Effects of Soil CEC on Turf

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

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 +

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

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

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 <3%

20. Plant Root Uptake of K Two main groups of K transporters: High affinity group which are very selective for potassium and reach their maximum uptake rate at low soil solution K concentrations Low affinity group which are less selective and require much higher soil solution K concentrations to reach their highest uptake rate. High concentrations of Ca, Mg, and Na can interfere with uptake. The proton pump pushes H+ out through the plasmalemma creating an electrochemical gradient (more negative on the inside). 25 to 50% of the energy flow in a root hair cell is used to drive the proton pump

21. Clay Effect on K Uptake

22. Optimum Percent Saturation Ranges 1.5-3 1.5-3 2-4 2-4 3-4 3-5 4-6 K% <5 <5 <5 <5 <5 <5 <5 Na% 5-20 60-80 30+ 5-20 60-80 26-30 8-20 60-80 21-25 8-20 60-80 16-20 8-20 60-80 11-15 8-20 60-80 6-10 10-20 60-80 0-5 Mg% Ca% Soil CEC

23. K Fertilizer Recommendations Example: Soil Test K = 45 ppm CEC = 5 Target K ppm (Table) = 116 ppm (subtract) Soil Test K = 45 ppm To be Applied 71 ppm Convert to K 2 O lbs/acre (x2.4) = 170 488 2.5 50 439 2.5 45 390 2.5 40 341 2.5 35 293 2.5 30 244 2.5 25 197 3 20 215 4 15 188 5 10 116 6 5 27 7 1 Target K ppm BCSR % CEC

24. Mg Fertilizer Recommendations Example: Soil Test Mg = 65 ppm CEC = 5 Target Mg ppm (Table) = 90 ppm (subtract) Soil Test Mg = 65 ppm To be Applied 25 ppm Convert to Mg lbs/acre (x2.0) = 50 600 10 50 540 10 45 480 10 40 420 10 35 360 10 30 300 10 25 240 10 20 210 12 15 160 13 10 90 15 5 18 15 1 Target Mg ppm BCSR % CEC

26. Elemental Sulfur lb/Acre Acidification 2600 1500 7.0 8.5 1400 800 7.0 8.0 700 400 7.0 7.5 CEC 8-15 CEC <7 Target pH Starting pH

27. Gypsum (CaSO 4 ) pH Correction Gypsum (tons/acre foot) = 1.7 x CEC x (Na% - 5%) CaCO 3 + H + (acid) = HCO 3 + Ca +

28. Comments or Questions?