cation exchange capacity
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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CATION EXCHANGE CAPACITY
and
PLANT NUTRITION
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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
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CECNegative charge sites are referred to as . . .
Cation exchange sites
+ attract cations from soil solution+
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CEC
Force of attraction is called:
Adsorption
similar to force of a magnet holding iron filings
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Figure 3.10 Unlike charges attract, like charges
repel.
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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
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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
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CEC
may range from:
2.0 mEq/100g for sand
to
> 50 mEq/100g for some clays
humus 100-300 mEq/100g
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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?
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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
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CEC
Estimations that > 99% of cations in soil solution are adsorbed . . .
does not mean that percent base saturation is 99%
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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?
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CEC
6 mEq/100g bases
10 mEq/100g sites
= 60 % base saturation
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CEC
Cation Exchange is determined by:
1) strength of adsorption
2) law of mass
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CEC
Strength of adsorption is as follows:
H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+
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CEC
Law of Mass
the more of one ion available,
the greater the chance of adsorption
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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
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NUTRITIONNutrients 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
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NUTRITION
Note:
C, H, O . . .
essential elements not considered innutritional studies;
Why?
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NUTRITION
> 95% of plant dry wt. from C, H, O;
(balance from macro, micro and other elements)
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NUTRITION
Except for C, H, O . . .
- Nitrogen (N) is present in greatest concentrations;
- Plants respond readily to Nitrogen (N)