Oksida-Oksida Fe dan Al

Transkripsi

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2 Oksida-Oksida Fe dan Al - Pada tanah tua daerah tropik - Kristalin dan amorf - KTK rendah - Sering bermuatan positif Dapat melepaskan fiksasi P scr kuat melalui pertukaran anion

3 KOLOID ORGANIK Humus Susunan : C,H,O Amorf KTK tinggi (> monmorilonit) Lebih mudah hancur drp liat Sumber muatan negatif : gugus karboksil dan fenol Muatan tergantung ph

4 Negative charges on humus ENORMOUS external surface area! (but no internal surface all edges) Central unit of a humus colloid (mostly C and H)

5 Charges on soil colloids Colloid type Humus (O.M.) Silicate clays Oxides of Al and Fe Negative charge 200 cmol c /kg 100 cmol c /kg 4 cmol c /kg Positive charge 0 cmol c /kg 0 cmol c /kg 5 cmol c /kg So what will those negative charges adsorb?

6 Perbedaan Koloid Liat dan Humus KOLOID LIAT Misel tersusun dari Si, Al, O Kristalin Daya jerap kation lebih rendah Mantap KOLOID HUMUS C, H, O Amorf Daya jerap kation lebih tinggi Tidak semantap liat

7 Types of charge

8 Permanent charge Octahedral sheet neutral Net negative charge

9 ph-dependent charge: on edges H + bound tightly, so the lower the ph, the less exchange there is (i.e., lower nutrient availability) Especially important in kaolinite, humus, where no internal charge imbalance

10 Influence of ph on the CEC of smectite and humus Edge charge = Internal charge

11 Ion exchange The substitution of one ion for another on the surface or in the interstitial spaces of a crystal Anion exchange (e.g., H 2 PO 4 - for NO 3- ) Cation exchange (e.g., Ca 2+ for K + )

12 Definitions cation: An ion that carries a positive charge cation exchange: A process - cations in solution exchanged with cations on exchange sites of minerals and OM cation exchange capacity (CEC): The total amount of exchangeable cations that a particular material or soil can adsorb at a given ph

13 Controls on ion exchange Strength of adsorption -Related to hydrated ionic radius and valence -The smaller the radius and greater the valence, the more closely and strongly the ion is adsorbed. Strength valence/radius Relative concentration in soil solution

14 Cation Exchange Capacity The sum total of all exchangeable cations that a soil can adsorb cmol c = centimole of unbalanced charge Expressed in terms of positive charge adsorbed per unit mass If CEC =10 cmol c /kg soil adsorbs 10 cmol of H + can exchange it with 10 cmol K +, or 5 cmol Ca 2+ number of charges, not number of ions, what matters

15 Exchange affinity Held more strongly Held more weakly H + Al 3+ > Ca 2+ > Mg 2+ > NH 4 + = K + > Na + This is referred to as the Lyotropic series Strength of adsorption proportional to valence hydrated radius

16 Ion exchange vs. CEC Sandy loam Crystal edge Ca 2+ NO - 3 Mg 2+ Cl - H + NH + 4 K + H + VERY acidic soil H + NO 3 - HSO 4 - NO - 3 H + NO 3 - How many charges are there to fill??? CEC = 7; AEC = 2

17 Examples of cation exchange K + K + + Ca 2+ Ca K + Al K + K + K + K + + Al 3+ The interchange between a cation in solution and one on a colloid must be CHARGE balanced The reactions are reversible, unless

18 Kapasitas Tukar Kation(KTK) Banyaknya kation (dalam miliekivalen) yang dapat dijerap tanah per satuan berat tanah (100 gram) Menggambarkan kation yang dijerap + dipertukarkan antara kompleks jerapan dan larutan tanah. KTK tinggi kesuburan tinggi. KTK tinggi : 1. bila BO tinggi,2. liat tinggi Nilai KTK digunakan untuk klasifikasi tanah

19 CEC and ph high Na + binds loosely, exchanges readily CEC low 3 H + binds tightly, doesn t exchange Soil ph 8

20 Hubungan KTK - BO

21 OM has highest CEC 2:1 clays 1:1 clays Non-clayey soils

22 CEC and weathering intensity

23 Soil Order CEC (cmol c /kg) Soil order CEC Key factor Oxisols Ultisols Low 3.5 Alfisols 9.0 Mollisols 18.7 Vertisols 35.6 Histosols High Al/Fe oxides 1:1 clay Low ph 2:1 clays O.M. low high

24 Kapasitas Tukar Anion Kapasitas tukar anion (KTA) banyak ditemukan pada mineral liat amorf dan liat Al dan Fe oksida (seskuioksida) Tanah yang mempunyai muatan positif berakibat : a.terjadi penjerapan anion seperti nitrat dan klor b.kation-kation tidak dijerap oleh tanah sehingga mudah tercuci c.p dan S difiksasi sehingga menurunkan tingkat ketersediaannya

25 KEJENUHAN BASA Perbandingan antara jumlah kation basa dengan jumlah semua kation (kation basa + kation asam) Kation Basa : Ca ++, Mg ++, K +, Na + Kation Asam : H +, Al 3+ Kation basa : unsur hara yang diperlukan tanaman Tanah dengan kejenuhan basa tinggi : 1) belum tercuci, 2) subur Tanah dengan kejenuhan basa rendah : Kompleks jerapan diisi kation asam (H +, Al 3+ ) Kejenuhan basa maks pada ph netral.

26 Adsorbed cations: area Humid region soil Arid region soil H + H + NH 4 + K + H + K + Al 3+ Mg 2+ H + Ca 2+ Mg 2+ Low ph (acidic) High ph (basic)

27 Soil Order Base Saturation (%) Soil order Oxisols Base Sat Low low Ultisols <35% Alfisols Medium-High Mollisols High >50% high

28 Unsur Hara Unsur makro Diperlukan dalam jumlah banyak Unsur mikro : Diperlukan dalam jumlah sedikit

29 Mekanisme Penyerapan Hara 1.Aliran Masa Gerakan unsur hara dalam tanah menuju permukaan akar tanaman bersama-sama gerakan air. Penarik : transpirasi Perlu energi Sebagian besar unsur hara : N (98,8%), Ca (71,4%), S(95%), Mo (95,2%)

30 2. Difusi 3.Intersepsi Akar Perpindahan suatu zat (unsur hara) dari konsentrasi tinggi ke konsentrasi rendah. P (90,9%), K (77,7%) Perpanjangan akar memperpendek jarak tempuh unsur hara mendekati akar tanaman Ca (28,6%)

31 MEKANISME SERAPAN ION Absorpsi ion secara aktif A + difusi pasif AB C BC C + B -

32 MEKANISME TRANSPOR HARA DALAM TANAMAN APOPLAS SIMPLAS Ekstraseluler/transpor dinding sel Transpor dari sel ke sel melalui plasmodesmata

33 MEKANISME PELEPASAN ION KE DALAM XYLEM LEAKAGE (BOCORAN) Jaringan stele permeabel dan tidak mampu menyerap ion secara aktif SECRETED Sel parenchym memegang peran penting dalam sekresi ion

34 Faktor-Faktor yang Mempengaruhi Penyerapan Ion (Hara) Oksigen : rendah serapan rendah Temperatur Cahaya : fotosintesis serapan Q10 = 2 X Karbohidrat : rendah serapan rendah ph : rendah menguran gi serapan kation T rendah : membran fluiditas rendah/resistensi membran tinggi