SoilCagmatReviewer5 sawsdawd adaddd ddd

SoilCagmatReviewer5.pdfSoilCagmatReviewer5.pdf

1. Chemical Properties of
the Soil
NonilonaP. Daquiado
Department of Soil Science
Central Mindanao University
Musuan, Bukidnon

2. ➢a system of very fine soil particles with an
upper diameter limit of 1 µm or µ
1 µm = 0.001 mm

3. Sand 2.0 –0.02 mm
Clay ≤ 0.002 mm
colloid
Silt 0.02 –0.002 mm
0.001 mm
Soil particle sizes?
0.0019
0.0012
0.0011
Clays but not colloids

4. represented by humus
clay of various kinds (silicate and non-
silicate clay minerals
☞There are more inorganic colloids compared
to the organic colloids
➢clay secondary mineral formedor
synthesized from primary minerals or their
weathering products

5. Limonite -Fe
2O
3.3H
2OHematite -Fe
2O
3
Gibbsite –Al(OH)
3
Boehmite–AlOOH
Manganite –MnOOH

6. Si surrounded by 4 O
Al surrounded by 6
O or OH
-
also called as silica
sheet
also called as
alumina sheet
sometimes called as tetrahedral sheet
sometimes called as octahedral sheet

7. ➢kinds due to differences in the arrangement of
the tetrahedral and octahedral sheets
➢1tetrahedral sheet
attached to one side of octahedral sheet
1Si sheet:1 Al sheet

8. ➢symmetrical arrangement of two tetrahedral
sheets about a central octahedral sheet
2Si sheet:1 Al sheet

9. presence of an octahedral sheet between
adjacent 2:1 layers
2Si :1 Al :1 Mg
Example: Chlorite

11. permanent charges in crystal lattice
replacement of a cation by another cation of
similar size but of different charge in the
tetrahedral or octahedral layer
pH-dependent charges
pH-dependent charges

12. ➢formed through isomorphoussubstitution
Kinds of charges based on their source

13. ➢reversible process by which ions
are exchanged between solid and liquid phases
exchange of cations
exchange of anions

14. IonExchange
K
+
H
+
H
+
H
+
OH
-
Na
+
K
+
H
2PO
4
-
OH
-
OH
-
OH
-
Al
3+
Mg
2+
H
+
Na
+
Al
3+
K
+
Mg
2+
Ca
2+
H
+
H
+
Mg
2+
H
+
H
+
H
+
NH
4
+
Mg
2+
K
+
H
+
OH
-
Cl
-
Mg
2+
NH
4
+
NH
4
+
Ca
2+
K
+
Na
+

15. Characteristics of cation exchange reactions are:
a. Concentration of the replacing cation
b. Relative replacing power of the cations
(Al
3+
, H
+
, Fe
3+
) > (Ca
2+
, Mg
2+
) > (NH
4
+
, K
+
)
> Na
+
c. Relative adsorbabilityof cations
amounts exchanged are
chemically equivalent
➢extremely rapid

16. # of me of a cation
weight of 1 me of cation
Equivalent weight
weight of 1 me of cation

17. ➢the total negativecharges on the soil
CEC = Σ# me cations/100g
= Σ# cmolcations/kg
➢capacity of the soil to hold and to exchange
cations
Sample problem:
1.A 100-g soil sample was found to contain 0.10g
Ca
++
, 0.004g H
+
, 0.048g Mg
++
, 0.092g Na
+
and
0.027gAl
+++
. Calculate the CEC of the soil.

18. Sample problem:
2. A 50-g soil sample was found to contain
0.09g NH
4
+
, 0.003g H
+
and 0.04g Ca
++
.
Calculate the CEC of the soil.

19. ➢refers to the extent at
which the exchange capacity of the
soil is saturated with bases
% BS

20. Exchangeable Sodium Percentage (ESP)
✰ESP refers to the proportion of the exchange
sites occupied by exchangeable Na
Soils with high ESP (> 15%) are considered
sodicsoil and need to be reclaimed

21. Percentage Aluminum saturation
➢the extent by which the exchange site is
saturated with Al
Aluminum saturation tolerance of some crops
Crop Critical Al saturation, %
Groundnut <65
Soybean <45
Corn <25
Mungbean <15

22. ➢capacity of the soil to hold and to exchange
anions
➢expression of the positivecharges of the soil
➢increases with the acidity of the soil
AEC = Σ# me anions/100g
= Σ# cmolanions/kg

23. ➢is a good indication of the amount of nutrients
available for your crops to absorb
➢the level of ability the soil water to carry or
conduct an electrical current
EC (µS/cm) Characteristics associated
< 200
low nutrient availability in the soil
may indicate a sterile soil with little
microbial activity
200 –1,200
> 1,200
good soil EC level
too much nutrients

