Comparison of CEC By Addition Method Using Exchangeable Acidity Plus NH4OAc and Mehlich3 Extractable Cations with NH4OAc Distillation Method in Missouri Soils.

The University of Missouri soil test recommendations uses CEC for K recommendations and for calculating N credit based on soil organic matter. The current recommendations are based on NH4OAc extractable cations plus neutralizable acidity calculated from Woodruff Buffer pH test. Since FSA and NRCS requires all the federally assisted programs and nutrient management programs to use MU soil test recommendations, it has become important to compare the CEC by addition method using NH4OAC extractable cations vs Mehlich 3 extractable cations. Since most of the commercial labs uses Mehlich 3 extractant, and the extractable Ca and Mg by Mehlich 3 extractant are not same as NH4OAc extractable cations, it is timely to compare these two methods with the standard NH4OAC distillation method to ensure the MU soil test recommendations can be utilized to generate recommendations for Mehlich 3 extractable cations. One hundred soil samples received throughout the state of Missouri with varying soil pHs (1:1 0.01M CaC2), soil organic matter levels and CEC’s was selected in this study. The CEC estimation by addition method using buffer pH and exchangeable cations by NH4OAc and Mehlich 3 extractants will be compared with the standard NH4OAc distillation method and results will be presented.