BAHAN KAJIAN MK. DASAR ILMU TANAH
K - TANAH
Diabstraksikan oleh:
smno.Jurstnhfpub.2012
KALIUM
TANAH
Jumlah K-tanah
Lithosfer mengandung 2.6% K
Tanah mengandung <0.1 - > 3%, rata-rata sekitar 1% K
Tanah lapisan olah (setebal 20 cm) mengandung <3000 - >100.000
kg K/ha
Sekitar 98% K dalam tanah terikat dalam bentuk mineral
Mineral Kalium
K-feldspar merupakan mineral utama sumber kalium, 16%
K-mika sekitar 5.2%, terdiri atas Biotit sekitar 3.8% dan Muskovit 1.4%
Kekuatan ikatan K dalam mineral
Kation K diameternya 2.66 Å, terbesar di antara unsur hara lain; oleh karena itu
ikatannya dalam struktur mineral lebih lemah dibandingkan kation lainnya yg
lebih kecil dan muatannya lebih besar.
Karena ukurannya besar, kation K dapat diselimuti oleh 7-12 ion oksigen,
sehingga kekuatan masing-masing ikatan K-O relatif lemah
KALIUM
dlm
FELDSPAR
KIMIA & struktur
Feldspar adalah aluminosilikat , formulanya KAlSi3O8,
kandungan kaliumnya 14%.
Di alam, sebagian kalium digantikan oleh Na dan Ca
Kation pusat
Si4+ sebagian digantikan oleh Al3+, satu
penggantian untuk setiap empat tetrahedra, sehingga menjadi
AlSi3O8-
Polimorf dari feldspar
Ortoklas: monoklinik - prismatik, dlm batuan plutonik
Sanidin
: Monoklinik, dalam batuan vulkanik
Microcline
: Triklinik, mengandung magmatit-pegmatit
Anortoklas
: Substituted feldspar, (K,Na)AlSi3O8
Nepheline
: Mengandung lebih banyak Na dp K
Plagioklas
: (Ca, Na feldspar) mengandung sedikit kalium
Pelapukan Mineral Kalium
Proses pelapukan fisik menghancurkan batuan induk, sedangkan pelapukan kimia akan
melepaskan ion K+ dari mineral
Temperatur penting untuk pelapukan fisika, sedang hidrolisis penting untuk kimiawi
Asam-asam yg penting pd hidrolisis mineral kalium adalah H2CO3 dan asam-asam organik
hasil dekomposisi Bahan organik tanah
HIDROLISIS
Feldspar
KALIUM
Abstraksi proses hidrolisis
KAlSi3O8 + HOH ===== HAlSi3O8 +K+ + OH- (Fase cepat)
HAlSi3O8 + 4HOH ===== Al(OH)3 + 3H2SiO3 (fase lambat)
Penambahan H+ mempercepat pembebasan K+ dan merusak ikatan Al-O; Al yang
dibebaskan membentuk gugusan AlOH2 koordinasi-4:
 Si-O-Al  + H2O + H+ ====  Si-O + Al-OH2 + K+
|
|
K
H
Hancurnya ikatan Si-O-Si mungkin disebabkan oleh melekatnya OH- ke Si sehingga
menjadi gugusan Si-OH; dengan cara ini ikatan kovalen rangkap dihancurkan.
Joint reaction H2O dan H+ dlm menghancurkan ortoklas:
3 KAlSi3O8 + 12H2O + 2H+ ===== KAlSi3O6.Al2O4(OH)2 + 2K+ + 6 H4SiO4
Pelapukan ortoklas menjadi kaolinit:
H2O
2KAlSi3O8 -------------- Al2Si2O5(OH) + 2K+ + 2OH- + 4H4SiO4
KALIUM
TANAH
Sumber K-tanah
Mineral primer yang mengandung kalium:
1. Feldspar kalium
: KAlSi3O8
2. Muskovit
: H2KAl3(SiO4)3
3. Biotit
: (H,K)2(Mg,Fe)2Al2(SiO4)3
Mineral sekunder:
1. Illit atau hidrous mika
2. Vermikulit
3. Khlorit
4. Mineral tipe campuran
Proses pelapukan mineral
KAlSi3O8 + HOH
KOH + HAlSi3O8
K+ + OHK
Ca
Koloid liat H
K+, Ca++, H+ (larutan tanah)
Pelapukan
1. Proses fisika: Penghancuran fisik, ukuran partikel
menjadi lebih halus, luas permukaannya menjadi lebih
besar
2. Proses kimiawi: Hidrolisis, Protolisis (Asidolisis)
Pelapukan
Mineral
KALIUM
Proses Hidrolisis dan Protolisis
HAlSi3O8 + K+ + OH- (cepat)
KAlSi3O8 + HOH
HAlSi3O8 + 4 HOH
 Si-O-Al  + H2O + H+
K
Al(OH)3 + 3 H2SiO3
 Si-O
(lambat)
+  Al-OH + K+
2
H
Pelapukan Ortoklas:
3 KAlSi3O8 + 12H2O + 2H+
KAlSi3O6 .Al2O4(OH)2 + 2K+ +6H4SiO4
H2O
2 KAlSi3O8
Al2Si2O5(OH) + 2K+ + 2OH- + 4 H4SiO4
Faktor
Pelapukan
Feldspar
KALIUM
Faktor Pelapukan
1. Faktor Internal
2. Faktor Eksternal
Faktor internal:
1. Regularity of the crystal lattice.
Microcline lebih stabil / sukar lapuk dibanding Ortoklas dan Sanidine
2. Na content of crystals. Anortoklas lebih mudah lapuk daripada ortoklas
3. Si content. Feldspar-substitusi lebih mudah lapuk dp Feldspar
4. Particle size. Semakin kecil ukuran partikel, maka semakin luas permukaannya
untuk mengalami reaksi hidrolisis dan asidolisis.
