Prominent characteristics, types and potential of soils under cotton cultivation in upper central plain Thailand

Study on prominent characteristics, types and potential of soils under cotton cultivation was conducted on six reprensentative soils in upper Central Plain, Thailand. Results obtained revealed that these soils are Lum Narai series, Kamphaeng Saen series in two locations: Kamphaeng Saen fine loamy variant and Kamphaeng Saen coarse loamy variant. Taxonomically, they include four Alfisols, one Mollisols and one Inceptisols. These soils occupy nearly flat to undulating terrain. Their important physical characteristics include very high silt content, shallow to very deep depending on parent materials. On local alluvium or colluvium, they are shallow to moderately deep and they are very deep if developed on riverine alluvium. Most of these soils are well drained, having loam to silty clay loam and clay texture. Their chemical characteristics include a reaction range of strongly acid to strongly alkaline and medium to high inherent fertility. Mineralo gically, illite, kaolinite and smectite are found in approximately equal amount in their clay fraction. In Mollisols and Inceptisols however smectite, is the dominant mineral. Quartz dominates their silt fraction followed by feldspar. Vital factor controlling cotton yields on these soils comprise ustic soil moisture regime, high silt content, high bulk density in horizon under plow layer, low nitrogen and being alkaline. These characteristics may induce low yield of cotton. These soils could be placed into four fertility capability classification unit Cbkd, CC'bd, Ld and Ldk. They are suited for upland crops, poorly suited to generally not suited for paddy rice, well to moderately well suited for fruit trees and well suited for permanent pasture development. Recommendation on management of these soils includes organic matter management to improve their structure and to increase nitrogen, especially for the soil that has high clay content. Consideration on forms and types of fertilizer is needed on alkaline soils. In addition, phosphorus, potassium and micronutrient are necessary in some of these soils.