Properties and aluminium saturation percentage in highland soils of Khun Wang and Inthanon areas, Chiang Mai Province

Abstract

A study on Al toxicity level and properties of highland soils in Khun Wang and Inthanon areas was conducted in 31 pedons, aiming at assessing the relationship between level of Al toxicity and soil properties in order to provide equations suitable for predicting Al saturation of studied soils. Soil pits were used for this research, which included the investigation of general environments of the areas selected. Soil samples were collected with respect to soil genetic horizon and analysed using standard procedures. Soils in both areas were formed from gneiss, granite and diorite and well developed. They had well drained feature. They had low to moderate fertility level, mostly having organic matter accumulation to great depths. The soils under native forest were composed of extractable Al and Al saturation percentage higher than did the soils used for agricultural production, particularly those under greenhouse cover where formers commonly used lime to to raise soil pH, in turn, diminished the release of Al to soil system,and bases further accumulated in the soils. Humults were found in the highest number, accouting for 24 pedons of which they can be classified into Typic Palehumults and Typic Haplohumults. They contained 52.7 and 51.6% Al saturation, respectively and these values were also higher than those obtained from other soils. The values were indicative of toxicity to growing plant, especially the ones that were not native tropical which were generally rater tolerant to Al toxicity. The equation suitable for predicting Al saturation percentage in these soils was “%Al saturation = 173.8-0.57(Extr.Ca)-0.34(Extr.Na)-0.30(Silt)+0.15(CEC by NH4OAc)-0.17(pHKCl)-0.14(Extr.Mg)0.15(pHw), R2 = 0.75”.