Cation Exchange Capacity And Alkaline Saturation

CATION EXCHANGE CAPACITY AND ALKALINE SATURATION Cationic Exchange Capacity Soil has the ability to trap and exchange the cations it immerses, such as H+, NH4+, K+, Na+, Ca2+, Mg2+, Al3+, etc. This ability arises because soil colloids, both in the form of inorganic colloids (silicate clay minerals, Fe- and Al-hydroxide compounds, and others) and organic colloids (humus), are generally negatively charged. The negative charge in this colloid comes from isomorphic substitutions, faults at the edges of the crystal and clusters functional organic animals, such as carboxylates and phenols. Charges originating from isomorphic substitutions are permanent charges or pH-independent charges, while those originating from faults at the crystal edges and functional groups of organic organisms are pH-dependent charges. The ability of soil to capture cations is known as cation exchange capacity (KTK) and is expressed in me/100g of dry soil in a 105°C oven or cmol(+)/kg. The magnitude of the KTK depends on the density of the negative charge and the specific surface of the colloid. The higher the density of the colloidal negative charge and the greater the specific surface area of the colloid, the higher the soil KTK. Thus, fine-textured soils that are rich in organic matter will have a higher KTK than coarse-textured soils that are The organic matter is low. Base Saturation Some of the cations adsorbed by soil colloids are alkaline cations, namely Ca2+, Mg2+, K+, and Na+. The number of places occupied by these cations in the scavenger complex illustrates the saturation of the soil alkaline (KB). This alkaline saturation can be expressed as the amount of bases (me) present in 100 g of dry soil oven at 105°C (me/100g soil) or as percentage of KTK which is also called the percentage of alkaline saturation (%KB). The two statements above provide an overview of the number of bases in the adsorption complex available to plants and the nature of soil reactions. Generally, the higher the birth control, the higher the pH and soil fertility. On the other hand, the lower the KB, the lower the soil pH, because most of the adsorption complex will be occupied by H+ and Al3+ cations, as is found in acidic soils. 55 Determination of Cation Exchange Capacity and Base Saturation Basically, the determination of KTK and family planning can be divided into two stages. The first stage is to bind the attachment complex with a cation (e.g. NH4+). During the saturation process, the cations adsorbed in the soil adsorption complex are pushed out and replaced by NH4+ cations that has eclipsed the Entrep complex with other cations (e.g. Na+) so that the number of NH4+ can be determined. - K Na Ca H dll - NH4 - NH4 - NH4 - NH4 - NH4 + NH4+ + NaOH - NH4 NH4 NH4 NH4 NH4 -Na -Na -Na -Na -Na + + K+, Na+, Ca2+, Mg2+, H+, Al3+, etc. NH4OH NH4OH NH3+H2O 2 NH3 + H2SO4 (excess) (NH4)2SO4 H2SO4 + NaOH Na2SO4 + H2O (residual) How Cationic Exchange Capacity Determination works The stages of the work are as follows: 1. Weigh 5 g of 2 mm air dry soil sample and place it in a 100 ml centrifuge tube 2. Add 20 ml of NH4OAc solution N pH 7.0. Stir with a glass mixer until evenly distributed and leave for about one night 3. Stir again and then centrifuge for 10 minutes to 15 minutes at 2500 rpm 4. NH4OAc extract was approached, filtered through a sieve and filtrate was housed in a 100 ml measuring flask. 56 5. Addition of NH4OAc N pH 7.0. Repeat up to 3 more times. Each time the addition is stirred evenly, the centrifuge and the extract is deanted into a 100 ml measuring flask, after which the NH4OAc solution is added until the mark is marked. This extract is used in the determination of interchangeable levels of K, Na, Ca, Mg as well as for the determination of base saturation. 6. For washing off excess NH4+ add 20 ml of 80% alcohol to it centrifuse tubes containing the soil residue. Stir until evenly distributed, the centrifuge, decantation and filtrate are discarded. The washing of excess NH4 with alcohol is carried out until the soil in the centrifuge tube is free of NH4. This can be known by adding a few drops of Nesssler reagent to the filtrate. If there is a yellow deposit, it means that there are still NH4+ ions. 7. After being free from NH4+, the soil is quantitatively moved from centrifuge tube into boiling flask. Add about 450 ml of water. 8. In the boiling pumpkin are added a few boiling stones, 5-6 drops of liquid paraffin and 20 ml of 50% NaOH, then distilled. 9. Distillate is housed in 250 ml erlenmeyer containing 25 ml of H2SO4 0.1 N (pipetted exactly 25 ml) and 5-6 drops of Conway indicator. Distillation is stopped if the stored distillate reaches approximately 150 ml. 10. Excess acid is titrated with NaOH 0.1 N. The titration endpoint is reached when the color changes to green. 11. Perform distillation without soil as blanks. 12. The amount of KTK is calculated according to the formula: (ml blank – ml sample) x N NaOH KTK (me/100g) = x 100 soil sample weight 105°C 13. Standardize NaOH 0.1 solution N with oxalic acid as the primary standard standard using the phenolphthalein (PP) indicator: weigh x mg oxalic acid (with analytical balance) into Erlenmeyer, dissolve with aquades to taste, add the PP indicator and titrate with NaOH 0.1 N. Record the number of ml of NaOH used. How to Determine Base Saturation The stages of the work are as follows: 1. Take enough NH4OAc extract from the determination of KTK 2. Set the content of Ca and Mg with AAS, and K and Na with Flamephotometer. KB = (K + Na + Ca + Mg)/KTK x 100% 57