Sesquioxides, Organic Matter and Aggregation of Some Soils Modified by Termites and Earthworms.

We investigated the roles of sesquioxides and organic matter in the aggregation of soils modified by termites genera Macrotermes and Cubitermes and earthworms (Hyperiodrilus africanus) as well as topsoil. Forty samples collected from ten locations from southeatern Nigeria were used for the study. Four pretreatment techniques were employed to test the roles of sesquioxides and organic matter in the aggregation of the soils. The techniques included treatment with water alone, treatment with calgon, treatment with hydrogen peroxide + calgon and treatment with Dithionite-Citrate-Bicarbonate + calgon. Removal of organic matter and sesquioxides gave significantly (P<0.05) higher clay but significantly lower silt and sand contents relative to the calgon dispersed soil materials. Sesquioxide contents were not statistically different between modified and non-modified soils. Organic carbon varied significantly (P<0.05) among the soil materials, being higher in worm casts and Cubitermes mound, relative to top soils and Macrotermes mound. Oxalate extractable Fe was significantly lower in Macrotermes mound relative to the other modified soil. Amorphous Fe₂O₃ correlated positively and significantly (r = 0.81*) with Dispersion ratio.  DCB Fe correlated positively and significantly (r = 0.83*) with Ca content in Cubitermes mound and positively and significantly (r = 0.67*) with silt content in topsoil. The crystalline form of Fe also correlated positively and significantly (r = 0.83**) with clay but negatively and significantly (r = 0.71*) with sand in Macrotermes mounds.  Amorphous form of Fe correlated positively and significantly with silt (r = 0.34*) and with organic carbon (r = 0.38*).  These results suggest that different forms of sesquioxides are associated with different soil properties in different soil materials. The results further suggest that other cementing agents apart from sesquioxides and organic matter are associated with stability of termite mound and earthworm casts.