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

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Presentasi berjudul: "BAHAN KAJIAN MK. DASAR ILMU TANAH K - TANAH Diabstraksikan oleh: smno.Jurstnhfpub.2012."— Transcript presentasi:

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

3 KALIUM TANAH Jumlah K-tanah Lithosfer mengandung 2.6% K Tanah mengandung 3%, rata-rata sekitar 1% K Tanah lapisan olah (setebal 20 cm) mengandung 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

4 KALIUM dlm FELDSPAR KIMIA & struktur Feldspar adalah aluminosilikat, formulanya KAlSi 3 O 8, 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 AlSi 3 O 8 - 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

5 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 2KAlSi3O Al2Si2O5(OH) + 2K+ + 2OH- + 4H4SiO4

6 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) 2 Al 2 (SiO 4 ) 3 Mineral sekunder: 1. Illit atau hidrous mika 2. Vermikulit 3. Khlorit 4. Mineral tipe campuran Proses pelapukan mineral KAlSi 3 O 8 + HOH KOH + HAlSi 3 O 8 K + + OH - K Ca K+, Ca++, H+ (larutan tanah) Koloid liat H

7 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 KAlSi 3 O 8 + HOH HAlSi 3 O 8 + K + + OH - (cepat) HAlSi3O8 + 4 HOH Al(OH) H 2 SiO 3 (lambat)  Si-O-Al  + H2O + H +  Si-O +  Al-OH 2 + K + K H Pelapukan Ortoklas: 3 KAlSi 3 O H 2 O + 2H + KAlSi 3 O 6.Al 2 O 4 (OH) 2 + 2K + +6H 4 SiO 4 H2O 2 KAlSi 3 O 8 Al2Si 2 O 5 (OH) + 2K + + 2OH H 4 SiO 4

8 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.

9 MASALAH KALIUM TANAH Ketersediaan K-tanah Tanah mineral umumnya berkadar kalium total tinggi, kisarannya 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 berdebu20 kg K2O/ha/thn Diangkut /dipanen oleh tanaman60 -”- 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

10 Kadar K-tanaman (Tinggi) Kadar K-tanaman K diperlukan untukPemakaian berlebihan pertumbuhan optimum Kalium yg diperlukan (Rendah) Rendah K-tersedia dalam tanah Tinggi

11 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 ( % dari K-total) K tidak dapat ditukar K dapat ditukar K dalam larutan tnh

12 LOKASI DAN JALUR KALIUM DLM TANAH K dalam mineral primer mis. Muskovit K dalam tanaman K dalam mineral sekunder mis. Kaolinit K dalam larutan tnh K dalam PUPUK Pelarutan pupuk Absorpsi K Pelepasan K dd 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

13 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 percent of the total soil K. 1.Römheld, V., and E.A. Kirkby Research on Potassium in Agriculture: Needs and Prospects. Plant and Soil 335:

14 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 Biotite Illite Muscovite Ortoklas cropping periode, (0-15) days Sumber: Verma (1963)

15 Konsentrasi K-larutan tanah vs K dd K-larutan tanah (me/l) 5.0 Tanah berpasir Tanah liat K dapat ditukar, mg K / 100 g tanah

16 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

17 K - tersedia Terangkut tanaman Hilang pencucian Hilang Erosi & Run-off Fiksasi Kalium Sisa tanaman & Pupuk kandang Pupuk buatan Mineral kalium lambat tersedia

18 SIKLUS KALIUM DIUNDUH DARI: ………. https://dl.sciencesocieties.org/images/publications/books/acsesspublicati/soilmanagementb/79.fig1.jpeg Soil Management: Building a Stable Base for Agriculture Jerry L. Hatfield and Thomas J. Sauer (ed.). ISBN: Published: 2011

19 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 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.

20 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 Al dd, shg membuka peluang terjadinya fiksasi K+ Fiksasi K+ K-released pH: 3.50 Pupuk 100 kg K/ha 0.0pH: 4.35 Tanpa pupuk KpH: 7.00 Dosis kapur, CaCO3 K-adsorbed Pencucian

21 Efek Pupuk K terhadap K-tanah K-larutan tanah pH: 4.1 pH: 5.1 pH: 6.5 pH: 7.0 Dosis pupuk K

22 Lengas Tanah terhadap K-tanah Serapan K tanaman jagung Pupuk Kalium: 49 mg K/100 g tnh Kadar air tanah (20-40%) Sumber: Grimme (1976)

23 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 r 2 = 0.79** K- larutan tanah ( me K / l) Sumber: Nemeth dan Forster (1976)

24 Laju Penyerapan K vs Konsentrasi K+ larutan Laju penyerapan K+, mole/g/jam (akar tanaman barley) Konsentrasi K+ larutan tanah ( mM) Sumber: Epstein (1972)

25 Serapan K vs Dry matter production Growth & nutrient uptake, % 100 silking tasseling Biji dry matter Tongkol Kalium Batang Daun days after emergence Sumber: Nelson (1968)

26 Relationship between soil available K and response of rapeseed to K application DIUNDUH DARI: ………. 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 (y 2 ) and soil available K content (x) was y 2 = ln(x) (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.

