SOIL DISPERSION AND HYDRAULIC CONDUCTIVITY IN RELATION TO CLAY CONTENT, EXCHANGEABLE SODIUM PERCENTAGE AND ELECTROLYTE CONCENTRATION IN SOILS OF SOUTHEASTERN NIGERIA
The objective of the study was to investigate the influence of some soil properties on dispersion and hydraulic conductivity of soils. Twenty soil samples collected from a depth of 0-20 cm were analyzed for their physical and chemical properties. The total clay fraction (clay) of the particle size distribution ranged from 80 to 380 g/kg with a mean of 203 g/kg and a coefficient of variation (CV %) of 47.5%. Total silt was between 20 and 400 g/kg with a mean of 129g/kg and a CV of 86.9%. Water-dispersible clay (WDC) varied from 60 to 160 g/kg, with an average WDC value of 95.5g/kg and a CV of 30.1%. The values of water-dispersible silt (WDSi) ranged between 10 and 380 g/kg with a mean value of 101g/kg and a coefficient of variation of 109.7%. The electrical conductivity of the soils ranged from 16 to 22 μS/cm with a mean of 17.95 μS/cm and a coefficient of variation (CV %) of 9.30%. The exchangeable sodium percentage (ESP) of the soils varied from 0.43 to 2.76% with a mean of 1.1% and CV of 46.36%. The soil organic carbon content of the soils ranged from 0.8g/kg to 27.2g/kg. Total nitrogen content of the soils ranged from 1.0 to 3.4g/kg with a mean of 2.4g/kg and a coefficient of variation (CV %) of 20.83%. The clay dispersion ratio (CDR) of the soils varied between 0.16 and 0.92 with an average CDR of 0.58 and 46.6% coefficient of variation (CV). The total clay content (clay) had highly significant negative correlations with dispersion ratio (DR), clay dispersion ratio (CDR) and clay dispersion index (CDI) ‘r’ = – 0.84**, – 0.91** and – 0.91** respectively, but positively, it had highly significant correlations with clay flocculation index (CFI) and aggregated silt and clay (ASC) ‘r’ = 0.91** and 0.96** respectively. The total clay content correlated negatively and significantly with exchangeable sodium percentagre (ESP) ‘r’ = – 0.49*. Exchangeable sodium percentage had significant and positive correlations with exchangeable sodium (Na+), electrical conductivity (EC) and bulk density (BD) (r = 0.52*, 0.48* and 0.46* respectively). Soil organic carbon (SOC) correlated positively and significantly with hydraulic conductivity (Ksat) ‘r’ = 0.54*. Dispersion ratio (DR) positively and highly significantly correlated with CDR and CDI (r = 0.86** and 0.87**) respectively but negatively and highly significantly, it correlated with CFI and ASC (r = -0.87** and -0.93**). Clay dispersion ratio (CDR) had a positive and highly significant correlation with CDI (r = 0.99**). Water- dispersible clay (WDC) had a negative and significant correlation with BD (r = -0.53*). Water-dispersible silt (WDSi) also had a negative and significant correlation with BD (r = -0.54*). Dispersion ratio (DR) had positive and significant correlations with pH both in water and in KCl (r = 0.46* and 0.56*) respectively. The clay contents had positive and highly significant correlations with the levels of dispersion in all the soils. As the amount of 0.1N NaOH used for dispersion increased, the amount of dispersed clay increased while hydraulic conductivity of the soils decreased correspondingly.