KAPASITAS TUKAR KATION

1. MANAJEMEN KESUBURAN TANAH KAPASITAS TUKAR KATION & HARA TANAMAN

2. Cation Exchange Capacity (CEC) Clay Particles and Humus • affect chemical properties of soil • complex structures with many negative charge sites • negative charge sites attract positive ions called cations

3. KTK = CEC Negative charge sites are referred to as . . . Cation exchange sites + attract cations from soil solution+

4. KTK = CEC Force of attraction is called: Adsorption similar to force of a magnet holding iron filings

5. ADSORPSI = JERAPAN KATION

6. KTK = CEC Cations can move on and off particles . . . when one leaves, another replaces it This process is called cation exchange, and cations involved are said to be exchangeable http://www.une.edu.au/~agronomy/SSCATXCH.dcr

7. KTK = CEC The number of sites that a colloid (small particle) of charged clay or humus (micelles) contains is measured by the: Cation Exchange Capacity expressed in mEq/100g (older unit) or cmolc/kg

8. KTK = CEC may range from: 2.0 mEq/100g for sand to > 50 mEq/100g for some clays and humus 100-300 mEq/100g under certain soil conditions

9. KTK = CEC How fertile can a soil be? Does applying more fertilizer always provide more nutrients to plants? How much of the CEC is actually filled with cations?

10. KTK = CEC The proportion of the CEC occupied by basic (+) nutrients such as Ca, Mg, K, Na, is called: Percent Base Saturation and is an indication of the potential CEC of a given soil

11. KTK = CEC Estimations that > 99% of cations in soil solution are adsorbed . . . does not mean that percent base saturation is 99%

12. KTK = CEC Example: A soil with CEC of 10 mEq/100g has 6 mEq/100g of bases (Ca, Mg, K, Na) occupying exchange sites What is the percent base saturation of the soil?

13. KTK = CEC 6 mEq/100g bases 10 mEq/100g sites = 60 % base saturation

14. KTK = CEC Cation Exchange is determined by: 1) strength of adsorption 2) law of mass

15. KTK = CEC Strength of adsorption is as follows: H+ and Al3+ > Ca2+ > Mg2+ > K+ > NH4+ > Na+

16. KTK = CEC Law of Mass the more of one ion available, the greater the chance of adsorption

17. KTK = CEC Cation Exchange Capacity (CEC) is the ability of the soil to hold onto nutrients and prevent them from leaching beyond the roots. The more cation exchange capacity a soil has, the more likely the soil will have a higher fertility level. When combined with other measures of soil fertility, CEC is a good indicator of soil quality and productivity. The cation exchange capacity of a soil is simply a measure of the quantity of sites on soil surfaces that can retain positively charged ions by electrostatic forces. Cations retained electrostatically are easily exchangeable with other cations in the soil solution and are thus readily available for plant uptake. Thus, CEC is important for maintaining adequate quantities of plant available calcium (Ca++), magnesium (Mg++) and potassium (K+) in soils. Other cations include Al+++( when pH < 5.5) , Na+, and H+. DIUNDUH DARI: http://www.swac.umn.edu/classes/soil2125/doc/s12ch2.htm ….. 17/9/2012

18. Cation exchange capacity (CEC) The capacity of a soil to adsorb and exchange cations (positively charge ions, Ca2+, Mg2+, K+, Na+, NH4+ , Al[OH]2+, Al3+, and H+). This capacity is due to the net negative charge of soil colloids (clays and organic matter) DIUNDUH DARI: http://www.swac.umn.edu/classes/soil2125/doc/s12ch2.htm ….. 17/9/2012

19. Cation Exchange Capacity (CEC) • Sources of charge on clays: • 1.Ionizeable H+ on edges (pH-dependent, similar to charge on OM), just as in the case of a weak acid. • 2.Isomorphous substitution in clays: • Substitution of Al3+ for Si4+ in the tetrahedral layer of clays • Substitution of Mg2+ for Al3+ in the octahedral layer of clay • This type of CEC is often referred to as permanent charge CEC because it is not affected by pH.

20. Cation Exchange Capacity (CEC) Sources of charge on clays: Both ionizable H+ and isomorphous substitution impart CEC to clays. Total CEC of the soil is dependent upon the amount of these sources and also upon the surface area of clays exposed (lower when they clamp shut) See swarm of cations in diffuse double layer

22. Silicate Clay Types • Amorphous silicate clays (allophane): • Mixtures of Al and Si that have not crystallized. May contain other oxides like Fe. • Often present where weathering ins not complete, as in from volcanic ash (present in Andisols) • CEC: variable to high, can have AEC (amphoteric), high affinity for P • Shrink-swell: low

23. Silicate Clay Types • Kandites (kaolinite, nacrite, halloysite): • Kaolinite is most common • Secondary mineral formed in soil; prevalent in highly-weathered soils • Structure: 1:1 , 0.7 nm spacing • Interlayer: hydrogen bonds between sheets (no water or cations) • CEC: low • Shrink-swell potential: none

