Evaluation of Infiltration Characteristics of Soils Developed on Coastal Plain Sands in Calabar Municipality Local Government Area, Cross River State, Nigeria

Abstract

Infiltration of water into the soil is an important physical process affecting the fate of water under field conditions, especially the amount of subsurface recharge and surface runoff and hence the hazard of soil erosion. The study was conducted to evaluate the infiltration models of soils developed on coastal plain sands and to select a suitable models as a basis to improve the management of the soil. A total of 16 infiltration runs were made with the double ring infiltrometer. For the purpose of getting best fitting model, the results obtained from various infiltration models were compared with observed field data. The parameters considered for best fitting of model were correlation coefficient and coefficient of variability (CV). Model-predicted cumulative infiltration consistently deviated from field-measured data, that is, the models under-predicted cumulative infiltration by several orders of magnitude for Kostiakov, Green Ampt and Philip model but the model over predicted cumulative infiltration for Horton model. The results of the soil samples analysed revealed that the mean values of 707.50, 208.13 and 84.38 gkg-1 for sand, silt and clay with the textural class of sandy loam. The bulk density, particle density and total porosity had mean values of 1.84 gcm-3, 2.44 gcm-3 and 22.56%. However, there was a fairly good agreement between mean-measured cumulative infiltration (7.30 cm/hr, CV = 32.19%); Philips (1.93 cm/hr, CV = 42.49%); Kostiakov (0.13 cm/hr, CV = 30.77%); Horton (64.49 cm/hr, CV = 22.39%) and Green Ampt model (42.04 cm/hr, CV = 0.57%) respectively. The data however showed that the correlation coefficient for Kostiakov (1.00) was best fitting in predicting the field measured data and this was closely followed by Green Ampt (0.88); while Philip’s model and Horton model showed a negative correlation (r = -0.88 and r = -0.82) with the field measured data. Conservation measures involving mulching, cover cropping and afforestation are recommended to improve the soil structure and infiltration capacity.