# Calculations

To determine the cation exchange capacity (CEC), calculate the milliequivalents of H, K, Mg, and Ca per 100g of soil (meq/100g soil) by using the following formulas:

• H, meq/100g soil = 8 (8.00 - buffer pH)
• K, meq/100g soil = lbs/acre extracted K ÷ 782
• Mg, meq/100g soil = lbs/acre extracted Mg ÷ 240
• Ca, meq/100g soil = lbs/acre extracted Ca ÷ 400
• Na, meq/100g soil = lbs/acre extracted Na ÷ 460

The total CEC will be the sum of the calculations from the 5 previous equations.

### Example

 LabNo. SampleNo. SoilCode SoilpH Buf.pH P K Mg Ca Na 113282 3 4 5.1 7.70 168VH 221H+ 28L+ 400L+ 12

• H, meq/100g soil = 8 (8.00 - 7.70) = 2.40
• K, meq/100g soil = 221 ÷ 782 = 0.28
• Mg, meq/100g soil = 28 ÷ 240 = 0.12
• Ca, meq/100g soil = 400 ÷ 400 = 1.00
• Na, meq/100g soil = 12 ÷ 460 = 0.03
Total CEC = 3.83 meq/100g soil

To calculate the percent base saturation, divide the sum of the K, Mg, Ca, and Na (the bases) in meq/100g soil by the CEC (all these values were calculated above). Multiply the result by 100%.

Example:

• K = 0.28 meq/100g soil
• Mg = 0.12 meq/100g soil
• Ca = 1.00 meq/100g soil
• Na = 0.03 meq/100g soil
• CEC= 3.83 meq/100g soil

Total for bases = K + Mg + Ca + Na = 1.43 meq/100g soil

Percent base saturation = (1.43 ÷ 3.83)(100%) = 37%