BAHAN KAJIAN MK. DASAR ILMU TANAH K - TANAH Diabstraksikan oleh : smno.Jurstnhfpub.2012

BAHAN KAJIAN MK. DASAR ILMU TANAH

K - TANAH Diabstraksikan oleh:

smno.Jurstnhfpub.2012

KALIUM TANAH

Jumlah K-tanahLithosfer mengandung 2.6% KTanah mengandung <0.1 - > 3%, rata-rata sekitar 1% KTanah lapisan olah (setebal 20 cm) mengandung <3000 - >100.000 kg K/haSekitar 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 & strukturFeldspar adalah aluminosilikat , formulanya KAlSi3O8, kandungan kaliumnya 14%.Di alam, sebagian kalium digantikan oleh Na dan CaKation pusat Si4+ sebagian digantikan oleh Al3+, satu penggantian untuk setiap empat tetrahedra, sehingga menjadi

AlSi3O8-

Polimorf dari feldspar Ortoklas: monoklinik - prismatik, dlm batuan plutonikSanidin : Monoklinik, dalam batuan vulkanikMicrocline : Triklinik, mengandung magmatit-pegmatitAnortoklas : Substituted feldspar, (K,Na)AlSi3O8Nepheline : Mengandung lebih banyak Na dp KPlagioklas : (Ca, Na feldspar) mengandung sedikit kalium

Pelapukan Mineral Kalium

Proses pelapukan fisik menghancurkan batuan induk, sedangkan pelapukan kimia akan melepaskan ion K+ dari mineralTemperatur penting untuk pelapukan fisika, sedang hidrolisis penting untuk kimiawiAsam-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-tanahMineral primer yang mengandung kalium:1. Feldspar kalium : KAlSi3O82. Muskovit : H2KAl3(SiO4)33. Biotit : (H,K)2(Mg,Fe)2Al2(SiO4)3

Mineral sekunder:1. Illit atau hidrous mika2. Vermikulit3. Khlorit4. Mineral tipe campuran

Proses pelapukan mineral

KAlSi3O8 + HOH KOH + HAlSi3O8

K+ + OH-

K

Ca K+, Ca++, H+ (larutan tanah)

Koloid liat H

Pelapukan Mineral

KALIUM

Pelapukan 1. Proses fisika: Penghancuran fisik, ukuran partikel

menjadi lebih halus, luas permukaannya menjadi lebih besar

2. Proses kimiawi: Hidrolisis, Protolisis (Asidolisis)

Proses Hidrolisis dan Protolisis

KAlSi3O8 + HOH HAlSi3O8 + K+ + OH- (cepat)

HAlSi3O8 + 4 HOH Al(OH)3 + 3 H2SiO3 (lambat)

Si-O-Al + H2O + H+ Si-O + Al-OH2 + K+

K 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 Sanidine2. Na content of crystals. Anortoklas lebih mudah lapuk daripada ortoklas3. Si content. Feldspar-substitusi lebih mudah lapuk dp Feldspar4. 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 tinggi2. Solution volume. Kondisi basah mempercepat proses pelapukan3. Migration of weathering products. Proses pelapukan akan terhambat kalau hasil-hasil pelapukan terakumulasi di tempat4. The formation of difficult soluble products of hydrolysis. Kalau hasil reaksi hidrolisis mengendap maka reaksi akan dipercepat5. pH value. Semakin banyak ion H+, proses protolisis semakin intensif.6. The presence of chelating agents.

