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