thanks

5.  .
 A soil with a neutral reaction contains equal
emount of H+ and OH- ions
 To characterize these conditions the term soil
pH is used

6.  In acid soils, more H+ than OH- ions are present.
Tanah masam (pH < 7) biasa ditemukan pada
kawasan humid. Most plants grow best in soils
with a slightly acid reaction. In this pH range,
nearly all plant nutrients are available in
optimal amounts.
 Tanah dengan pH <6 bisa mengalami kekahatan
beberapa hara yang dibutuhkan tanaman,
sebagai contoh Ca, Mg dan K.
 Pada tanah masam kuat dan sangat kuat, Al, Fe
dan Mn biasanya berada pada aras meracun
(toxic level). Unsur-unsur tersebut juga bereaksi
dengan fosfat membentuk fosfat tak larut.

7.  Tanah-tanah dengan pH >7 (tanah alkaline)
biasanya berada di dalam kawasan arid dan
semiarid. In basic soils, more OH- ions than H+
are present.
 Tanah alkaline mengandung Al, Fe dan Mn
dalam jumlah rendah oleh karena mengalami
presipitasi menjadi hidroksida Al, Fe dan Mn
tak larut.
 Pada tanah alkaline kuat, fiksasi fosfat juga bisa
menjadi masalah oleh karena membentuk
tricalsium fosfat yang tak larut.

8.  Loss of exchangeable bases from the soil CEC
 Leaching
 Removal from plant uptake
 Production of organic acids from organic matter
decay
 Use of fertilizers, particularly ammonium
sources: (NH4)SO4, NH4NO3, Anhydrous
ammonia, Urea

9.  Soil erosion: Loss of bases from surface runoff
 Parent material: Presence of acidic materials
that weather giving rise to acid soils
 Weathering

11. Ion hidroksi aluminium adalah produk hidrolisis ion Al3+ yang
melepaskan ion H+ selama reaksi. Ion aluminium dan produk
hidrolisisnya merupakan sumber ion H+ untuk kemasaman
aktif dan potensial.
As soon as an Al3+ ion is present in the soil solution, it is quckly
surrounded by six moleculs of H2O in octahedral
coordination, forming Al(H2O)6
3+. (aluminum hexahidronium
ion)

13. Al hydrolysis species at various pH values and their relative contribution to total
soluble Al

16. Ion Log K1 Log
1. Be2+ -6.5
2. Mg2+ -12.0
3. Ca2+ -12.5
4. Mn2+ -10.5
5. Fe2+ -7.0
6. Ni2+ -8.0
7. Cu2+ -7.5
8. Zn2+ -9.1
9. Cd -10.0
10. Hg2+ -3.5
11. Pb2+ -8.0
12. Al3+ -5.0 -5.5
13. Fe3+ -2.9 -3.3
14. La3+ -9.0
15. Ti4+ >-1
16. Th4+ -4.1

18.  Acid presipitation also know as acid rain is caused
by conversion of nitrogen oxide and sulfur dioxide
gases into strong acid. These gases are very
harmful to the enviroenment, plant growyth and
human health.
 SO2 + O2  2SO3
 3SO3 + H2O  H2SO4 (sulfuric acid)
 2NO + O2  2NO2
 2NO2 _+ H2o  HNO3 + HNO2 (nitric and
nitrous acid)

21.  Ammonium fertilizer:
 2NH4
+ + O2  2NO2
- + H2O + 4 H+ +
energy
 2NO2- + O2  2NO3
- + energy

23.  Equivalent acidity : the amount of lime
required per unit amount of fertilizer used to
bring the soil pH back to prefertilizer
application levels. Nilai bisa posirif atau
negatif.
 Dinamakan juga “Acidity Index”.
 Misal equivalen acidity ammonium nitrat =
593, berarti penggunaan 1000 kg ammonium
nitrat menyebabkan penurunan pH tanah yang
dapat dikembalikan ke pH semula dengan