MASALAH KALIUM TANAH

Ketersediaan K-tanahTanah mineral umumnya berkadar kalium total tinggi, kisarannya 40 - 60 ribu kg K2O setiap HLOSebagian besar kalium ini terikat kuat dan agak sukar tersedia bagi tanaman

Kehilangan akibat PencucianSejumlah besar kalium hilang karena pencucian :Tercuci dari tnh lempung berdebu 20 kg K2O/ha/thnDiangkut /dipanen oleh tanaman 60 -”-

Konsumsi berlebihan: Luxury consumptionTanaman dpt menyerap kalium jauh lebih banyak dari jumlah yg diperlukanPemupukan kalium harus dilakukan secara bertahap

Masalah Kalium tanah: 1. Pd saat tertentu sebagian besar K-tanah tidak tersedia2. K-tanah peka terhadap pengaruh pencucian3. Kalium dapat diserap tanaman dlm jumlah banyak, melebihi kebutuhan optimalnya

Kadar K-tanaman

(Tinggi)

Kadar K-tanaman

K diperlukan untuk Pemakaian berlebihan pertumbuhan optimum

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 tersediaK 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 primermis. Muskovit

K dalam tanaman

K dalam mineral sekunder mis. Kaolinit

K dalam larutan tnh

K dalam PUPUK

Pelarutan pupuk

Absorpsi K

Pelepasan Kdd

atau K-terfiksasi

Adsorpsi atau Fiksasi K

Pelepasan K

Fiksasi K pd mineral primer

Transisi mine-ral sekunder menjadi mika akibat fiksasi K

Pelepasan K mengakibatkan pembentukan min. sekunder

THE POTASSIUM CYCLE IN SOILS.

DIUNDUH DARI: ………http://www.ipipotash.org/en/eifc/2011/29/3/English#fig1.

Potassium availability to plants in soil is governed by the transfer between four main

pools in the soil: structural, fixed (non-exchangeable), 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.

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 berpasir4.0

3.0

2.0

Tanah liat1.0

10 50 100

K dapat ditukar, mg K / 100 g tanah

FIKSASI KALIUM TANAH

Faktor yg mempengaruhi fiksasi K-tanah1. Sifat koloid tanah2. Pembasahan dan pengeringan tanah3. Pembekuan dan pencairan tanah4. 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

K - tersedia

Terangkut tanaman

Hilang pencucian

Hilang Erosi & Run-off

Fiksasi Kalium

Sisa tanaman & Pupuk kandang

Pupuk buatan

Mineral kalium lambat tersedia

SIKLUS KALIUM

DIUNDUH DARI: ………. https://dl.sciencesocieties.org/images/publications/books/acsesspublicati/soilmanagementb/79.fig1.jpeg

Soil Management: Building a Stable Base for AgricultureJerry L. Hatfield and Thomas J. Sauer (ed.). ISBN: 978-0-89118-195-8. Published: 2011

Faktor Ketersediaan K-

tanah

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 lain3. Mass flow dan Difusi4. Kapasitas dan Intensitas5. Mineral Tanah: Mineral Primer dan Mineral Liat

a. Kadar K mineral primerb. Kecepatan pelepasan K+ dari mineral primerc. Jumlah mineral liatd. tipe mineral liat

6. Bahan Organik Tanah7. pH tanah8. Aerasi

9. Lengas TanahDifusi K+ dalam tanah terjadi melalui dua cara, yaitu:

1. Ruang pori yang berisi air, dan2. 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-releasedpH: 3.50

Pupuk 100 kg K/ha 0.0 pH: 4.35

Tanpa pupuk K pH: 7.00 Dosis kapur, CaCO3 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 0.6 0.8K- larutan tanah ( me K / l)

Sumber: Nemeth dan Forster (1976)

Laju Penyerapan K

vs Konsentrasi K+

larutan

Laju penyerapan K+ , mole/g/jam (akar tanaman barley)

10.0

0.05 0.10 0.15 0.20 Konsentrasi K+ larutan tanah ( mM)

Sumber: Epstein (1972)

Serapan K vs

Dry matter production

Growth & nutrient uptake, %

100 silkingtasseling

Biji

dry matter

Tongkol Kalium

Batang

Daun 25 50 75 100

days after emergenceSumber: Nelson (1968)

Relationship between soil available K and response of rapeseed to K application

DIUNDUH DARI: ………. http://www.ipipotash.org/en/eifc/2010/23/4

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.

Determination of soil available K critical level. Relationship between relative rapeseed

yield and soil available K level.

