Compaction Properties of Silty Soils in Relation to Soil Texture, Moisture Content and Organic Matter

Soil compaction is recognized as an increasingly challenging problem with regard to root growth and yield reduction in agricultural production in Thailand. The aim of this research was to study the effect of soil texture, moisture content and organic matter on the compaction properties of silty soils. Three soils with different silt contents were studied-loam, silty clay loam and silt loam. The study showed that compacting silt loam soil using the modified Proctor test resulted in a higher bulk density than from the oedometer test at 200 kPa. Statistical analysis showed that soil type and the moisture content significantly affected both the bulk density and penetration resistance. However, organic matter showed a significant effect only on the bulk density. The bulk density increased with increased moisture content. The bulk densities of compacted soils were higher in the order of loam, silt loam and silty clay loam. The penetration resistance seemed to increase with increased silt content. The differences in the bulk density and penetration resistance among these three soils decreased as the moisture content increased. Adding organic matter at 5% by weight to soils resulted in lower bulk densities of the soil using the oedometer test, with reductions of 3.9, 3.8 and 7.7% for loam, silty clay loam and silt loam, respectively. In order to avoid effects on root growth, it is recommended that machines with 200 kPa of tire contact pressure should only work in fields with a moisture content not exceeding 20.27, 18.74 and 17.88% for loam, silt loam and silty clay loam, respectively.