1. Abstract Wisconsin requires Bray P1 as the routine soil test phosphorus method for fertilizer recommendations and phosphorus loss risk predictions. Highly calcareous soils (>5 g inorganic carbon/kg) have been shown to have the potential to neutralize the Bray P1 extracting solution causing erroneous fertilizer recommendations. Previous research has also shown that the carbonate dolomite (CaMg(CO 3 ) 2 ) does not affect the Bray P1 test whereas the much more soluble calcite (CaCO 3 ) does. Wisconsin has a region of calcareous subsoils located in the northeast part of the state where the carbonate has been identified as dolomitic, but there may be other calcareous regions in the state containing enough calcite to make Bray P1 an inappropriate choice for soil test phosphorus. The objective of this research is to establish a database of calcareous soils in Wisconsin and identify them as dolomitic or calcitic. A subsample of high pH (>7.0) soils (n=133) from Wisconsin was obtained from the UW Madison Soil Testing Lab. Samples were analyzed for pH, soil test P (Bray P1 and Mehlich 3), Bray P1 filtrate pH, total inorganic carbon (IC), and calcite and dolomite content. In summary, no soils with high levels of calcite were found in these 133 samples. Specifically, the soil pH ranged from 6.59-7.63; Mehlich 3 ranged from 10-225 mg P/kg soil; and Bray P1 ranged from 9-222 mg P/kg soil. Bray P1 filtrate pH ranged from 3.1-4.8, indicating that the Bray P1 extracting solution was not neutralized in any sample. The results of the calcite/dolomite volumetric calcimeter method corroborated these findings, with carbonate content ranging from 33-52 g calcite/kg soil and 0-88.3 g dolomite/kg soil. Total IC ranged between 0.1 – 11.0 g IC/kg soil. These findings give no evidence that Bray P1 is inappropriate for Wisconsin soils, but these 133 soils only begin the search for areas in Wisconsin that may contain high levels of calcite. I ntroduction 1. The Bray P1 soil test is composed of a weak acid solution and is used to measure available phosphorus in soil. (Bray and Kurtz, 1945, Frank et al., 1998) 2. Bray P1 is well correlated to Mehlich 3 and Olsen soil test P values, except on high pH or calcareous soils. (Hooker, et al., 1980; Mallarino and Blackmer, 1992; Mallarino, 1997; Mallarino, 2003; Fixen and Grove, 1990; Herman, et al., 2004; Randall and Grava, 1971). Note: pH>7.4 or calcium carbonate>4% (IC>5 g kg -1 ) 3. Bray P1 is neutralized by high levels of calcite (inorganic carbon > 5 g kg -1 ) but is not neutralized by dolomite. (Ebeling et al., 2007) 2HCl(aq) + CaCO 3 (s) → CaCl 2 (aq) + H 2 O(l) + CO 2 (g) 4. Bray P1 is required in Wisconsin for fertilizer recommendations, regulatory phosphorus management, and the Wisconsin phosphorus index. Therefore, Bray P1 needs to accurately predict phosphorus need. Question: Are there places in Wisconsin with significant calcite content, and thus require a soil P test other than Bray P1? Objective Establish a database of calcareous soils in Wisconsin and identify them as dolomitic (CaMg(CO 3 ) 2 ) or calcitic (CaCO 3 ). Experimental Approach 1. Gather soils from around WI (ongoing). 2. Determine calcite and dolomite contents. 3. Share information with UW soil lab and soil fertility experts. THUS FAR: Soils: +133 soil samples with high pH (Table 1) Analyses: +Bray P1, Mehlich 3 (Table 2) +pH, inorganic carbon, type of carbonate, BP1 filtrate pH (Table 3) Results Fig. 1: Bray P1 and Mehlich 3 correlate well (R 2 =0.9662); no indication that Bray P1 is being affected by carbonates in the soil. Fig. 2: Several soil samples have levels of inorganic carbon that could neutralize Bray P1 (IC>5 g kg -1 ). Fig. 3: Filtrate pH (of Bray P1 after shaking with soil) on all soils is <4.5, indicating no neutralization and that calcites are not likely present in large quantities. Fig. 4: Quantification of the amount of calcite and dolomite in these samples shows a baseline of calcite in these soils, but at levels low enough that Bray P1 phosphorus extraction will not be affected (as evidenced by data in Fig. 1 and 3). dolomite = CaMg(CO 3 ) 2 calcite = CaCO 3 