Percent Clay, Aggregate Size Distribution and Stability with Depth along a Toposequence Formed on Coastal Plain Sands

We studied the distribution of clay and its effects on aggregate size distribution and stability along a toposequence formed from coastal plain sand in a tropical ecosystem, the distribution of percent clay with depth; 0-15, 15-30, 30-45 and 45-60cm was related to changes in soil aggregation. Results showed that topo position, and depth of soil significantly alone and interactively affected percent clay distribution and soil aggregation at p< 0.01. Topo position explained about 80% of the differences in clay content at shallow soil depth (0-30cm), while deeper in the soil profile (30-60 cm) it explained between 50-70% of the differences in clay content. Topo position explained over 70% of the trend in aggregate size distribution deeper in the soil profile (30-60 cm), but contributed less than 50% in affecting the trend in aggregate size distribution at the shallow depth. The effect of topo position was higher (about 70%) in influencing aggregation at micro aggregate level (< 0.6 mm), than (50%) in the macro aggregate level (>1mm) irrespective of soil depth.