Particle-size distribution and free iron oxides of alluvial soils from different agro-ecological regions in Vietnam

Abstract

Sixteen profiles of alluvial soils of Vietnam were collected from different agro-ecological regions throughout the country and analyzed for particle-size distribution and free iron oxides. The results showed that alluvial soils from different agro-ecological regions/river systems had different particle-size distribution and free iron oxides contents due to differences in sediment sources. The vertical distribution of the clay content in a profile was found to be controlled by soil forming processes and/or land management and was divided into 5 patterns. Similarly, the vertical distribution of free iron oxides content in a profile reflected soil forming process and land management; and in most profiles it showed a significant linear relationship with the clay content. Many samples of alluvial soils showed the clay loss and the lower content of free iron oxides in upper horizons. This feature was the same as that observed in grey degraded soils but at the lower level. It seems that some alluvial soils in Vietnam have been degraded.