5. ………….
Faktor Eksternal:
1. Temterature. Proses pelapukan lebih cepat pd kondisi suhu yg lebih tinggi
2. Solution volume. Kondisi basah mempercepat proses pelapukan
3. Migration of weathering products. Proses pelapukan akan terhambat kalau
hasil-hasil pelapukan terakumulasi di tempat
4. The formation of difficult soluble products of hydrolysis.
Kalau hasil reaksi hidrolisis mengendap maka reaksi akan dipercepat
5. pH value. Semakin banyak ion H+, proses protolisis semakin intensif.
6. The presence of chelating agents.
MASALAH
KALIUM
TANAH
Ketersediaan K-tanah
Tanah mineral umumnya berkadar kalium total tinggi,
kisarannya 40 - 60 ribu kg K2O setiap HLO
Sebagian besar kalium ini terikat kuat dan agak sukar
tersedia bagi tanaman
Kehilangan akibat Pencucian
Sejumlah besar kalium hilang karena pencucian :
Tercuci dari tnh lempung berdebu
20 kg K2O/ha/thn
Diangkut /dipanen oleh tanaman
60 -”Konsumsi berlebihan: Luxury consumption
Tanaman dpt menyerap kalium jauh lebih banyak dari jumlah yg diperlukan
Pemupukan kalium harus dilakukan secara bertahap
Masalah Kalium tanah:
1. Pd saat tertentu sebagian besar K-tanah tidak tersedia
2. K-tanah peka terhadap pengaruh pencucian
3. Kalium dapat diserap tanaman dlm jumlah banyak, melebihi kebutuhan optimalnya
Kadar K-tanaman
(Tinggi)
Kadar K-tanaman
K diperlukan untuk
pertumbuhan optimum
Pemakaian berlebihan
Kalium yg diperlukan
(Rendah)
Rendah
K-tersedia dalam tanah
Tinggi
BENTUK & KETERSEDIAAN
Relatif tidak tersedia
Feldspar, Mika, dll. (90-98% dari K-total)
K segera tersedia
K dpt ditukar dan K dlm
larutan tanah
( 2 % dari K-total)
K lambat tersedia
K tidak dapat ditukar
(1 - 10 % dari K-total)
K tidak dapat
ditukar
K dapat ditukar
K dalam
larutan tnh
LOKASI DAN JALUR KALIUM DLM TANAH
K dalam mineral primer
mis. Muskovit
Pelepasan K
K dalam PUPUK
Fiksasi K pd
mineral primer
Transisi mineral sekunder
menjadi mika
akibat fiksasi
K
Pelepasan K
mengakibatkan
pembentukan
min. sekunder
K dalam mineral sekunder
mis. Kaolinit
Pelarutan
pupuk
K dalam
larutan tnh
Pelepasan Kdd
atau Kterfiksasi
Adsorpsi atau
Fiksasi K
Absorpsi K
K dalam tanaman
THE POTASSIUM CYCLE IN SOILS.
Potassium availability to plants in soil is
governed by the transfer between four main
pools in the soil: structural, fixed (nonexchangeable), exchangeable and soluble.
The soluble and exchangeable phases exist in
all soils, the latter providing negative charge
sites on clay mineral surfaces and organic
matter. The fixed or non-exchangeable phase
exists only in micaceous type clays (2:1
layers like illite, vermiculite and other clays
from this group).
In soils, equilibrium exists between these
different pools and the relationship between
them. The size of the soil solution pool is
very small, about 5 percent of total crop
demand at any given time, and 0.1-0.2
percent of the total soil K.
1. Römheld, V., and E.A. Kirkby. 2010. Research on
Potassium in Agriculture: Needs and Prospects. Plant
and Soil 335:155-180.
DIUNDUH DARI: ………http://www.ipipotash.org/en/eifc/2011/29/3/English#fig1.
Pelepasan K
dari mineral
primer
Pelepasan K dari mineral primer selama periode pertanaman
intensif; media tumbuh mineral dicampur pasir kuarsa. Ukuran
partikel mineral primer < 50 ; ukuran partikel illit < 20 .
