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.