24. Silicate Clay Types • Smectities (montmorillonite, saponite): • Secondary mineral formed in soil; prevalent in less highly weathered soils • Structure: 2:1 , 1-2 nm spacing • CEC: very high (highest of all clays) • Interlayer: water molecules and miscellaneous cations • Shrink-swell potential: very high

25. Silicate Clay Types • Hydrous mica and illite: • Poorly defined group, 2:1 clays • Micas: • Primary mineral (Important in igneous and metamorphic rocks) • Structure: 2:1 , 1 nm spacing • Interlayer: K+ • CEC: low • Shrink-swell potential: none

26. Silicate Clay Types • Hydrous mica and illite: • Fine-grained micas (formerly called illite): • Weathered mica (smaller particle, less interlayer K+) • Structure: 2:1, 1 nm spacing • CEC: intermediate • Interlayer: K • Shrink-swell potential: none

27. Silicate Clay Types • Vermiculite: • Secondary mineral formed in soil; prevalent in less highly weathered soils • Like fine-grained mica but no interlayer K+ • Structure: 2:1, 1.0 to 1.5 nm spacing • CEC: high • Interlayer: water molecules and miscellaneous cations, especially Mg • Shrink-swell potential: high, but less than smectite

28. Silicate Clay Types • Chlorite • Secondary mineral formed in soil • Structure: 2:1, 1.4 nm spacing • CEC: intermediate • Interlayer: Mg hydroxide octahedral sheet, firmly bonded • Shrink-swell potential: very low

29. Silicate Clay Types • Sesquioxides • Mixtures of Al, Fe oxides and hydroxides left after extensive weathering (hot humid soils - Oxisols, Ultisols) • Shrink-well: none • CEC: low, amphoteric can have AEC, high affinity for P

33. Silicate clays: permanent charge CEC Vermiculite (High CEC, Mica (Primary mineral) expands/contracts somewhat) SiO 4 Al(OH) 1.0 3 ≈1.4 nm nm K K K K K K K Ca Mg H O Ca H O 2 2 Smectite (or Montmorillonite Illite (Med. CEC) (High CEC, expands/contracts a lot) 1.0 ≈1.8 to 4.0 nm nm H+ K K K H+ H+ Ca Mg H O Ca H O 2 2 Chlorite (Low-Med CEC) Kaolinite 0.72 0.93 nm H+ bonding nm

34. KATION TUKAR The replacement of one adsorbed cation for another from solution.

35. - - - - - - A simple example: Ca2+ exchange displaces exchangeable Na+ - - - - - - ..Na+ [Ca2+] [Na+] ..Ca2+ ..Na+ [Na+] Dissolved in soil solution Negatively-charged clay 2XNa+ + Ca2+ XCa2+ + 2Na+ X = exchangeable

36. Cation Exchange Capacity (CEC) • Quantity of exchangeable cations per unit weight of soil • Strongly affect soil solution (through cation exchange) and are available to plants • Units: centimoles of charge refers to charge; so for example 1 centimole of Ca2+ has 2 centimoles of charge, whereas one centimole of K+ has 1 centimole of charge.

37. Cation Exchange Strength of cation adsorption (lyotropic series): Na+ < K+ = NH4+ < Mg2+ = Ca2+ < Aln+ < H+ Adsorption depends on charge density (charge/vol), so increases with valence and decreases with size. Not all exchangeable ions are Aln+ and H+ because mass action allows the others to be present; but at equal soil solutoinconc's, this will be the order. DIUNDUH DARI: http://www.swac.umn.edu/classes/soil2125/doc/s12ch2.htm ….. 17/9/2012

38. Note: Al3+ is a weak acid and combines with water to form various ions depending on pH: • pH < 4.5pH 4.5-6.5 (mostly monovalent form) pH 6.5-8 (gibbsite) pH 8-11 • Al(H2O)63+ <->Al(H2O)5(OH)2+ <-> Al(H2O)4(OH)2+ <-> Al(H2O)3(OH)30 <-> Al(H2O)2(OH)4- DIUNDUH DARI: http://hubcap.clemson.edu/~blpprt/acid1.html ….. 17/9/2012

39. AKSI MASA Displacement of one adsorbed/exchangeable cation by another by competition for sites when the second has a high number of ions in solution (high concentration) This is why fertilization with K, Mg and liming (Ca2+) work - they flood exchange sites and drive off other even more strongly adsorbed cations (like H+ and Al). Also, sodic soils (10-20% exchangeable Na) are cured by gypsum in the same way. Diunduh dari: http://www.fao.org/docrep/field/003/AC172E/AC172E05.htm .... 17/9/2012

40. Ca2+ Displaces Al3+ by Mass Action even though Al3+ is more strongly absorbed Ca2+ Al3+ Ca2+ Ca2+ Ca2+ Ca2+ Al3+ Ca2+ Ca2+ Ca2+ Ca2+ Al3+ Ca2+ Cation Exchange Site Ca2+ Ca2+ Ca2+ Cation Exchange Site Ca2+ Al3+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+