Conclusions: √No highly calcitic sites were found √ Bray P1 still considered valid in Wisconsin √The search for calcitic sites in Wisconsin continues. Table 1. Information about the soils used. References: 1 Frank et al., 1998; 2 Mehlich, 1984. Table 2. Description of the P extractants used. AnalysisMethodReferences pH1:1 soil to water ratio Laboski et al., 2006 Total Inorganic Carbon Titrimetric method capturing CO 2 released from soil when HCl added Bundy and Bremner, 1972 Type of carbonate Volumetric calcimeter measuring CO 2 released Loeppert and Suarez, 1996 Bray P1 Filtrate pH pH of BP1 solution after shaking with the soil (and subsequent filtration) and before colorimetric P measurement Table 3. Other analysis performed on soils. Figure 2. Relationship between soil pH and inorganic carbon on a subset of soil samples from the database. Figure 3. Inorganic carbon versus Bray P1 filtrate pH on a subset of soil samples from the database. Establishing a database of calcareous soils in Wisconsin Angela M. Ebeling 1, Alexis Rwtambuga 2, and Matthew Flister 2 (1) Wisconsin Lutheran College: Assistant Professor of Biology; (2) Wisconsin Lutheran College: Undergraduate Researcher Figure 4. Results of the test to determine the type of carbonate present on a subset of soil samples from the database. References : Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of phosphorus in soils. Soil Sci. 59:39–45. Ebeling, A.M., L.G. Bundy, A.W. Kittell, D.D. Ebeling. 2008. Evaluating the Bray P1 test on high pH, calcareous soils. Soil Sci. Soc. Am. J. 72:985-991. Fixen, P.E., and J.H. Grove. 1990. Testing soils for phosphorus. p. 161–174. In Soil testing and plant analysis. 3rd ed. SSSA Book Series no. 3. Soil Sci. Soc. Am., Madison, WI. Herman, J.C., J.R. Massey, D.F. Leikam, and S. Harrold. 2004. Relationship of Mehlich-3 ICP and Mehlich-3 colorimetric phosphorus determinations with the Bray P1 extractant. North Central Extension-Industry Soil Fertility Conf., Des Moines, IA. 20:166–172. Frank, K., D. Beegle, and J. Denning. 1998. Phosphorus. p. 21–26. In J.R. Brown (ed.) Recommended chemical soil test procedures for the North Central Region. NC Regional Res. Publ. no. 221. Missouri Agric. Exp. Stn., Columbia MO. Hooker, M.L., G.A. Peterson, D.H. Sander, and L.A. Daigger. 1980. Phosphate fractions in calcareous soils as altered by time and amounts of added phosphate. Soil Sci. Soc. Am. J. 44:269–277. Mallarino, A.P., and A.M. Blackmer. 1992. Comparison of methods for determining critical concentrations of soil test phosphorus for corn. Agron. J. 84:850–856. Mallarino, A.P. 1997. Interpretation of soil phosphorus tests for corn in soils with varying pH and calcium carbonate content. J. Prod. Agric. 10:163–167. Mallarino, A.P. 2003. Field calibration for corn of the Mehlich-3 soil phosphorus test with colorimetric and inductively coupled plasma emission spectroscopy determination methods. Soil Sci. Soc. Am. J. 67:1928–1934. Mehlich, A. 1984. Mehlich III soil test extractant: A modification of Mehlich II extractant. Commun. Soil Sci. Plant Anal. 15:1409–1416. Randall, G.W., and J. Grava. 1971. Effect of soil:Bray no.1 ratios on the amount of phosphorus extracted from calcareous Minnesota soils. Soil Sci. Soc. Proc. 35:112–114. Soils # and location133 Jefferson and Dodge Counties, Wisconsin 1 Bray P1 (mg P kg -1 )9-222 Mehlich 3 (mg P kg -1 )10-225 pH6.59-7.63 Inorganic carbon (g IC kg soil -1 ) 2 0.1 – 11.0 Type of Carbonate (g kg soil -1 ) 2 Calcite33-52 Dolomite0-88.3 BP1 Filtrate pH 2 3.1-4.8 Acknowledgments:The authors gratefully acknowledge the staff at the UW Madison Soil Testing Lab for supplying soil samples with high pH. ExtractantType of Soil Composition Bray P1 (BP1) 1 Acid soils (pH<7)0.03 N NH 4 F, 0.025N HCl Mehlich 3 (M3) 2 Acid and alkaline soils Also cation extraction 0.2N CH 3 COOH, 0.25N NH 4 NO 3, 0.015N NH 4 F, 0.013N HNO 3, 0.001M EDTA Figure 1. Regression of Bray P1 and Mehlich 3 on the 133 soil samples currently in the database. 1 See highlighted areas in map to left. 2 These analyses were performed on a subset of samples that eliminated multiples from similar areas.