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An Environmental Threshold for Degree of Phosphorus Saturation in Sandy Soils
Author(s) -
Nair V. D.,
Portier K. M.,
Graetz D. A.,
Walker M. L.
Publication year - 2004
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2004.1070
Subject(s) - soil water , saturation (graph theory) , surface runoff , phosphorus , ammonium oxalate , soil test , soil horizon , environmental science , soil science , degree of saturation , chemistry , drainage , hydrology (agriculture) , mathematics , ecology , geology , inorganic chemistry , geotechnical engineering , organic chemistry , combinatorics , biology
There is critical need for a practical indicator to assess the potential for phosphorus (P) movement from a given site to surface waters, either via surface runoff or subsurface drainage. The degree of phosphorus saturation (DPS), which relates a measure of P already adsorbed by a soil to its P adsorption capacity, could be a good indicator of that soil's P release capability. Our primary objective was to find a suitable analytical protocol for determining DPS and to examine the possibility of defining a threshold DPS value for Florida's sandy soils. Four farmer‐owned dairy sprayfields were selected within the Suwannee River basin and soil profiles were randomly obtained from each site, as well as from adjacent unimpacted sites. The soil samples were divided either by horizon or depth, and DPS was determined for each soil sample using ammonium‐oxalate (DPS Ox ), Mehlich‐1 (DPS M1 ), and Mehlich‐3 (DPS M3 ) extracts. All methods of DPS calculations were linearly related to one another ( r 2 > 0.94). Relationships between water‐soluble P and DPS indicate that the respective change points are: DPS Ox = 20%, DPS M1 = 20%, and DPS M3 = 16%. These relationships include samples from Ap, E, and Bt horizons, and various combinations thereof, suggesting that DPS values can be used as predictors of P loss from a soil irrespective of the depth of the soil within a profile. Taking into consideration the change points, confidence intervals, agronomic soil test values, and DPS values from other studies, we suggest replacing Mehlich‐1 P values in the Florida P Index with the three DPS categories (DPS M1 = <30, 30–60, and >60%) to assign different P loss ratings in the P Index.