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ALKALINITAS
CHAPTER VIII
PENGELOLAAN TANAH BERLANJUT
Suborders:
Orders Tanah :Aridisols, Entisols, Mollisols, Alfisols, and Vertisols, dll
Ustic, Xeric, and Natric (SAR>15)Natric (SAR>15)
OUTLINE
• Batasan Alkalinitas Tanah : Definisi, proses
terbentuknya dan Penyebabnya
• Karakteristik dan permasalahan alkalinitas
tanahtanah
• Tanah Salin dan Sodik
• Pengelolaan Alkalinitas Tanah
pH = - log [ H+ ]
HH22O O 2 H2 H++ + O+ O--22
H+OH-
H+ OH-
H+
OH-
AcidAcidpH = 6.0pH = 6.0
NeutralNeutralpH = 7.0pH = 7.0
AlkalineAlkalinepH = 8.0pH = 8.0
Neutrality
AlkalinityAcidity
Alkaline and Saline Soils
•Saline soils occur in soils with pH>8.5
•Ca2+, Mg2+, K+ and Na+ do not produce acid upon
reacting with water
•They do not produce OH- ions either, but in soils with
pH>8.5,pH>8.5,
there are higher concentrations of carbonate and
bicarbonate
anions (due to dissolution of certain minerals)
CaCO3 ↔ Ca2+ + CO32- or NaCO3 ↔ 2Na2+ + CO3
2-
CO32- + H2O ↔ HCO3
- + OH-
HCO3- + H2O ↔ H2CO3 + OH-
H2CO3 ↔ H2O + CO2(gas)
•pH rises more for most soluble minerals (eg. NaCO3)
•pH rise is limited by the common ion effect
Sumber Alkalinitas
• Di daerah arid dan semiarid komplek pertukaran
didominasi: Ca2+, Mg2+, K+, Na+
• Adanya karbonat dan bikarbonat pada tanah
alkalin terkait dengan disolusi CO2:alkalin terkait dengan disolusi CO2:
• Kisaran pH reaksi tsb adalah antara 4,6 dan juga
8,6 (Ca-carbonates) atau 10 (Na-carbonates)
Calcium carbonate accumulation
in the lower B horizon
N
P
K
Mg and Ca
S
B
Cu and Zn
Mo
Soil pH &
nutrient
availability
Soil pH
Mo
Fe
Mn
Al
Fungi
Bacteria & Actinomycetes
4 5 6 7 8 9 10 10.4
PERMASALAHAN PADA TANAH
ALKALIN
1. Defisiensi Unsur Hara
2. Dispersi liat
Defisiensi Unsur Hara
1. Zn, Cu, Fe, dan Mn tidak terlarut pada
pH tinggi
Defisiensi Fe pada pohon
2. Ketersediaan Mo meningkat pada taraf meracuni tanaman, 3. Ketersediaan Cu menurun
4. Peningkatan kelarutan Ca dan Mg menghambat
pelarutan ion P
5. P berikatan dengan Ca membentuk ikatan Ca-P
yang tidak terlarut
6. Fungi, bakteri dan tanaman Brassica mengeluarkan
PERMASALAHAN PADA TANAH
ALKALIN
6. Fungi, bakteri dan tanaman Brassica mengeluarkan
asam organik untuk memecah ikatan Ca-P
CEC of alkaline soils
• Higher CEC than acid soils (assuming similar
texture and SOM)
• 2:1 type clays common in alkaline soils have
high permanent charge (e.g., smectite)high permanent charge (e.g., smectite)
• High pH will stimulate high levels of pH-
dependent charge
Soil clay dispersion
• Penghancuran agregat
• Penurunan
makroporositas
• Penurunan aerasi • Penurunan aerasi
• Penurunan perkolasi
• Retakan
http://www.agric.wa.gov.au/ikmp/images/F05790a.GIF
The white, rounded "caps" of the columns
are comprised of soil dispersed because
of the high sodium saturation
• Stabilitas Agregat (dispersi dan flokulasi)
tergantung keseimbangan SAR (antara Ca2+ dan
Mg2+ ) dan Na+ sama dengan jumlah garam
terlarut (EC) dalam tanah
+aNgMdna2+Ca
S
++
+
+
+++++++
++++
++++
2+
++
S
soilDispersed
Lower EC Higher EC
EC
soilFlocculated
Partikel tanah akan terflokulasi jika konsentrasi Ca2+
dan Mg 2+ lebih besar daripada konsentrasi Na+ (Nilai
SAR rendah)+aN
RA
++
+
+2gMdna+aC
RAS
soilDispersed
EC
soilFlocculated
++
++
++
++
+
+
+
Partikel tanah akan terdispersi jika konsentrasi Ca2+
dan Mg 2+ lebih rendah daripada konsentrasi Na+
(Nilai SAR tinggi)
+aNS A R
2+gMdna+2aC
+ +
+ ++ +
S A R
soilDispersed
+
++
EC
soilFlocculated
+ ++
Sodium adsorption ratio
• Compares Na relative to Ca and Mg
])1/2] + 0.5[Mg2+]/ (0.5[Ca 2+SAR = [Na+ ])1/2] + 0.5[Mg2+]/ (0.5[Ca 2+SAR = [Na+
SAR of 13 = ESP of 15
K could be included with Na
Types of Alkaline soils
TYPE Soil EC (mmhos/cm)
ESP (%) SAR
SALINE <4 0-15 0-12
SODIC 0-4 >15 >12
SALINE-SODIC
>4 >15 >12
No saline no sodic
0-4 0-15 0-12
How to manage alkaline soils
• Difficult to manage
• Before identify the type of management we have to identify the type of alkaline soil
• Every type (saline, sodic, saline-sodic) has a different management.management.
• In general any practice that reduces salt content will be needed .– Adding amendment (gypsum, OM)
– Leaching salts with clean water
– Irrigation techniques
– Utilizing salt tolerant crops
Types of Alkaline soils
TYPE Soil pH Typical ions Management
SALINE <8.5 Ca, Mg, K (chlorides
and sulfates)
IrrigationGypsumand sulfates) Gypsum
SODIC >>8.5 can reach 10
>>Sodium Very diff.Add water
SALINE-SODIC
>8.5 Ca, Mg, K and >>> Na
Gypsum
No saline no sodic
>7<8.5 Ca. Mg, K none
Alkaline soils can be black, why?
Because the high pH levels and high salt levels the organic matter becomes very disperse. The disperse humus moves upward in the capillary water flow, and upward in the capillary water flow, and when the water evaporates leaves a very intense black color on the soil surface.
So, not always black soils are good soils for food production.