Cation exchange capacity
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CATION EXCHANGE CAPACITY. and PLANT NUTRITION. 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. CEC.

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CATION EXCHANGE CAPACITY

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Cation exchange capacity

CATION EXCHANGE CAPACITY

and

PLANT NUTRITION


Cation exchange capacity cec

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


Cation exchange capacity

CEC

Negative charge sites are referred to as . . .

Cation exchange sites

+ attract cations from soil solution+


Cation exchange capacity

CEC

Force of attraction is called:

Adsorption

similar to force of a magnet holding iron filings


Cation exchange capacity

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


Cation exchange capacity

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


Cation exchange capacity

CEC

may range from:

2.0 mEq/100g for sand

to

> 50 mEq/100g for some clays

humus 100-300 mEq/100g


Cation exchange capacity

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?


Cation exchange capacity

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


Cation exchange capacity

CEC

Estimations that > 99% of cations in soil solution are adsorbed . . .

does not mean that percent base saturation is 99%


Cation exchange capacity

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?


Cation exchange capacity

CEC

6 mEq/100g bases

10 mEq/100g sites

= 60 % base saturation


Cation exchange capacity

CEC

Cation Exchange is determined by:

1) strength of adsorption

2) law of mass


Cation exchange capacity

CEC

Strength of adsorption is as follows:

H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+


Cation exchange capacity

CEC

Law of Mass

the more of one ion available,

the greater the chance of adsorption


Nutrition

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


Nutrition1

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


Nutrition2

NUTRITION

Note:

C, H, O . . .

essential elements not considered in

nutritional studies;

Why?


Nutrition3

NUTRITION

> 95% of plant dry wt. from C, H, O;

(balance from macro, micro and other elements)


Nutrition4

NUTRITION

Except for C, H, O . . .

- Nitrogen (N) is present in greatest concentrations;

- Plants respond readily to Nitrogen (N)


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