1). The valence of an exchangeable cation therefore determines the double layer thickness. As the M3 test is an acid extraction, it is not One of the main factors limiting agricultural production in tropical climate regions is mainly related to the presence of exchangeable aluminum (Al3+) in highly weathered acid soils. Desp ite much research since Hartwell and Pember The cations include Calcium, Magnesium, Potassium, Sodium, Hydrogen and Aluminium. In fact these cations initiate the process of particle aggregation in soil. The relationship between pH and aluminium species is depicted in Fig. Wiley Online Library. These aluminium hydrolysis products can be re-adsorbed by the clay minerals causing further hydrolysis with the release of hydrogen (H +) ions in the soil solution and thereby develops soil acidity (lower soil pH). N.B. Further, experience in other areas have shown that the aluminium saturation percent (ASP = Exchangeable aluminium/ Cation Exchange capacity x 100) increases quite dramatically once soil pH reaches a level of 6.0 and less – and in future all samples with pH (water) of 6.0 or less should have exchangeable aluminium measured. The Mehlich3 Al test has no relationship with “plant available” aluminium. The measurement of soil Aluminium (Al) using 1M KCl, which displaces the aluminium from the cation exchange sites with potassium; providing a measure of “Exchangeable Al”. As a consequence an exchangeable cation of aluminum, calcium or magnesium stays close to the clay particle and does not interfere with the cohesion between aggregated particles. 3.3 Exchangeable Cations. 14.4. testing of soil pH, exchangeable acidity and mobile aluminium (Al) status in profiles of pseudogley soils of ÿ a ak Kraljevo basin. Exchangeable hydrogen is usually under 20%. The Measurement of Exchangeable Aluminum in Soils and Clays ... Aluminum, Methods of Soil Analysis, undefined, (517-550), (1996). Lime-Aluminium- Phosphorus Interactions in Acid Soils of the Kenya Highlands ... soil chemical properties and P adsorption. soil temperature, topsoil moisture) was measured on-site using an automated weather station. A sigmoidal curve described the relationship. R. B. Grossman, C. R. Berdanier, Erosion Tolerance for Cropland: Application of the Soil Survey Data Base, Determinants of Soil Loss Tolerance, undefined, (113-130), (1982). Results Soil pH and aluminium levels Over all soil sampling depths and liming rates, soil pH was strongly (R2 = 0.73) associated with soil exchangeable Al levels (Fig. Exchangeable Aluminum As a Criterion for Liming Leached Mineral Soils ... Aluminum, Methods of Soil Analysis, undefined, (275-300), (1983). In all normal fertile soils the total exchangeable bases (Ca, Mg, K, Na) constitute about 80 to 90% of the cation adsorbing capacity. Exchangeable cations refer to the positively charged ions which are loosely attached to the edge of clay particles or organic matter in the soil. W. Van Lierop, Soil pH and Lime Requirement Determination, Soil Testing and Plant Analysis, undefined, (73-126), (1990). Soil exchangeable Al was aluminium is involved. The nature and content of exchangeable bases in a soil have an important bearing on its general properties. Wiley Online Library. 1.1 Aluminium chemistry in the soil Aluminium, bound as oxides and complex aluminosilicates, ranks third in abundance among the elements in the Earth's crust.

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