Calculation of CEC with % clay and % OM Assume Avg CEC for % OM = 200 meq/100g Assume Avg CEC for % clay = 50 meq/100g CEC = (% OM x 200) + (% Clay x 50) From soil data: soil with 2% OM and 10% Clay 200 x.02 + 50 x.1 = 4 + 5 = 9 meq/100 g