COMPARISON OF EXTRACTABLE PHOSPHORUS FROM 2 SULFURIC-ACID METHODS WITH THE MEHLICH PHOSPHORUS TEST NUMBER ONE

All mineral phosphates in soil dissolve more completely when HCl is mi xed with H2SO4 than with the HCl alone. It was hypothesized that a new extracting solution of H2SO4 alone with the same ionic strength or th e same acidity as the Mehlich P1 extractant would extract similar amou nts of soil phosphorus (P) as the Mehlich P1 soil test. Thirty six aci d soils from Alabama, Georgia, North Carolina, South Carolina, and Col orado were used in this study. These acid soils reflect wide ranges in parent materials, texture, pH, organic matter, and available soil P. They were analyzed for available soil P with the Mehlich P1 soil test and with the two H2SO4 methods: Method A has an extracting solution of same ionic strength (0.0875M) as the Mehlich P1 extractant, and Metho d B was an extracting solution of the same acidity (0.0375M) as the Me hlich P1 extractant. Correlations between the results of Mehlich P1 wi th Method A and Method B were 0.994 and 0.997, respectively. The measu red test precision was <3.5% for all three methods. The new H2SO4 meth ods are simple and faster to conduct under routine operations than the original Mehlich P1 extractant, and because of the high correlations, the H2SO4 methods should predict crop response to P as well as the or iginal Mehlich P1 extractant for acid soils.