Pelepasan K-tukar, g / g mineral
2000 Biotite
Illite
Muscovite
Ortoklas
400
5
10
15
cropping periode, (0-15) days
Sumber: Verma (1963)
Konsentrasi K-larutan tanah vs Kdd
K-larutan tanah (me/l)
5.0
Tanah berpasir
4.0
3.0
2.0
Tanah liat
1.0
10
50
K dapat ditukar, mg K / 100 g tanah
100
FIKSASI
KALIUM
TANAH
Faktor yg mempengaruhi fiksasi K-tanah
1. Sifat koloid tanah
2. Pembasahan dan pengeringan tanah
3. Pembekuan dan pencairan tanah
4. Adanya kalsium yg berlebihan
Koloid dan Kelembaban
Kaolinit sedikit mengikat kalium
Montmorilonit dan Ilit mudah dan banyak mengikat kalium, lazim
disebut dengan FIKSASI KALIUM:
lapisan liat 2:1
Ion kalium
Ion lainnya
Sisa tanaman &
Pupuk kandang
Pupuk
buatan
Mineral kalium
lambat tersedia
K - tersedia
Terangkut
tanaman
Hilang
pencucian
Hilang
Erosi &
Run-off
Fiksasi
Kalium
SIKLUS KALIUM
Soil Management: Building a Stable Base for Agriculture
Jerry L. Hatfield and Thomas J. Sauer (ed.). ISBN: 978-0-89118-195-8. Published: 2011
DIUNDUH DARI: ………. https://dl.sciencesocieties.org/images/publications/books/acsesspublicati/soilmanagementb/79.fig1.jpeg
Faktor
Ketersediaan Ktanah
1. MOBILITAS
Mobilitas kalium dalam tanah ditentukan oleh bentuk K+,
yaitu bentuk bebas dalam larutan tanah atau bentuk
terjerap pada permukaan koloid tanah
2. Interaksi dg ion lain
3. Mass flow dan Difusi
4. Kapasitas dan Intensitas
5. Mineral Tanah: Mineral Primer dan Mineral Liat
a. Kadar K mineral primer
b. Kecepatan pelepasan K+ dari mineral primer
c. Jumlah mineral liat
d. tipe mineral liat
6. Bahan Organik Tanah
7. pH tanah
8. Aerasi
9. Lengas Tanah
Difusi K+ dalam tanah terjadi melalui dua cara, yaitu:
1. Ruang pori yang berisi air, dan
2. Selaput air di sekeliling partikel tanah.
Pengaruh
pH
thd fiksasi K
Pengaruh thd fiksasi K
Pengaruh pH terhadap fiksasi K bersifat tidak langsung, yaitu
melalui pengaruh pH thd jenis aktion yg dominan pada posisi
inter-layer mineral liat.
Pd tanah masam Al+++ menempati posisi-posisi jerapan.
Pengasaman dapat mengakibatkan akumulasi ion Al-hidroksil pd
inter-layer mineral liat, shg KTK lebih rendah
Pada Vermikulit, ion Al+++ dapat mengusir K+ dari kompleks jerapan, sehingga
menurunkan kapasitas fiksasi K+.
Sehingga pengaruh pengasaman tanah thd fiksasi K tergantung pada adanya
vermikulit dan adanya Al+++ yg akan mendominir kompleks jerapan
Pengaruh pengapuran tanah masam thd fiksasi K tgt pada adanya Ca++ yg akan
menggantikan Aldd, shg membuka peluang terjadinya fiksasi K+
Fiksasi K+
K-released
pH: 3.50
Pupuk 100 kg K/ha
0.0
pH: 4.35
Tanpa pupuk K
Dosis kapur, CaCO3
pH: 7.00
K-adsorbed
Pencucian
Efek Pupuk K
terhadap
K-tanah
K-larutan tanah
pH: 4.1
pH: 5.1
pH: 6.5
pH: 7.0
Dosis pupuk K
Lengas Tanah
terhadap
K-tanah
Serapan K tanaman jagung
Pupuk Kalium:
49 mg K/100 g tnh
29
9
0
Kadar air tanah (20-40%)
Sumber: Grimme (1976)
Serapan K
vs
K-larutan tanah
Konsentrasi K+ dlm larutan tanah merupakan indeks
ketersediaan kalium, karena difusi K+ ke arah permukaan akar
berlangsung dalam larutan tanah dan kecepatan difusi tgt pada
gradien konsentrasi dalam larutan tanah di sekitar permukaan
akar penyerap.
Serapan K , kg /ha (Tanaman kacang buncis)
300
r2 = 0.79**
0.2
0.4
Sumber: Nemeth dan Forster (1976)
0.6
0.8
K- larutan tanah ( me K / l)
Laju
Penyerapan K
vs
Konsentrasi K+
larutan
Laju penyerapan K+ , mole/g/jam (akar tanaman barley)
10.0
0.05
Sumber: Epstein (1972)
0.10
0.15
0.20
Konsentrasi K+ larutan tanah ( mM)
Serapan K
vs
Dry matter
production
Growth & nutrient uptake, %
100
silking
tasseling
Biji
dry matter
Tongkol
Kalium
Batang
25
Sumber: Nelson (1968)
50
Daun
75
100
days after emergence
Relationship between soil available K and response of rapeseed to K
application
Determination of soil available K critical
level. Relationship between relative rapeseed
yield and soil available K level.
