Some factors affecting clay dispersion and aggregate stability in selected soils of Nigeria
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Department of Soil Science, University of Nigeria, Nsukka, Nigeria
Technische Universität Muchen, Lehrstuhl für Bodenkunde, D-85350, Freising, Germany
Int. Agrophys. 2006, 20(1): 23–30
Using 22 soil samples from Nigeria, comprising Alfisols, Entisols, Inceptisols, Ultisols and Vertisols with 77- 676 g kg-1 clay, we studied the effect of various treatments on clay dispersion. Aggregate stability was evaluated by the aggregated clay (AC) index, ie clay in calgon minus clay in H2O. Treatments with H2O2 to remove organic matter (OM) showed only slightly increased clay dispersion in some soils, but it increased clay dispersion in others. Organic matter also showed low correlation with AC. Greater amount of clay was dispersed following soil treatment with sodium dithionite-citrate-bicarbonate (DCB) than with acid NH4 – oxalate (Ox). Treatment with either Na-bicarbonate (B), Na-citrate (C) or Na-citrate plus Na-bicarbonate (CB) produced clay amounts comparable to those obtained with the DCB treatment but extracted only 0.06 to 2.11% of FeD and 0.24 to 19.2% of AlD. Generally, there were no significant correlations between the amount of dispersed clay and the contents of Fe and Al obtained from soil treatments with either B, C or CB extractants. Consequently, FeD explained only 22.8% and AlD about 58.4% of variation in aggregated clay, ie DCB-clay minus H2O-clay. This suggests that the bicarbonate and citrate anions increased clay dispersion even when little or no Fe and Al was removed. That can be interpreted in such a way that any aggregation effect of Fe and Al oxides cannot be eliminated only by totally extracting them but also by removing their interaction with clay and silt particles.