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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #357343

Research Project: Sustaining Agroecosystems and Water Resources in the Northeastern U.S.

Location: Pasture Systems & Watershed Management Research

Title: Consistency of the threshold phosphorus saturation ratio across a wide geographic range of acid soils

item Dari, Biswanath - University Of Florida
item Nair, Vimala - University Of Florida
item Sharpley, Andrew - University Of Arkansas
item Kleinman, Peter
item Franklin, Dorcas - University Of Georgia
item Harris, Willie - University Of Florida

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2018
Publication Date: 9/13/2018
Citation: Dari, B., Nair, V.D., Sharpley, A., Kleinman, P.J., Franklin, D., Harris, W.G. 2018. Consistency of the threshold phosphorus saturation ratio across a wide geographic range of acid soils. Agrosystems, Geosciences & Environment. 1-8. doi:10.2134/age2018.08.0028.

Interpretive Summary: Given concerns over the environmental fate of phosphorus in soils, there is strong interest in predicting the outcome of future fertilization of a soil with phosphorus. This study evaluated an indicator of a soil’s ability to store phosphorus without adversely impacting water quality. Results confirm that this indicator provides a consistent measure across a wide range of soils and that it relates to water quality.

Technical Abstract: 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 of this study 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 USA. Water quality data, including dissolved reactive P and total P, were obtained from various study sites. Phosphorus, Fe and Al in a Mehlich 3 (M3) solution were determined, and PSR and SPSC calculated. The threshold PSR based on 186 samples is 0.1 (95 % confidence interval: 0.05 to 0.15; p<0.0001), 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 non-calcareous soils of the Eastern and Central USA.