Relative rapeseed yields of CK/+K for all the
samples were positively correlated with soil
available K as determined by soil extraction with
ammonium acetate.
The soil available K data conformed to an
asymptotic relationship with relative yield as
interpreted using the logarithmic equation and
Cate-Nelson model.
The equation for describing the relationship
between relative rapeseed yield (y2) and soil
available K content (x) was y2 = 18.176ln(x) +
0.7444 (r=0.6583**; n=132).
It was concluded that the ability of soils to supply
K to plants and response of rapeseed yield to K
fertilizer application was reflected by soil
available K content.
DIUNDUH DARI: ………. http://www.ipipotash.org/en/eifc/2010/23/4
Kandungan Ktanah
vs
Respon pupuk
K
H
Tambahan hasil jagung , bu/ac
25
Kdd = 50 ppm
Kdd = 100 ppm
Kdd = 150 ppm
Kdd = 200 ppm
25
50
75
100
Dosis pupuk K ( lb / ac )
Sumber: Hanway et al. (1962)
125
Kandungan Kdaun
vs
Respon pupuk
K
Respon jagung thd pupuk kalium dipengaruhi oleh status K
tanaman, yaitu kadar K daun pada fase silking
Defisiensi akut
: Kadar K daun 0.25 - 0.41 %K
Defisien tanpa gejala:
0.62 - 0.91 %K
Normal
:
0.91 - 1.3% K
Tambahan hasil jagung , bu/ac
25
Kdaun = 0.75 %
Kdaun = 1.0 %
Kdaun = 1.5 %
Kdaun = 1.75%
25
50
75
100
Dosis pupuk K ( lb / ac )
Sumber: Hanway et al. (1962)
125
Yield response to applied K
Relationship between grain yield to applied K
and soil available K level.
K fertilizer application was thus shown to have
a positive effect on grain yield in most trials.
The figure describes the relationship between
soil K available content (x) and yield response
(y1) in the experimental plots.
The equation was y1 = -374.67ln (x) + 1,933.1
(r=0.6653**; n=57).
The high variability of grain yield in response
to applied K between experimental sites
probably relates to site differences in soil K
status at transplanting and differences in
environmental conditions during growth.
For example, the available K was only 42.3
mg kg-1 at Hubei Ezhou, and the +K treatment
increased yield by about 42.5 percent
compared with the CK treatment. By contrast,
at Hubei Honghu, Jiangxi Shanggao and
Zhejiang Shaoxing, where the soil available K
was much higher, the increasing rate raised
yields by only less than 10 percent.
DIUNDUH DARI: ……….
Potassium in Soils
Relationship among unavailable, slowly available,
and readily available potassium in the soil-plant
system.
The total K content of soils frequently
exceeds 20,000 ppm (parts per million).
Nearly all of this is in the structural
component of soil minerals and is not
available for plant growth. Because of
large differences in soil parent materials
and the effect of weathering of these
materials in the United States, the
amount of K supplied by soils varies.
Therefore, the need for K in a fertilizer
program varies across the United States.
Three forms of K (unavailable, slowly
available or fixed, readily available or
exchangeable) exist in soils. A
description of these forms and their
relationship to each other is provided in
the paragraphs that follow.
DIUNDUH DARI: http://www.extension.umn.edu/distribution/cropsystems/dc6794.html……….
Readily Available Potassium :
Potassium that is dissolved in soil water
(water soluble) plus that held on the
exchange sites on clay particles
(exchangeable K) is considered readily
available for plant growth. The exchange
sites are found on the surface of clay
particles. This is the form of K measured by
the routine soil testing procedure.
Plants readily absorb the K dissolved in the
soil water. As soon as the K concentration in
soil water drops, more is released into this
solution from the K attached to the clay
minerals. The K attached to the exchange
sites on the clay minerals is more readily
available for plant growth than the K
trapped between the layers of the clay
minerals.
The relationships among slowly available
K, exchangeable K, and water-soluble K are
summarized below.
DIUNDUH DARI: ……….
slowly available K
exchangeable K
water-soluble K
Potassium in Soil
Types of Potassium in Soil:
Potassium in soil is generally classified into
four types:
Unavailable Potassium
Fixed potassium or Slowly Available Potassium
Exchangeable potassium or Readily Available
Potassium
Soil solution potassium
Fixed potassium – potassium that becomes
slowly available to plants over the growing
season. Clay minerals have the ability to fix
potassium. During wetting and drying of the
soil, potassium becomes trapped in-between the
mineral layers (clay minerals have a layer
structure). Once the soil gets wet, some of the
trapped potassium ions are released to the soil
solution. The slowly available potassium is not
usually measured in regular soil testing.
DIUNDUH DARI: http://www.smart-fertilizer.com/articles/potassium-in-soil……….
The Potassium cycle in the soil-plant-animal system (from SYERS,
1998)
. Syers, J.K. (1998): Soil and plant potassium in agriculture. Proceedings No. 411, The International Fertiliser
Society York, UK. 32 pp.
DIUNDUH DARI: http://www.ipipotash.org/presentn/aspcwdb.html……….
