Soil testing for phosphorus (P) is used agronomically to determine the amount of P needed for crop production. Soil test P is also used for determining environmental risks associated with elevated levels of soil P. The Bray P1 soil test method is commonly used in Wisconsin for measuring plant available P and is the required test for regulatory agencies. The Bray P1 extracting solution consists of 0.03 N ammonium fluoride and 0.025 N hydrochloric acid. The ammonium fluoride extracts mostly aluminum bound-P, and no iron-P, and the hydrochloric acid extracts calcium-P (Tandon et al., 1967). Mehlich-3 and Olsen are also widely-used soil test P methods. Mehlich-3 was developed for a wide range of soils including calcareous soils (Wang et al., 2004; Lucero et al., 1998), and Olsen was developed primarily for calcareous soils (Olsen et al., 1954). A calcareous soil is defined as a “soil containing sufficient calcium carbonate (often magnesium carbonate) to effervesce visibly when treated with cold 0.1 N hydrochloric acid” (Brady and Weil, 1999). Mehlich-3 and Bray P1 soil test results are highly correlated in neutral to acid soils with Mehlich-3 extracting slightly more P than Bray P1 in most soils because Mehlich-3 uses a more acidic extracting solution (Tran et al., 1990, Beegle and Oravec, 1990, Lucero et al., 1998; Mallarino, 2003). The Bray P1 soil test method is intended for acid soils, and the validity of its use to predict plant available P levels on the eastern red soils (ERS) in Wisconsin has been questioned due to concerns that the weak acid Bray P1 extracting solution could be neutralized by reaction with carbonates in these soils. Previous studies have found that Bray P1 extracts less P at higher soil pH (Mallarino and Blackmer, 1992; Mallarino, 1997; Atia and Mallarino, 2002) and that Bray P1 does not correlate as well as with Mehlich 3 or Olsen in soils with higher calcium carbonate contents (Hooker et al., 1980; Mallarino, 2003; Hermin et al., 2004). Mallarino (1997) found that Mehlich 3, Olsen, and Bray P1 correlated well with each other until soils reached a calcium carbonate equivalent (CCE) of 4% or higher. Other research indicates that pH alone is not a good indicator of when Bray P will fail; data shows that carbonate content greater than 36 g kg-1 (3.6%) is important (Mallarino and Atia, 2005). Mehlich 3 and Olsen soil test P results are well correlated regardless of soil type.