Bahan Kajian MK. Dasar Ilmu Tanah. KTK & KETERSEDIAAN HARA. Smno.agroekotek.fpub.nop2013. Kapasitas Tukar Kation (KTK). Clay Particles dan Humus affect chemical properties of soil complex structures with many negative charge sites
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Clay Particles danHumus
Negative charge sites are referred to as . . .
attract cations from soil solution
Force of attraction is called:
similar to force of a magnet holding iron filings.
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
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
may range from:
2.0 mEq/100g for sand
> 50 mEq/100g for some clays
humus 100-300 mEq/100g
under certain soil conditions
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?
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
Estimations that > 99% of cations in soil solution are adsorbed . . .
does not mean that percent base saturation is 99%
Exchangeable nutrient cations adsorbed on soil particles exist in equilibrium with cations in the soil solution. Cations from the particles replenish those taken up from the soil solution by plants.
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?
6 mEq/100g bases
10 mEq/100g sites
= 60 % base saturation
Cation Exchange is determined by:
1) strength of adsorption
2) law of mass
Strength of adsorption is as follows:
H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+
Law of Mass
the more of one ion available,
the greater the chance of adsorption
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
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
Except for C, H, O . . .
- Nitrogen (N) is present in greatest concentrations;
- Plants respond readily to Nitrogen (N)