AGR-11 . POTASSIUM IN KENTUCKY SOILS . ISSUED: 5-73
REVISED: by Lloyd Murdock, and Kenneth Wells, Extension Specialists in Agronomy, University of
Kentucky College of Agriculture
Total Potassium Content of the Surface 7
Inches of Soils on Experiment Fields in
Kentucky
Soil Class
Location of
Experiment Field
Total Potassium
Content (lbs/A)
Maury silt loam
Lexington
29,000
Crider silt loam
Princeton
(limestone)
32,600
Tilsit silt loam
Princeton
(sandstone)
30,000
Monongahela silt
loam
Berea
19,000
Welston silt loam
Fariston (Laurel
Co.)
24,400
Bedford & Dickson
silt loam
Campbellsville
13,000
Tilsit catena silt
loam
Greenville
24,600
Grenada silt loam
Mayfield
29,700
DIUNDUH DARI: ………. http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm
POTASSIUM AND PLANT
There are three forms of K in the soil:
Soluble K is the smallest portion of
the total soil K. By supplying current
plant needs, annual applications of K
minimize losses of this element.
Exchangeable K is held on the soil
colloids and is readily available to
plants. This fraction also makes up a
small percentage of the total K in the
soil.
Non exchangeable K is held within
the clay fraction of the soil and is
neither soluble nor available to
plants. Non exchangeable K makes
up the largest portion of total K in the
soil, except in highly acid, sandy
soils or on soils that are high in
organic matter, where non
exchangeable K levels are relatively
low. As soil minerals weather, non
exchangeable K gradually becomes
available.
DIUNDUH DARI: ………. http://www.spectrumanalytic.com/support/library/ff/Alfalfa_and_Potassium.htm
. Potassium Fixation and Release
With the application of potassium fertilizer, potassium first goes into the soil solution, soon after which much of it goes
into the exchangeable and some to the nonexchangeable forms. As crops remove the readily available potassium, the
reactions are reversed and exchangeable potassium goes into the soil solution. As a result there is constant fixation and
release of potassium in the soil.
During weathering, physical, chemical, and biological forces act on the parent materials and break them down into finer
fractions, largely sand, silt, and clay size particles. This breakdown results in the release of several chemical elements,
including potassium, and the formation of different clay minerals.
Most of the total potassium inherited from the parent material during the soil forming processes will be in the
nonexchangeable and exchangeable forms. Both exchangeable and nonexchangeable potassium are sources of readily
available potassium and that the process is reversible.
The relative amounts of
sand, silt and clay
fractions found in a soil
depend on the kind of
parent material
(sandstone, limestone,
shale or mica) from
which the soil was
derived. Potassium
fixation and release is
greatly influenced by
the relative amounts of
these fractions and the
kinds of clay minerals
present in the soil.
DIUNDUH DARI: ………. http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm
Soil Potassium and Clay Minerals
Clay minerals (the dominant materials in the clay or colloidal fraction) in a soil are relatively active in fixing
and releasing potassium. The different types of clay minerals vary in their capacity to fix and release
potassium. Generally there are four dominant clay minerals in Kentucky soils. Listed here in order of their
abundance, they are kaolinite, soil mica or illite, vermiculite, and montmorillonite. No soil is composed of
only one of these and, usually, a soil will contain as many as three or four. Each clay mineral has its own
characteristics with respect to potassium fixation and release. In addition, each clay mineral contains different
amounts of native potassium, which is bonded between the clay layers.
Because of their crystal structure and the location and amount of negative charges within the crystals, illite
and vermiculite clays are capable of absorbing potassium from the soil solution and entrapping it between
layers of the clay particle. The potassium cations are fixed or entrapped in this way because of the
relationship of their size to the hexagonal cavities in the silica sheets of two adjoining mica or vermiculite
layers. This fixed, or nonexchangeable, potassium is not available to plants but is slowly released as the
levels of exchangeable and soil solution potassium become lower.
The Kaolinite does not have potassium entrapped
between the layers. Soils containing
predominantly the kaolinite clay mineral have
less exchangeable potassium to release than soils
which have a higher percentage of the mica and
vermiculite type clay minerals. The
montmorillonite mineral can hold large amounts
of exchangeable potassium, but will fix only a
small percentage of it. Therefore, most of the
potassium held by montmorillonite clay is in an
available form.
DIUNDUH DARI: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm……….
Soil Potassium and Cation Exchange
Ions with a positive (+) charge are referred to as "cations," while those with a negative (-) charge are referred to as "anions."
The interaction of potassium and other cations, such as calcium and magnesium, with the soil colloids is referred to as "cation
exchange.“
The importance of cation exchange capacity (CEC) is that it prevents or reduces the leaching of fertilizer components such as
potassium, ammonium, magnesium, calcium, and other cations. Cation exchange is a means by which the soil can store
potassium and other cations that may be released later to plants.
The contribution of the clay mineral fraction to the cation exchange capacity is dependent on both the kinds and amounts of
minerals in the soil. The contribution of humus depends on the amount in the soil; though in most Kentucky soils the humus
content is, on a percentage basis, very low. While the clay minerals and humus account for most of the CEC, the finer
fractions of the silt can also have a limited number of exchange sites.