27 Kandungan K- tanah vs Respon pupuk K H Tambahan hasil jagung, bu/ac 25 K dd = 50 ppm K dd = 100 ppm K dd = 150 ppm K dd = 200 ppm Dosis pupuk K ( lb / ac ) Sumber: Hanway et al. (1962)

28 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 %K Defisien tanpa gejala: %K Normal: % K Tambahan hasil jagung, bu/ac 25 K daun = 0.75 % K daun = 1.0 % K daun = 1.5 % K daun = 1.75% Dosis pupuk K ( lb / ac ) Sumber: Hanway et al. (1962)

29 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 = ln (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.

30 Potassium in Soils DIUNDUH DARI: 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.

31 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

32 Potassium in Soil DIUNDUH DARI: 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.

33 The Potassium cycle in the soil-plant-animal system (from SYERS, 1998) DIUNDUH DARI: Syers, J.K. (1998): Soil and plant potassium in agriculture. Proceedings No. 411, The International Fertiliser Society York, UK. 32 pp.

34 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: ………. 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 loamLexington29,000 Crider silt loam Princeton (limestone) 32,600 Tilsit silt loam Princeton (sandstone) 30,000 Monongahela silt loam Berea19,000 Welston silt loam Fariston (Laurel Co.) 24,400 Bedford & Dickson silt loam Campbellsville13,000 Tilsit catena silt loam Greenville24,600 Grenada silt loamMayfield29,700

35 POTASSIUM AND PLANT DIUNDUH DARI: ………. 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.

36 . Potassium Fixation and Release DIUNDUH DARI: ………. 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.

37 Soil Potassium and Clay Minerals DIUNDUH DARI: 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.

38 Soil Potassium and Cation Exchange DIUNDUH DARI: ………. 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.

39 POTASSIUM CYCLE DIUNDUH DARI: ………. 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

40 Equilibrium relationships between forms of potassium in soils. DIUNDUH DARI: ………. 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.

41 THE POTASSIUM CYCLE DIUNDUH DARI: ………. 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.

42 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. DIUNDUH DARI: ………. 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.

43 Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir Subhash Chand and Tahir Ali Universal Journal of Environmental Research and Technology Volume 1, Issue 3: DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert 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 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.

44 Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir Subhash Chand and Tahir Ali Universal Journal of Environmental Research and Technology Volume 1, Issue 3: DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6- jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZps- zkrg_GHDA………. 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, 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: 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: Singh, R.K (1995): Potassium Fertility Characterization of Two Soils Series of Rajasthan.PhD Thesis. Rajasthan Agriculture University,Bikaner.pp 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: 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.

45 Potassium Releasing Capacity in Some Soils of Anantnag District of Kashmir Subhash Chand and Tahir Ali Universal Journal of Environmental Research and Technology Volume 1, Issue 3: DIUNDUH DARI: https://docs.google.com/viewer?a=v&q=cache:75OWrRQrA5oJ:www.environmentaljournal.org/1-3/ujert pdf+soil+poTASSIUM+ABSTRACT&hl=id&gl=id&pid=bl&srcid=ADGEESgCKC2bMVv6p1MJQo1o0dZwnJxwmHUmVcDCJjtSbVEjsNjgoQcn8n6- jg_YcHHPSuQSkAk1PZ2gYIGgXuR-nHPRmPpScBSQNSCjC40imXLYPkcvF7upPQbG46dqpEj2lH3NZwsy&sig=AHIEtbT9_AaNLelq3L8rBZps- zkrg_GHDA………. 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:

46 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. 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.

47 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. 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 Soil nutrient bioavailability: A mechanistic approach. Jhon Wiley and Sons, New York. 2.Mengel, K. and E. A. Kirkby Principles of plant nutrition. Kluwer Acad. Publishers, Dordrecht, Boston, London.

48 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. The major natural source of soil potassium is the weathering of K+-containing minerals such as micas and alkali feldspars, which contain and % 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 Plant available potassium assesment with a modified sodium tetraphenyle boron method. Soil. Sci. Soc. Am. J. 63: Scott, A. D. and S. J. Smith Sources, amount and forms of alkali elements in the soil. Adv. Soil Sci. 6:

49 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. 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 Potassium Substitution by Sodium in Plants. Crit. Rev. Plant Sci. 4:

50 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. Determination of K+-fixing capacity of soil Fine ground 10 g soil was shaken for 1 h on a mechanical shaker with 50 mL 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) = ( Ka - Kr)/10 Where, 9800 = μg of K+ in 50 mL of M KCl solution Ka = Exchangeable K+ Kr = K+ concentration in soil filtrate after fixation on soil particles. 1.Wakeel, A Substitution of Potassium by Sodium in Sugar Beet Nutrition with Special Reference to K-fixing Soils. VVB laufersweiler Verlag, Germany.

51 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. 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.

52 Potassium dynamics in three alluvial soils differing in clay contents Abdul Wakeel, Mehreen Gul and Muhammad Sanaullah. Emir. J. Food Agric (1): DIUNDUH DARI: ………. 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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