Kandungan K-tanah

vs Respon pupuk

K

H

Tambahan hasil jagung , bu/ac

25Kdd = 50 ppm

Kdd = 100 ppm

Kdd = 150 ppm

Kdd = 200 ppm

25 50 75 100 125 Dosis pupuk K ( lb / ac )

Sumber: Hanway et al. (1962)

Kandungan K-daun

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 %KDefisien tanpa gejala: 0.62 - 0.91 %KNormal : 0.91 - 1.3% K

Tambahan hasil jagung , bu/ac

25Kdaun = 0.75 %

Kdaun = 1.0 %

Kdaun = 1.5 %

Kdaun = 1.75%

25 50 75 100 125 Dosis pupuk K ( lb / ac )

Sumber: Hanway et al. (1962)

Yield response to applied K

DIUNDUH DARI: ……….

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.

Relationship between grain yield to applied K and soil available K level.

Potassium in Soils

DIUNDUH DARI: http://www.extension.umn.edu/distribution/cropsystems/dc6794.html……….

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.

Relationship among unavailable, slowly available, and readily available potassium in the soil-plant

system.

Readily Available Potassium :

DIUNDUH DARI: ……….

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.

slowly available K

exchangeable K

water-soluble K

Potassium in Soil

DIUNDUH DARI: http://www.smart-fertilizer.com/articles/potassium-in-soil……….

Types of Potassium in Soil:

Potassium in soil is generally classified into four types:

Unavailable PotassiumFixed potassium or Slowly Available PotassiumExchangeable potassium or Readily Available

PotassiumSoil 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.

The Potassium cycle in the soil-plant-animal system (from SYERS, 1998)

DIUNDUH DARI: http://www.ipipotash.org/presentn/aspcwdb.html……….

. Syers, J.K. (1998): Soil and plant potassium in agriculture. Proceedings No. 411, The International Fertiliser Society York, UK. 32 pp.

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

DIUNDUH DARI: ………. http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm

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

POTASSIUM AND PLANT

DIUNDUH DARI: ………. http://www.spectrumanalytic.com/support/library/ff/Alfalfa_and_Potassium.htm

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.

. Potassium Fixation and Release

DIUNDUH DARI: ………. http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm

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.

Soil Potassium and Clay Minerals

DIUNDUH DARI: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm……….

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.

Soil Potassium and Cation Exchange

DIUNDUH DARI: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm ……….

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.

POTASSIUM CYCLE

DIUNDUH DARI: ………. http://www.tankonyvtar.hu/en/tartalom/tamop425/0032_talajtan/ch09s05.html

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

Equilibrium relationships between forms of potassium in soils.

DIUNDUH DARI: ………. http://people.umass.edu/psoil120/guide/chapter7.htm

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.

THE POTASSIUM CYCLE

DIUNDUH DARI: ………. http://faculty.yc.edu/ycfaculty/ags105/week12/biogeochemical_cycles_information/biogeochemical_cycles4.html

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.

Soil PotassiumThere 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.

DIUNDUH DARI: ………. http://extension.psu.edu/cmeg/facts/agronomy-facts-14

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.

Potassium Releasing Capacity in Some Soils of Anantnag District of KashmirSubhash Chand and Tahir Ali

Universal Journal of Environmental Research and Technology. 2011 Volume 1, Issue 3: 373-375

DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert-1-3-17.pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6-

jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZps-zkrg_GHDA……….

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.





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 nonexchangeable 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.





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.

Potassium dynamics in three alluvial soils differing in clay contentsAbdul Wakeel, Mehreen Gul and Muhammad Sanaullah.

Emir. J. Food Agric. 2013. 25 (1): 39-44

DIUNDUH DARI: ………. http://ejfa.info/index.php/ejfa/article/view/15395/7934

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.


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. Barber, S. A. 1984. Soil nutrient bioavailability: A mechanistic approach. Jhon Wiley and Sons, New York.

2. Mengel, K. and E. A. Kirkby. 2001. Principles of plant nutrition. Kluwer Acad. Publishers, Dordrecht, Boston, London.


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.


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.


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 solutionKa = 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.


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.


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.

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