1. CEC Effects on Turf Soil Fertility Management Byron Vaughan, Ph.D.

2. Key Discussion Points

What is CEC

How CEC is determined

Factors affecting CEC

Fertility recommendations based on CEC

Soil acidification to improve nutrient availability

3. The Words Ca t ions and Anions

English physicist and chemist Michael Faradayintroduced the words anion for a negatively charged ion, and cation a for positively charged one in 1834. In Faraday's nomenclature, cations were named because they were attracted to the cathode in a galvanic device and anions were named due to their attraction to the anode.

4. Ca t ion Exchange Capacity

Ca t ion common positive charged soil nutrients

• Potassium (K +)

• Ammonium (NH 4 +)

• Sodium (Na +)

• Magnesium (Mg ++)

• Calcium (Ca ++)

• Zinc (Zn +)

• Manganese (Mn ++)

• Iron (Fe ++)

• Copper (Cu +)

• Acidity (H + )

Anion common negatively charged soil nutrients

• Nitrate (NO 3 - )

• Phosphate (H 2 PO 4 - )*

• Sulfate (SO 4 -- )

• Chloride (Cl - )

• Borate (BO 3 - )

• Molybdate (MoO 4 - -)

• Alkalinity Bicarbonate (HCO 3 - )

• *non mobile

5. + - - + + - + - N S N S S N N S Like poles (charges) repel Opposite poles (charges) attract SOIL COLLOID Ca 2+ K + Na + Mg 2+ SO 4 2- NO 3 - Cl - NH 4 + 6. Sources and Types of Soil Negative Charges

Sources

Clay

Organic Matter

Types of Charges

pH dependent CEC increases with higher pH

Soil CEC could be expected to increase up to 100% if the pH was changed from 4.0 to 6.5 and nearly double if the pH increased from 4.0 to 8.0.

pH independent pH has no effect on soil pH

7. Typical CEC of Soils and Soil Components 8. Typical Soil CEC Values 9. Common CEC Range Heavy Clay 50 CEC Sand 2 CEC CEC 25 More Clay, More Positions to Hold Cations CEC 5 Less Clay, Fewer Positions to Hold Cations K + Ca 2+ Mg 2+ NH 4 + Na + K + Ca 2+ K + Sand Clay 10. Measurement of CEC

Direct saturate soil with ammonium and then measure the amount of ammonium retained.

Indirect measure the amount of extractable Ca, Mg, K, Na, and H.

• CEC = Ca ppm/200 + Mg ppm/120 + K ppm/390 + [12 x (7-BpH)]

• Assumes all cations are on the exchange sites

Estimation

• CEC = OM% x 2 + Clay% x 0.50

• Assumes a mixture of clays types which are good estimates for young soils (high pH and low rainfall)

11. Cation Affinity for Negative sites

Generally ions with higher valency will exchange for those of lower valency.Al +++> Ca ++> Mg ++> K += NH 4 +> Na +

For ions of same charge, the cation with the smallest hydrated radius is more strongly absorbed because it moves close to the site of charge.

Relative amount high concentration of Na can replace Ca

12. Flocculating Power of Cations Cations in water attract water molecules because of their charge, and become hydrated.Cations with a single charge and large hydrated radii are the poorest flocculators. 0.96 1.08 0.53 0.79 Hydrated radius (nm) 43.0 2 Calcium 27.0 2 Magnesium 1.7 1 Potassium 1.0 1 Sodium Relative flocculating power Charges per molecule Cation Water molecule is polar:(+) on one end, (-) on the other end (+) (-) (+) Hydrated cation + 13. Effects of Cations on Soil Structure Negatively charged clay particle Negatively charged clay particle Dispersion/ Repel Clay particles behave independent of each other 14. Dispersed Soil Clay particles behave independent of each other. Poor Drainage 15. Effects of Cations on Soil Structure Negatively charged clay particle Negatively charged clay particle Flocculate Individual clay particles behave more as a larger aggregate + 16. Flocculated Soil Individual clay particles behave more as a larger aggregate 17. 18. The cations are fully hydrated, which results in repulsive forces and expanding clay layers (hydration energy). The water molecules wedge into the interlayer after adding water Dry condition (Interlayer) Clay layers cation 19. Nutrient Movement to Root Diffusion Dominant for K & P Mass Flow Dominant for Ca & Mg and anions Root Interception