Of the clay minerals, kaolinite has the lowest CEC (5 to 15 me/100 grams). The CEC of illite is intermediate (10 to 45
me/100 grams), while montmorillonite and vermiculite clay minerals are relatively high (60 to 150 me/100 grams). The CEC
of humus is about 140 me/100 grams. These values are for pure clay minerals or humus.
The sand and silt fractions account for roughly 75 to 85 percent of the
weight of silt loam soils and contribute little to the CEC. The 15 to 25
percent of clay minerals in silt loam soil along with the smell amounts
of humus in the surface soil is largely responsible for the CEC. While
CEC determinations are not routinely made on soil samples tested in
Kentucky soil testing laboratories, most of the silt loams in Kentucky
have a CEC of 8 to 12 me/100 grams.
Cations on the exchange sites are held rather loosely on the edges of the
clay mineral or humus particles and are constantly being replaced by
other cations. They occupy exchange sites because they are balancing
the negative charges of the clay minerals and humus fractions in the
soil. For this reason the reactions are reversible.
DIUNDUH DARI: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm ……….
POTASSIUM CYCLE
Potassium is taken up by plants in
large quantities and is necessary to
many plant functions, including
carbohydrates metabolism, enzyme
activation, osmotic regulation, and
protein synthesis. Potassium is
essential for photosynthesis, for
nitrogen fixation in legumes, starch
formation, and translocation of
sugars.
As a result of several of these
functions, a good supply of
potassium promotes production of
plump grains and large tubers.
Potassium is important in helping
plants adapt to environmental
stresses (e.g. improved drought
tolerance and winter hardiness,
better resistance to fungal diseases
and insect pests
DIUNDUH DARI: ………. http://www.tankonyvtar.hu/en/tartalom/tamop425/0032_talajtan/ch09s05.html
Equilibrium relationships between forms of potassium in soils.
Soil Potassium exists in the soil in several forms.
Plants absorb potassium (K+) from only the ionic form
in soil solution. Exchangeable potassium from the soil
colloids (clays and humus) is readily available, for this
form enters easily into the soil solution.
Nonexchangeable potassium is fixed in the lattice
structure of clays. It is trapped in the structure and is
not released unless some mechanism opens the lattice
to permit the potassium to diffuse into the soil
solution. The nonexchangeable fraction is from 2% to
10% of the total soil potassium and represents a
reservoir of slowly available potassium from which a
plant may draw during the growing season.
The release of potassium from the nonexchangeable
sites depends on the types of clay, moisture, pH, and
presence of other cations in the soil. Almost all of the
potassium in the soil is in the primary minerals or
slowly available fraction. These primary minerals are
feldspars and micas, which are derived from the
weathering of rocks from the parent material. They are
resistant to weathering further and are very slowly
soluble; hence, the amount of potassium released from
this fraction is very small although the total amount
present is large.
DIUNDUH DARI: ………. http://people.umass.edu/psoil120/guide/chapter7.htm
THE POTASSIUM CYCLE
Potassium is supplied to the soil solution
(and hence to plant roots) mainly by
mineral weathering and by cation exchange
on colloid surfaces. Organic matter
mineralization has little effect as potassium
readily leaches out of plant residues and so
is not a structural component of soil
humus. Certain 2:1 type clays, especially
vermiculite, can fix potassium ions in
interlayer positions that become
inaccessible to normal cation exchange and
to root uptake.
In some soils mineral weathering can
supply potassium fast enough to maintain a
sufficient supply of soluble and
exchangeable K. In other soils, however,
continued removal of high potassium crops
can deplete the available soil supply faster
than natural weather can replenish it.
Potassium is not lost from soils as gaseous
forms, but both leaching and erosion losses
can be substantial.
DIUNDUH DARI: ………. http://faculty.yc.edu/ycfaculty/ags105/week12/biogeochemical_cycles_information/biogeochemical_cycles4.html
Soil Potassium
There are approximately 24,000 lbs of K per acre, so it is certainly not in short supply, even considering the
amount alfalfa requires. So why add any? To begin with, K occurs in at least three main forms: soil solution,
exchangeable, and mineral. Like other nutrients, K is taken up by plant roots only from the soil solution; and
yet, K in solution represents a very small fraction of the total K in soil. The soil solution must be replenished
with K from other sources in the soil to meet the need of a growing crop. That replenishment comes primarily
from readily available, “exchangeable” K.
Exchangeable K, like other positive charged
ions such as magnesium (Mg), calcium (Ca),
and aluminum (Al), is loosely held in soil by
an attraction to the negative charged surfaces
of soil particles, somewhat like magnets on a
refrigerator (Figure 2). The amount of
negative charge in a soil is a characteristic of
that soil and is called the soil’s cation
exchange capacity (CEC). When K is added
to soil it occupies negative charged sites on
soil particles by “kicking off,” or exchanging
with, other positive charged ions. This CEC
holds K in ready reserve to supply the need
of a small grain crop or the much greater
need of an alfalfa crop. As plant uptake
occurs, K is released from these sites to the
soil solution in quantities dependent on both
the amount of K present and the proportion
of the CEC sites it occupies.
