A Study on some Alfisols and Ultisoles in Ustic Soil Moisture Regime, Northeast Thailand

Abstract

Alfisols and Ultisoles developed on sandy parent materials in ustic moisture regime, Northeast Thailand generally portray similar characteristics. The soils occupy similar undulating landscapes of alluvial terraces. Field morphologies of these soils are quite similar making it difficult to differentiate them effectively at higher categorical levels. These soils contain appreciable amount of sand and have a range of bulk density between 1.50-1.77 g/cc. Though base saturation in the order control section of the Alfisols is higher than 35 percent their other chemical properties indicate poor fertility status in a similar fashion with that of the Ultisols. Mineral composition of these soils consists mainly of quartz and kaolinite, but montmorillonite can dominate the clay fraction at depth. Argillic horizons of the Alfisols are generally present in the deep part of the profiles. Skeleton grains and clay bridges are predominant features in their thin section of the argillic horizons. These soils have a narrow available moisture range. Water management, fertilizer application program and suitable form of slowly released fertilizer are inevitably needed for these soils to sustain sufficient field crop production.