24. EC (µS/cm) Characteristics associated
☞EC is also a measure of the amount of salts in
soil (salinity of soil)
0 –2,000
Non-saline;Salinity effects are
mostly negligible
2,100 –4,000
Slightly saline; Yields of very
sensitive crops reduced
4,100 –8,000
Moderately saline;Yields of many
crops reduced
8,100 –16,000
Strongly saline; Only tolerant crops
yields satisfactorily
> 16,000
Very saline; Only very tolerant
crops survive

25. ➢refers to degree of acidity or alkalinity of the
soil commonly expressed as pH
pH = -log [H
+
]
pOH = -log [OH
-
]
☞pH + pOH = 14
14
7
0
acidic : [H
+
] >[OH
-
]
basic : [OH
-
] >[H
+
]
: [OH
-
] =[H
+
]neutral
☞H
+
is the potential
determinant ion for
acidity
☞OH
-
is the potential
determinant ion for
alakalinity

26. Qualitativedescriptionofsoilreaction(Hoskins,1997):
pH RANGE
SOIL REACTION
DESCRIPTION
NORMAL CROP
RESPONSE
< 4.5 Extremely acid Very Poor*
4.5 -5.0Very strongly acidPoor*
5.1 -5.5Strongly acid Moderately good
5.6 -6.0Moderately acid Good
6.1 -<7.0Slightly acid Very good
>7.0 -7.5Slightly alkalineVery good
7.6 –8.0Mildly alkaline Moderately good**
8.1 -8.5Moderately alkalinePoor**
8.5 -9.0Strongly alkalineVery poor**
> 9.0 Very strongly alkalineFew grow

27. Acid forming processes in soils:
1.Continuous application of inorganic fertilizers
particularly the ammonium-containing fertilizer
(NH
4)
2SO
4
+ H
2O 2 NH
4OH + H
2SO
4
2 NH
4
+
+ 3O
2
2 NO
2
-
+ 4H
+
+ 2H
2O
2 NO
2
-
+ O
2 2 NO
3
-
☞Under aerobic condition, nitrification
would occur
Nitrosomonas
Nitrobacter
Nitrification ⇨conversion of NH
4
+
to NO
3
-

28. 2. Leaching of metallic cations taking place in
the exchange sites and replaced by H and Al
Acid forming processes in soils:
3. Production of CO
2during organic matter
decomposition
4. Inorganic acids such like H
2SO
4and HNO
3
which are components of acid rain
5. Cation uptake by plants or crop removal

29. 1. Active acidity➢H
+
concentration in soil
solution
2. Reserve (exchangeable) acidity
➢concentration of H
+
, Fe
3+
and Al
3+
ions
adsorbed by soil colloids
☞Generally, lime is applied to the soil when it
is acidic
☞Specifically, soils should be limed when its
pHfalls below the pH preference of a specific
crop

30. Crop pH preference
abaca 6.0 -7.0
ampalaya 6.5 –7.2
banana 6.0 –7.5
beans 5.5 –6.5
cabbage 6.0 –7.5
cacao 6.0 –7.0
coffee 5.5 –7.0
corn 5.5 –7.5
cowpea 5.0 –6.5
eggplant 5.5 –6.5
Crop pH preference
lanzones 5.5 –6.5
mango 5.5 –7.5
mungo 5.5 –6.5
peanuts 6.0 –6.5
pineapple 5.0 –6.5
Rice (paddy)6.0 –6.5
Rice (upland)5.0 –6.5
rubber 5.6 –8.0
sugarcane 6.0 –8.0
tomato 4.5 –6.5

31. ☞Soil pH is an initial basis for the prediction
of the chemical behavior of soils
particularly in relation to nutrient
availabilityand to microbial activity

32. ☞

33. pH and microbial activity
Strong
acidity
Moderate
acidity
Slight
acidity
Slight
alkaline
Moderate
alkaline
Strong
alkaline
4.0 5.0 6.0 7.0 8.0 9.0 10.0

34. ➢ability of the soil to
resist drastic changes in soil pH upon the
addition of lime or an acid
Factors contributing to buffering capacity of soils
➢As the organic matter content increases,
buffering capacity of the soil also increases
➢Generally, fine-textured soils have high
buffering capacity than the coarse-textured
soils

35. Problem soils in the Philippines
Problem Soils Area, ha%
Soils with severe fertility
limitations (acid soils)
11,760,00039.20
Acid sulfate soils 27,0000.09
Heavy cracking soils 765,3382.55
Peat soils 15,0000.05
Saline/sodic soils 400,0001.33
Soils of steeply sloping lands8,903,26229.69
Poorly drained soils 90,8800.30
Coarse textured soils 482,8491.61
Total22,444,32975.00