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

Lab
No.		 Sample
No.		 Soil
Code		 Soil
pH		 Buf.
pH		 P K Mg Ca Na
113282 3 4 5.1 7.70 168
VH		 221
H+		 28
L+		 400
L+		 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%