ALKALINITAS CHAPTER VIII PENGELOLAAN TANAH BERLANJUT
Entisols, Mollisols, Orders TanahAridisols, : Alfisols, and Vertisols, dll Suborders: Ustic, Xeric, and Natric (SAR>15)
OUTLINE • Batasan Alkalinitas Tanah : Definisi, proses terbentuknya dan Penyebabnya • Karakteristik dan permasalahan alkalinitas tanah • Tanah Salin dan Sodik • Pengelolaan Alkalinitas Tanah
2 H+ + O-2
H2O
pH = - log [
+ H
+ H
OH
OH H+
OH-
Acid pH = 6.0
+ H ]
Neutral pH = 7.0
Alkaline pH = 8.0
Neutrality Acidity
Alkalinity
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, there are higher concentrations of carbonate and bicarbonate anions (due to dissolution of certain minerals) CaCO3 ↔ Ca2+ + CO32or NaCO3 ↔ 2Na2+ + CO32CO32- + H2O ↔ HCO3- + OHHCO3- + H2O ↔ H2CO3 + OH•pH rises more for most soluble minerals (eg. NaCO3) H2CO H2O +by COthe 3↔ 2(gas) •pH rise is limited 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:
• 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
Soil pH & nutrient availability
N P K Mg and Ca S B Cu and Zn Mo Fe Mn Al Fungi Bacteria & Actinomycetes 4
5
6
7 Soil pH
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
PERMASALAHAN PADA TANAH ALKALIN
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 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 pH will stimulate high levels of pHdependent charge
Soil clay dispersion • Penghancuran agregat • Penurunan makroporositas • 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 Na+
2+
Ca2+ and Mg
+ ++ ++ ++ ++ ++ ++++
+
+
+ +
+
+
S
EC
Lower EC Higher EC
Flocculated soil
Dispersed soil
Partikel tanah akan terflokulasi jika konsentrasi Ca2+ dan Mg 2+ lebih besar daripada konsentrasi Na+ (Nilai SAR rendah) Na+ + +
Ca
+
+
and Mg2+ ++ + + ++ + + + + +
Flocculated soil
SAR EC
Dispersed soil
Partikel tanah akan terdispersi jika konsentrasi Ca2+ dan Mg 2+ lebih rendah daripada konsentrasi Na+ (Nilai SAR tinggi) Ca2+ a nd Mg2+ ++ + ++ +
Na+ SAR ++ +
EC
Flocculated soil
+ +
+
Dispersed soil
Sodium adsorption ratio • Compares Na relative to Ca and Mg
SAR = [Na+]/ (0.5[Ca 2+] + 0.5[Mg2+])1/2 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
SALINESODIC No saline no sodic
>4
>15
>12
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. • 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)
Irrigation Gypsum
SODIC
>>8.5 can reach 10
>>Sodium
SALINESODIC No saline no sodic
>8.5
Ca, Mg, K and >>> Na Ca. Mg, K
Very diff. Add water Gypsum
>7<8.5
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 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.
