Soil Sorption Properties Ability of soil to bind various substances from the dispersion medium Polydisperse system is a mixture of particles of various shapes and sizes mixed with organic substances Coarse Dispersion Colloidal Dispersion Molecular Dispersion > 2 (1)  m (> m) 2 (1)  m – 1nm (10 -6 – m) < 1nm < m

Soil Colloids Mineral Colloids –C–Clay minerals –P–Primary silicates –I–Insoluble phosphates of Al, Fe –P–Polymeric silicic acids (H 2 SiO 3 ) –H–Hydrated oxides (Al, Fe, Mn), sesquioxides Organic Colloids –H–Humic substances –P–Protein, lignin Combined Colloids – Organo-mineral complexes

Electronegative – ACIDOIDS –N–Negatively charged –A–Adsorption of cations –(–(Clay minerals, humic substances, H 2 SiO 3 ) → most of the soil colloids Electropositive – BASOIDS –P–Positively charged –A–Adsorption of anions –(–(hydrates of sesquioxides) Ampholyte – AMPHOLYTOIDES –(–(hydrated polymers of sesquioxides)

Permanent –i–isomorphic substitutions in the crystal lattice of clay minerals –O–Octahedron : Al 3+ → Fe 2+, Tetrahedron: Si 4+ → Al 3+ Variable –p–pH-dependent charge –I–Is formed by the dissociation of carboxyl groups –n–negative charge increases with increasing of soil pH Origin of Soil Colloid Charge

Soil Sorption Complexes – mineral, organic, organo-mineral C.E.C.- (Cation Exchange Capacity) (amount of cations which a soil is able to attract at pH 7, or another suitable pH) –E–Effective (how much available binding sites the soil provides at the given pH) –P–Potential (The highest C.E.C. value which soil can achieve due to pH increase) Soil Sorption Complexes

K+K+ Na + Mg 2+ Ca 2 + H+H+ H+H+ Al 3+ Acid Cations Base Cations Soil Sorption Complexes H+H+

The diverse range of methods Index Ion Method (The sorption complex is saturated by the index ions → index ions are displaced and their concentration is determined) –S–Saturation of sorption complex by index ion –W–Washing of excess ions –D–Displacing of index ion and its determination Mehlich method Bower method Methods for C.E.C. Determination

Bower Determination using AAS washing K+K+ Ca 2+ Mg 2+ H+H+ + CH 3 COONa Na + + CH 3 COOH CH 3 COOK CH 3 COONa (CH 3 COO) 2 Ca + CH 3 COONH 4 NH 4 + C 2 H 5 OH + CH 3 COONa CH 3 COONH 4 Ca 2+ Na + (CH 3 COO) 2 Mg

Methodology Weight 2g of soil 1. Step - Saturation (3x) 2. Step - Washing (3x) 3. Step – Displacement of index ions (3x) 4. Complete filtrate in the volumetric flask by 1M CH 3 COONH 4 5. Measurement of index ion concentration using AAS Add 10ml of 1M CH 3 COONH 4 Let shake for 3 min Centrifuged Add 10ml of 1M CH 3 COONa (use pipette) Let shake for 3 min Centrifuged Empty supernatant from the cuvette into waste 1. Add10ml of 95% C 2 H 5 OH Let shake for 3 min Centrifuged Empty supernatant from the cuvette into waste 2. FILTRATE SUPPERNATANT into 50 ml volumetric flask 3.

Calculation C Na ……Concentration of Na ions (mmol/ml) V……… Volume of the volumetric flask (ml) n……… Weight of soil used for the analyses (2g) mmol(+)/100g

Evaluation C.E.C.mmol(+)/100g Sorption Complex V (%) Very high  30 Fully saturated 100 – 90 High30 – 25Saturated90 – 75 Upper middle24 – 18 Low saturated 75 – 50 Lower middle17 – 13Unsaturated50 – 30 Low12 – 8 Extremely unsaturated  30 Very low  8

C.E.C. Soil TextureC.E.C. mmol(+)/100g Sand2 – 10 Loam20 – 30 Clay40 – 50 Organic SoilUp to 150