due to historical over‐application of fertilizers and manures can result in eutrophication of water bodies. The soil P storage capacity (SPSC) has been proposed as a tool to estimate the capacity of humid region soils to act as either sinks or sources of P to runoff or leaching. The SPSC is based on a threshold molar ratio of extractable P/(Al+Fe), called the soil P saturation ratio (PSR), above which water‐soluble P abruptly increases. Objectives were to (i) document consistency of the threshold PSR for a wide geographic range of acid soils, (ii) determine applicability of a SPSC vs. water‐soluble P predictive equation to soils from various regions, and (iii) relate SPSC with water quality parameters. Surface samples were collected from acidic, humid‐region soils encompassing multiple physiographic provinces of the United States. Water quality data, including dissolved reactive P and total P, were obtained from various study sites. Phosphorus, Fe, and Al in Mehlich 3 solutions were determined, and PSR and SPSC calculated. The threshold PSR based on 186 samples is 0.1, indicating a common threshold across the geographic range of this study. Phosphorus concentrations in runoff related closely with SPSC, PSR, and M3‐P values of soils that were the source of the runoff. However, SPSC has the additional potential of estimating extent of legacy P loss at excessive concentrations for soils of eastern and central United States. Results support general applicability of PSR and SPSC for acid soils.