Cation exchange capicity and base saturation

this presentation describes cation exchange capacity and base saturation of soil solutions, and their effect on soil fertility

1. PRESENTED BY
AKHTAR MEHMOOD
ROLL # 11041706-010
DEPARTMENT OF BOTANY
M.PHIL BOTANY FINAL SEMESTER

2. Plant nutrient usually exist as ions i.e.
They carry an electrostatic charge.
The positively charged nutrients are known as Cations
while
Negatively charged nutrients are called as Anions.
Example.
Cations. Ca
2+,
Mg
2+,
,K
+
,Na
+
, H
+
,Al
3+
Anions: NO
3
-
,H
2
PO
4
-
,HPO
4
2-
,SO
4
2-
,Cl
-
History
From 1920s to 1940s William Albrecht did a lot of
experimenting with different ratios of nutrient cations.

3. Exchangeable Cations
Cations bound to soil in varying degree
Strongly bound to silica or Soluble in soil solution.
Between these two extremes are the exchangeable cations, which
are weakly bound to soil particles.
Soil particles carry net negative electrostatic charges as a result of
processes of soil weathering, and organic decomposition.
These sites of negative charges are most predominant in the
humus fraction of the soil, and on the edges of clay particles.
The bonding of these cations largely prevents their loss by
leaching, but is not so strong that plants cannot extract them from
the soil.

4. The Cation exchange capacity of a soil is a
measurement of its ability to bind or hold exchangeable
cations. In other words, it is a measure of the number of
negatively-charged binding sites in the soil.

5. Milli-equivalents (Meq.) of Selected
Cations and Their Equivalent ppm
Cation
Atomic
Weight
Valence
Milli-
equivalents
Equivalent
ppm Lbs/acre
H
+
1 1 1 10 20
Ca
++
40 2 20 200 400
Mg
++
24 2 12 120 240
K
+
39 1 39 390 780
NH
4
+
18 1 18 180 360
Al
+++
27 3 9 90 180
Zn
++
65 2 32.5 325 650
Mn
++
55 2 27.5 275 550
Fe
++
56 2 28 280 560
Cu
++
64 2 32 320 640
Na
+
23 1 23 230 460

6. Element Atomic
Weight
Valence Ppm to equal
1 milli
equivalent
Hydrogen 1 1 20
Potassium 39 1 390
Magnesium 24 2 120
Calcium 20 2 200

7. To determine the CEC calculate the
milliequivalents of H,K,Mg,Ca per 100 gm of
Soil(meq/100 g of soil)by using formula:
Formula
H,meq/100g soil=8(8.00-buffer pH)
K,meq/100g soil = lbs/acre extracted K/782
Mg,meq/100g soil= lbs/acre extracted Mg/240
Ca,meq/100g soil = lbs/acre extracted Ca/400
Na,meq/100g soil = lbs/acre extracted Na/460

8. Lab
#
Sampe
l#
Soil
code
Soil
pH
Buffe
r pH
P K Mg Ca Na
1133 4 5.17.70168 221 28 400 12

9. H,meq/100g soil=8(8.00-7.70)=2.40
K,meq/100g soil = 221/782=0.28
Mg,meq/100g soil= 28/240= 0.12
Ca,meq/100g soil = 400/400=1.00
Na,meq/100g soil = 12/460=0.03
Total CEC=3.83 meq/100g soil

10. Rating CEC (me/100g) Comment
Low 5-12 Low organic matter. Sandy
soil
Medium 12-25 Pumice soil, Lower fertility
High 25-40 High fertility soil, High
clay content.
Very High 40+ Peat soils

11. It refers to Elements that are basic or Alkaline in their
reaction.e.g K,Mg, Ca & small amount of Na & Al.
Hydrogen is an element with a positive charge and acts
like a cation however soils with significant saturation
of hydrogen are acidic, or have a lower pH.
The measure is expressed as milligram equivalents per
100 grams of soil or shortened to “me”.

12. Example
K=0.28meq/100g soil
Mg=0.12meq/100g soil
Ca=1.00meq/100g soil
Na=0.03meq/100g soil
CEC=3.83meq/100 g soil
Total for bases=K+Mg+Ca+Na=1.43meq/100g soil
Percent Base saturation= (1.43/3.83)(100%)=37%

13. Exchangeable Cations can be divided into two groups.
Bases
Acids
Every CEC binding site must have a cation bound to it,
to maintain electeroneutrality.
The soil pH Will be effected by whichever cations
predominate on these exchange sites.
More base cations more alkaline soil
More acid Cations more acidic soil

14. It is the fraction of the negative binding sites occupied
by bases.
For example
A base saturation level of 75% means that three out of
four sites are occupied by basic cations (remaining
25% by acidic cations).
Total base saturation is determined by following
formula
Total base saturation= Ca+Mg+K+Na
 CEC

15. CEC also helps to characterise soils.E.g
Organic matter is the major source of Negative
electrostatic sites there is a strong correlation between
CEC values, and the amount of organic matter in the
soil.

16. CEC can give insight into soil quality and site
characteristics.
Higher CEC likely indicates more clay, poor internal
drainage, limited structure and soil compactation in
high traffic areas.
Low CEC is indicative of sandy textured soils prone to
drought that invariably needs more organic matter to
improve water holding capacity, but have open grainy
structure that resist compaction.

17. What we have learned
Clay and organic matter have negative charges that can
hold and release positively charged nutrients.(The
cations are adsorbed onto the surface of the clay of the
clay or humus).That static charge keeps the nutrients
from being washed away, and holds them so they are
available to plant roots and soil microorganisms.

18. THANKS