41. Silicate clays: permanent charge CEC Vermiculite (High CEC, Mica (Primary mineral) expands/contracts somewhat) SiO 4 Al(OH) 1.0 3 ≈1.4 nm nm K K K K K K K Ca Mg H O Ca H O 2 2 Smectite (or Montmorillonite Illite (Med. CEC) (High CEC, expands/contracts a lot) 1.0 ≈1.8 to 4.0 nm nm H+ K K K H+ H+ Ca Mg H O Ca H O 2 2 Chlorite (Low-Med CEC) Kaolinite 0.72 0.93 nm H+ bonding nm

42. HUMUS TANAH • Temporary (will ultimately decompose) • Nearly insoluble in water, but soluble in base (high pH) • Contains 30% each of proteins, lignin, complex sugars 50% C and O, 5% N • Very high CEC on a weight basis • Develops a net negative charge due to the dissociation of H+ from fenolic (-OH), carboxyl (-COOH), and phenolic ( -OH) groups as pH increases (solution H+ concentration decreases):

43. pH-dependent CEC on Organic Matter • No chargeCEC and exch. K+ (could be any cation) • R-OH0 + OH- --------> R-O-…K+ + H2O (R stands for one of the above groups) • This leaves a net negative charge on the organic colloid (R-O-) which attracts cations just as the net negative charge on an isomorphously-substituted clay does. • Organic matter is the most important source of pH-dependent CEC in soils.

44. Organic matter : pH-dependent CEC + - K OH O + OH- + H2O OH OH High pH (depronotated, Low pH, sites protonated no CEC cation exchange site)

46. Measurement of Cation Exchange Capacity (CEC) and Base Saturation (%BS) CEC is measured by applying concentrated ammonium chloride (NH4Cl) or ammonium acetate (NH4OAc) to the sample to exchange all exchangeable cations with NH4+ by mass action The extractant solution is analyzed for Ca2+, Mg2+, K+, Na+, and in some cases Al to determine what was on the exchanger. At that point, one measure of CEC can be made (see 1 below). Then the NH4+ is displaced by another cation (typically Na+ or K+ ) by mass action, and NH4+ is then measured to obtain another estimate of CEC.

47. Measurement of CEC and %BS The usual assumption is that NH4+ constitutes a negligible proportion of CEC. Exchangeable NH4+ is often measured separately using concentrated KClextractant. H+ (pH) is not measured on this extractant, either; exchangeable H+ is measured another way. Some soil scientists argue that there is no exchangeable H+ on mineral soils; all H+ that becomes absorbed onto clay minerals quickly enters the lattice structure and causes clay decomposition to hydrous oxides.

48. There are three ways to measure CEC (two from one method and one from another method): 1. Sum of cations Method: • The sum of Ca2+, Mg2+, K+, Na+, and Al after extraction with 1M NH4Cl (a neutral salt which does not buffer pH). • CEC by sum of cations, CECsum, and is measured in the first extractant in Figure 1. • In a pure clay system (no organic matter Fe, Al hydrous oxides, of allophane; i.e., no pH-dependent CEC) this represents CEC and cations on the clay minerals (permanent charge CEC).

49. Step 2. Displace exchangeable NH4+ Step 1. Displace exchangeable + + with Na or K cations with NH4+ 1 M NaCl of KCl 1 M NH Cl 4 Soil Sample Soil Sample + + + Na or K NH displaces 4 displaces exchangeable exchangeable cations + NH 4 Extractant Extractant 2+ 2+ + Analyze for Ca, K, Mg, + Analyze for NH ; this 4 + 3+ Na, and Al ; this gives gives CEC eff exchangeable cations. Sum of these cations = CEC sum - - - + 2+ 2+ - -- NH -- Ca -- Ca + -- Na -- Na - - 4 - + - 2+ 2+ -- NH -- Mg -- Mg - - -- Na -- Na + - 4 - + -- NH - - + + + + -- K -- K - -- Na -- Na - + 4 + NH + NH + + - - 4 4 - -- NH + Na -- Na -- Na - + + -- Na -- Na + 4 - - - 3+ 3+ - -- NH + -- Al -- Al -- Na -- Na + - - - 4 - -- NH + + + -- H -- H - - -- Na -- Na + - - 4 Extractant Extractant (Exchangeable (CEC ) eff Cations, CEC ) sum Figure 1. Measurement of exchangeable cations and CEC using neutral salt. (KCl)

50. 2. Effective CEC (CECeff) at existing soil pH. • This includes the permanent charge CEC plus that portion of pH-dependent CEC that is in effect at existing soil pH. • It is determined from the second extractant in Figure 1, After the 1M NH4Cl extraction, the soil is washed with ethanol to remove soluble NH4+ , and then extracted with 1M NaCl to displace the exchangeable NH4+. • The extractant is analyzed for NH4+ .