24.  Pupuk fosfat
 Hidrolisis pupuk fosfat akan menghasilakan
orthophosphoric acid:
 Ca(H2PO4)2  CaHPO4 + H3PO4
(orthophosphoric acid)
H3PO4  H+ + H2PO4
-
H3PO4  2H+ + HPO4
-2
H3PO4  3H+ + PO4
-3

25.  Elemental sulfur: dapat digunakan untuk
merekayasa lingkungan tumbuh tanam supaya
menjadi masam. Oksidasi sulfur menghasilkan
asam sulfat yang dapat meningkatkan
konsentrasi ion H+ di dalam tanah.
 2So + 3O2 + H2O  2H2SO4

26.  Pyrite (FeS2)
 Oksidasi pirit, menghasilkan sulfuric acid
(H2SO4).
 FeS2 + 7H2O + 71/2 O2  4SO4
2- + 8H+ +
Fe(OH)3

27.  Biological Nitrogen Fixation:
 Nitrogen fixation alone does not contribute to
directly toward increasing the H+ ion
concentration in soils./
Ammonia levels increas considerably in the soil
due to ammonification of organic N from
nitrogen fixation. In a soil ecosystem where the
level of ionorganic nitrogen is in excess to that
needed by the growing plants, this excess of
ammonium will be nitrified, adding significant
amount oh H+ ions to the soil solution
(Kennedy)

29.  Potential, Reserve or Exchange Acidity 
Adsorbed H+ to colloid surfaces or other un-
dissociated H+ sources, that will react with
water to yield H+ (e.g. Al3+)
 Active Acidity  Presence of H+ in soil
solution soil pH
 Total Acidity = Potential Acidity + Active
Acidity

34.  pH can be viewed as an abbreviation for power of
concentration of hydrogen ion in solution
 pH = - [log (H+)] in solution
kw = pH + pOH kw = 14
14 = pH + pOH
pH = 14 - pOH

35.  Menetapkan pH tanah dengan pH (H2O) =
kemasaman aktif = aktifitas H+ pada larutan
tanah
 -H+ H+
 -H+ H+
 -H+ H+ H+
 -H+ H+
 Soil Colloid Soil Solution

48.  Considerations for correcting acidity
 Original soil pH
 Type of liming material and its fineness
 Availability of liming materials
 Type of soil (sandy, clayey, loamy, organic) and CEC
 Crop to be grown
 Depth of mixing in the soil
 Soil moisture

49.  Type of lime material
 Limestone:
 Calcite type (CaCO3)
 Dolomite type (CaMgCO3)
 Wood ashes (oxides of Ca, K and Mg)
 The type of lime to use depend on availability,
price, and type of soil. Dolomite type are
prefered when Mg is also deficient.
 The size of the limestone (coarse vs. fine) define
the degree of reactivity. Fine limestone is

50.  Buffering capacity in soils
 “Ability of a soil to resist a change in pH”
 Direct correlated with CEC of a soil, a high
CEC is associated with a large number of
exchange sites
 Example: High buffered soils are organic
soils, and 2:1clay soils. Low buffered soils are
low organic matter soils and 1:1 clay soils.

56.  CEC (Cation Exchange Capacity > 25
cmol(+)/kg atau 25 me%/100  tinggi
 CEC sedang 15 -25 cmol (+)/kg  sedang
 Derajat kejenuhan basa  kapasitas tanah
menyediakan basa-basa tertukar untuk
tanaman
 Derajat kejenuhan basa = jumlah kation
tertukar (Ca, Mg, K, Na) / KPK x 100 %

57.  KPK ditetapkan dengan metode NH4OAc
ammonium acetat pada pH 7
 KPK: kemampuan tanah menukar kation
KPK efektif = penjumlahan Ca+Mg+Na+K
Kation asam Al3+ dan H+
Kation basa Ca, Mg, Na dan K