1. CATION EXCHANGE CAPACITY
and
PLANT NUTRITION

2. Cation Exchange Capacity (CEC)
Clay Particles and Humus
affect chemical properties of soil
complex structures with many negative charge sites
negative charge sites attract positive ions called cations

3. + attract cations from soil solution+
CEC
Negative charge sites are referred to as . . .
Cation exchange sites
+ attract cations from soil solution+

4. CEC Adsorption Force of attraction is called:
similar to force of a magnet holding iron filings

5.                              
Figure 3.10
Unlike charges attract, like charges repel.

7. CEC Cations can move on and off particles . . .
when one leaves, another replaces it
This process is called cation exchange, and cations involved are said to be exchangeable

9. CEC
The number of sites that a colloid (small particle) of charged clay or humus (micelles) contains is measured by the:
Cation Exchange Capacity expressed in mEq/100g
Note: newer units expressed in cmolc/kg

10. CEC may range from: 2.0 mEq/100g for sand to
> 50 mEq/100g for some clays
humus mEq/100g

11. CEC How fertile can a soil be?
Does applying more fertilizer always provide more nutrients to plants?
How much of the CEC is actually filled with cations?

12. CEC
The proportion of the CEC occupied by basic (+) nutrients such as Ca, Mg, K, Na, is called:
Percent Base Saturation and is an indication of the potential CEC of a given soil

13. CEC
Estimations that > 99% of cations in soil solution are adsorbed . . .
does not mean that percent base saturation is 99%

14. CEC
Example:
A soil with CEC of 10 mEq/100g has 6 mEq/100g of bases (Ca, Mg, K, Na) occupying exchange sites
What is the percent base saturation of the soil?

15. CEC
6 mEq/100g bases
10 mEq/100g sites
= 60 % base saturation

16. Cation Exchange is determined by:
CEC
Cation Exchange is determined by:
1) strength of adsorption
2) law of mass

17. CEC Strength of adsorption is as follows:
H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+

18. CEC Law of Mass the more of one ion available,
the greater the chance of adsorption

19. NUTRITION
There are at least 17 elements recognized as essential nutrients for plants;
we will recognize 18 elements:
C, H, O, P, K, N, S, Ca, Fe, Mg,
Mn, Mo, Cl, Cu, Zn, B, Co, Ni

20. NUTRITION
Nutrients grouped into 2 categories according to the relative amount used by plants:
Macronutrients – major elements; large amounts
Micronutrients – minor elements; small amounts
Both are essential for optimal plant production

21. NUTRITION Note: C, H, O . . . essential elements not considered in
nutritional studies;
Why?

22. NUTRITION > 95% of plant dry wt. from C, H, O;
(balance from macro, micro and other elements)

23. NUTRITION Except for C, H, O . . .
- Nitrogen (N) is present in greatest concentrations;
- Plants respond readily to Nitrogen (N)