VARIABILITY OF INFILTRATION IN THE NORTHERN GUINEA SAVANNA ALFTSOL OF NIGERIA

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Abstract:

The ring infiltrometer method was used to measure infiltration rate of a savanna soil on a 60m transect, at 2m intervals. This was done with the aim of evaluating the magnitude of spatial variation of infiltration over a field considered uniform interms of soil type. Philip and Kostiakov’s equations were employed for predicting infiltration rate of the soils in the field. Curve fitting by regression techniques showed that infiltration of the soils are adequately described by both equations (R2 > 0.98). There was relatively high variation in infiltration rate with a mean of 27.4mm/hr and a standard deviation of 15.25mm/hr. These values were also log-normally distributed. Infiltration rate was poorly correlated with bulk density (r = 0.32) and porosity (r = 0.32) but it was significantly correlated with macroporosity (r = 0.38*) at 5% level of significance. Further analysis using autocorrelograms, showed that the steadystate infiltration rates for the 30 points/locations were spatially independent at the sampling intervals of 2m. The mean and standard deviation values of saturated hydraulic conductivity were 44.78mm/hr and 3 7.27mm/hr respectively. These values gave rise to wide variation in conductivity measured between points. The variation was spatially independent with a log-normal frequency distribution. Thus, it can be unreliable to use single determined infiltration or hydraulic conductivity value as representative of the field. Due to the spatial independence of the data for these parameters, 10 and 58 samples are required to estimate the mean steady-state infiltration rate and hydraulic conductivity for the study area, respectively. These sample numbers are obtained within ± 10% of the population mean at the 95% confidence level assuming normal distribution.

VARIABILITY OF INFILTRATION IN THE NORTHERN GUINEA SAVANNA ALFTSOL OF NIGERIA

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