DIUNDUH DARI: ………. http://extension.psu.edu/cmeg/facts/agronomy-facts-14
Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir
Subhash Chand and Tahir Ali
Universal Journal of Environmental Research and Technology. 2011 Volume 1, Issue 3: 373-375
The potassium releasing capacity of fifteen soil samples of Anantnag district of Kashmir
were assessed by using five chemical extractants.
The decreasing order of potassium release by the different chemical extractants in the soils
was 1M HNO3 > 0.01 N HCl--12 extractions>0.01 N HCl--9 extractions> 0.3 N NaTPB-16
hours > 0.01N HCl 3 extractions> 1.38N H2SO4=0.01N HCl-1 extractions> % K
saturation.
The K released by 1M HNO3 was significantly correlated with 1.38N H2SO4 (0.995**)
and 10.28 N H2SO4 (0.996**) .
The significant correlations among different form of K in Anantnag soils indicate the
various K pools (exchangeable=Non-exchangeable) for proper K fertilizer management.
The potassium status in Anantnag soils was variable.
DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert-1-317.pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZpszkrg_GHDA……….
Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir
Subhash Chand and Tahir Ali
Universal Journal of Environmental Research and Technology. 2011 Volume 1, Issue 3: 373-375
Potassium releasing and supplying power of the soil are often used as synonyms. A knowledge of the rate of potassium
release from soil might play an important role for comparing capacities of soil to supply potassium to plants (Srinivasrao
et al., 2001). The release of non- exchangeable potassium occurs when the levels of exchangeable K and soil solution K
are decreased by crop removal and leaching. No work has been reported so far on the suitability of various K test
procedure for their suitability to measure K release from Anantnag district soils of Kashmir.
The number of studies have been previously carried out regarding the evaluation of K releasing methods in various
ecological and groups of soils using different test crops ( Yadav,1983,Patiram and Prasad,1991 and Singh 1995) .A
critical appraisal of the results of carried out investigations indicate that no methods has been found appropriate under all
situations /locations. This is because of wide variation in the soil, type of plant and experimental techniques. The similar
studies have been carried out for knowing variability in potassium forms in different soils and their capacity to release
the same by Subhash Chand et.al (2009) and Subhash Chand,2010.
1. Partiram and Prasad, R.N. (1991): Release of None-exchangeable Potassium and its Relation to Potassium Supplying Power of Soils.
Journal of the Indian Society of Soil Science.39:488-493.
2. Shrinivasrao, C., Subbarao, A., and Rupa, T.R. (2001): Need for Inclusion of Non- exchangeable Potassium as a Measure in Soil Test
Calibration and Potassium Recommendations. Fert. News, 46: 31-38.
3. Singh, R.K (1995): Potassium Fertility Characterization of Two Soils Series of Rajasthan .PhD Thesis. Rajasthan Agriculture
University,Bikaner.pp212.
4. Subhash Chand, Tahir Ali and N.A. Kirmani (2009): Potassium Releasing Power of some Anantnag district soils of Kashmir. Poster paper
presented in 9 th Agriculture Science Congress held at SKUAST-K, Shalimar pp24.
5. Subhash Chand (2010): Assessment of Potassium Release by Different Chemical Extractants in Soils of Eastern Rajasthan. Journal of
Research, SKUAST-J, 9:1:108-113.
6. Yadav,B.S. (1983): Relative Crop Response and Redefining of Critical Limits of Potassium in Red soils of Critical Limits of Potassium
in Red Soils of Rajasthan. PhD Thesis. Univ. of Rajasthan, Udaipur.
DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert-1-317.pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZpszkrg_GHDA……….
Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir
Subhash Chand and Tahir Ali
Universal Journal of Environmental Research and Technology. 2011 Volume 1, Issue 3: 373-375
The Anantnag district soils were found variable in their K releasing power. The hot
1M HNO3 was found most suitable extractants on the basis of their concentration
used, time consumed in extractions, coefficient of correlation with other
extractants and soil properties.
Hot Nitric acid methods (1M HNO3 ): Five gram soil sample was left to stand
over night with 50 ml 1M HNO3 then boiled gently for 15 minutes as reported by
Haylock (1956).
1. Haylock, O.F. (1956): A Method for Estimating the Availability of Non- exchangeable Potassium th Transactions 6 International
Congress of Soil Science, 1:403-408.
DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert-1-317.pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZpszkrg_GHDA……….
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Despite the presence of a huge amount of potassium (K+) in the soil, most of the soils are
deficient in plant available K+. A large amount of the K+ is fixed by clay minerals present in
such soils and cannot be taken up by plants to achieve optimum plant growth. In such type of
soils, large amount of K+ fertilizers are required for optimum plant growth, as plants do not
respond enough to a normally recommended K+ fertilization.
