cation exchange capacity and plant nutrition cation exchange capacity (cec) clay particles and humus...
TRANSCRIPT
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CATION EXCHANGE CAPACITY
CATION EXCHANGE CAPACITY
and
PLANT NUTRITION
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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
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CECCECNegative charge sites are referred to as . . .
Cation exchange sites
+ attract cations from soil solution+
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CECCEC
Force of attraction is called:
Adsorption
similar to force of a magnet holding iron filings
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CATION ADSORPTIONCATION ADSORPTION
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CECCEC
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
http://www.une.edu.au/~agronomy/SSCATXCH.dcr
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CECCEC
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 (older unit) or cmolc/kg
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CECCECmay range from:
2.0 mEq/100g for sandto > 50 mEq/100g for some claysand
humus 100-300 mEq/100gunder certain soil conditions
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CECCEC
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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CECCEC
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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CECCEC
Estimations that > 99% of cations in soil solution are adsorbed . . .
does not mean that percent base saturation is 99%
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CECCEC
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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CECCEC
6 mEq/100g bases10 mEq/100g sites
= 60 % base saturation
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CECCEC
Cation Exchange is determined by:
1) strength of adsorption
2) law of mass
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CECCEC
Strength of adsorption is as follows:
H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+
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CECCEC
Law of Mass
the more of one ion available,
the greater the chance of adsorption
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NUTRITIONNUTRITION
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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NUTRITIONNUTRITION
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
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ROOT HAIR ABSORPTIONROOT HAIR ABSORPTION
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NUTRIENTS REPLACE CATIONS
NUTRIENTS REPLACE CATIONS
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NUTRITIONNUTRITION
Note:
C, H, O . . .
essential elements not considered innutritional studies;
Why?
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NUTRITIONNUTRITION
> 95% of plant dry wt. from C, H, O;
(balance from macro, micro and other elements)
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NUTRITIONNUTRITION
Except for C, H, O . . .
- Nitrogen (N) is present in greatest concentrations;
- Plants respond readily to Nitrogen (N)