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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #118311
Title: THE USE OF ISOTOPIC EXCHANGE KINETICS TO DETERMINE P AVAILABILITY IN OVERLAND FLOW AND SUBSURFACE DRAINAGE WATERS

Author
item MCDOWELL, RICHARD - PENN STATE UNIVERSITY
item SINAJ, SOKRAT - SWISS FED. INST. OF TECH.
item Sharpley, Andrew
item FROSSARD, EMMANUEL - SWISS FED. INST. OF TECH.

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2001
Publication Date: 7/20/2001
Citation: Mcdowell, R., Sinaj, S., Sharpley, A.N., Frossard, E. 2001. The use of isotopic exchange kinetics to assess phosphorus availability in overland flow and subsurface drainage waters. Soil Science. 166(6):365-373.

Interpretive Summary: The loss of phosphorus from soil to overland flow and subsurface drainage waters can adversely affect surface water quality. The potential for these losses is increased by the continued application of fertilizers and manures, causing a build-up of soil phosphorus concentration above that required for optimum plant growth. Recent evidence indicates that soil test phosphorus is related to phosphorus loss in overland flow or subsurface drainage waters. Although the release of phosphorus from soil to soil water is rapid, insufficient information is available on the kinetics loss to support improved soil phosphorus management. Thus, we conducted research to determine if phosphorus isotopes could be used to more accurately determine the kinetics of soil phosphorus release to water and thus, improve our understanding of the impacts of agricultural management on water quality. We found that phosphorus isotopes could be used to quantify the kinetics of soil phosphorus release to water. These methods have the potential to improve the prediction of phosphorus loss to overland flow and subsurface drainage waters.

Technical Abstract: The loss of phosphorus (P) on overland flow and subsurface drainage from soils receiving long-term applications of fertilizer and manure, has been linked to the accelerated eutrophication of fresh waters. This loss is initiated by the release of P from soil to solution, which for overland flow can be estimated by a water extraction and for subsurface drainage waters by 0.01 M CaCl2 extraction. Although this release is rapid, insufficient information is available on the kinetics P loss to support improved soil P management. In this study, an isotopic exchange kinetics (IEK) approach was used to assess the effect of two solutions (water and 0.01 M CaCl2) and different soil to solution ratios on soil P exchangeability (Et). Isotopically exchangeable soil P within 1 min (1:5 soil to solution ratio) was most closely correlated to the concentration of P in overland flow (r2 = 0.84 with water) and subsurface drainage waters (r2 = 0.93 with 0.01 M CaCl2). For overland flow, a correlation was maintained at a wider soil to solution ratio (1 to 100) for longer than other ratios (1 to 5 or 10) where no correlation existed. Similarly, the relationship between isotopically exchangeable P in 0.01 M CaCl2 (but not Et in water) and subsurface drainage waters P was maintained for up to 24 hr, reflecting the greater contact period of subsurface drainage water with soil compared to overland flow. The results show that the concentration of P in overland flow and subsurface drainage waters is dependent on the rapid or short-term (