Vermiculite clay minerals can fix an enormous amount of applied K+, which becomes slowly
available to the plants. The K+ dynamics in such soils are valuable to recommend K+ fertilizer
requirements for sustainable nutrient management. We analyzed the K+ dynamics of three
alluvial soils, i.e Kleinlinden, Giessen and Trebur, collected from Germany and found that the
soils with vermiculite and smectite clay minerals have more K+- fixing ability than soils
dominated by illite clay minerals. However, as the K+ concentration decreased in the soil
solution, smectite-dominant soils may easily release fixed K+ due to lower particle-charge,
whereas vermiculite and illite dominant soils may not release fixed K+ easily. Moreover,
ammonium exchangeable K+, non-exchangeable K+, total K+ and K+-fixing capacity of these
soils are directly proportional to the soil clay contents.
While recommending K+ fertilizers clay contents and the type of clay minerals is not
considered and recommended K+ fertilizers sometimes do not response plant growth
enhancement. Therefore potassium fertilizer should be recommended by taking into
consideration the type and amount of clay minerals present in the soil.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Potassium (K+) is the most abundant macro plant-nutrient in most soils. It is crucial since it
serves three important functions i.e. enzyme activation, charge balance and osmotic regulation
in higher plants (Mengel and Kirkby. 2001).
Its concentration in the earth’s crust is 2.3%, but the greatest part of this K+ is bound to primary
and secondary clay minerals, and thus not readily available for plants. Its availability to plants
depends upon the K+ concentration in the soil solution and transfer of K+ from exchangeable
and fixed form to soil solution.
The concentration of K+ in soil solution is referred to as “intensity”, whereas the soils
“capacity” is the total amount of K+ in the soil which can be taken up by plants. The transfer
rate from “capacity” to “intensity” reflects the kinetic factor of renewal of potassium (Barber,
1984).
1.
2.
Barber, S. A. 1984. Soil nutrient bioavailability: A mechanistic approach. Jhon Wiley and Sons, New
York.
Mengel, K. and E. A. Kirkby. 2001. Principles of plant nutrition. Kluwer Acad. Publishers, Dordrecht,
Boston, London.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
The major natural source of soil potassium is the weathering of K+-containing minerals such as
micas and alkali feldspars, which contain 6 - 9 and 3.5 - 12% K+, respectively. During K+
uptake, plants reduce its concentration in the immediate vicinity of roots which releases K+ions from the minerals (Kuchenbuch and Jungk, 1984).
The release of K+ converts micas to secondary 2:1 clay minerals illite and then vermiculite
(Havlin et al., 1999).
Application of K+ fertilizer to soils containing illite and vermiculite clay minerals often leads
to fixation of some of its fraction by soil particles. This fraction then becomes unavailable or
slowly available to the plants (Scott and Smith, 1987).
The fixed K+ can be made available to plants by its release from soil particles into soil solution
when the concentration of K+ is lowered in soil solution (Cox et al., 1999), but in many cases
this release is too slow to meet the plants requirement .
1. Cox, A. E., B. C. Joern, S. M. Brouder and D. Gao. 1999. Plant available potassium assesment with a modified sodium
tetraphenyle boron method. Soil. Sci. Soc. Am. J. 63:902-911.
2. Scott, A. D. and S. J. Smith. 1987. Sources, amount and forms of alkali elements in the soil. Adv. Soil Sci. 6:101-147.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Properties of different types of clay minerals developed by weathering of Mica.
(modified after Wakeel et al., 2011).
Wakeel, A., M. Farooq, M. Qadir and S. Schubert. 2011. Potassium Substitution by Sodium in Plants. Crit. Rev. Plant Sci.
4:401-413.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Determination of K+-fixing capacity of soil
Fine ground 10 g soil was shaken for 1 h on a mechanical shaker with 50 mL 0.005
M KCl in Erlenmyer flask. The sample was oven-dried at 100°C and 50 mL 1 M
NH4-acetate solution were added followed by 1 h shaking on a mechanical shaker.
After filtration through white-band 589 filter paper (Schleicher and Schuell Co.,
Dassel, Germany) the samples were analyzed for K+ concentration using atomic
absorption spectrophotometer (SpectrAA 220FS, Varian).
K+ fixing capacity was calculated by using the formula (Wakeel, 2008);
Kfix (μg /g or mg kg-1) = (9800 + Ka - Kr)/10
Where, 9800 = μg of K+ in 50 mL of 0.005 M KCl solution
Ka = Exchangeable K+
Kr = K+ concentration in soil filtrate after fixation on soil particles.
1. Wakeel, A. 2008. Substitution of Potassium by Sodium in Sugar Beet Nutrition with Special Reference to K-fixing Soils.
VVB laufersweiler Verlag, Germany.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Potassium release from the soils (Kleinlinden, Giessen and Trebur) used for soil culture
experiments. Potassium was extracted from the soils by electro-ultra-filtration (EUF) technique
and K+ concentration was measured with an atomic absorption spectrophotometer.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934
Potassium dynamics in three alluvial soils differing in clay contents
Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah.
Emir. J. Food Agric. 2013. 25 (1): 39-44
Correlation between soil clay contents and K+ concentrations in the soils. A shows correlation between soil clay
contents and ammonium exchangeable K+, B shows correlation between soil clay contents and total K+, C shows
correlation between soil clay contents and fixed K+ and D shows correlation between soil clay contents and K+-fixing
capacity of soil.
DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934