Correlating total and extractable phosphorus for select mollisol soils

CHED 1077

Nicholas Schneider, schnein@southwestMSU.edu and Frank V. Schindler, schindlerfr@southwestMSU.edu. Department of Chemistry, Southwest Minnesota State University, 1501 State Street, Marshall, MN 56258
Phosphorus (P) is an essential nutrient input parameter for soil P loss indices, and its determination is necessary to develop Best Management Practices (BMPs). Knowledge of total soil P is useful in developing environmental management strategies that minimize loading of P to water resources. Total P is not routinely conducted in soil testing laboratories due to the rigors of digestion. Consequently, evaluating the correlation between standard soil test P indices and total P as a means of estimating total P from easily extractable P is of interest. Total P of select Mollisol soils was determined using mixed sulfuric and hydrofluoric acid digestion and ascorbic acid colorimetric procedures. Extractable P was determined by extracting a known quantity of soil with either: 1) 0.025 M hydrochloric acid plus 0.03 M ammonium fluoride, 2) sodium bicarbonate, or 3) a mixture of acetic acid, 0.25 N ammonium nitrate, 0.013 N nitric acid, 0.015 N ammonium fluoride, and 0.001 M EDTA. Total and extractable P relationships were analyzed using the method of least squares through standard SAS regression analysis. The significance of the relationships are discussed.