PERFORMANCE EVALUATIONOF A SOIL WATER CHARACTERISTICS MODEL FOR THE THREE MAJOR SOIL TYPES INNIGER STATE, NIGERIA

Abstract

ABSTRACT

Soil water characteristics are critical hydraulic properties governing soil water availability and movement in soils. Sustainable soil water conservation would not be possible without accurate knowledge of these hydraulic properties. Study of soil properties such as field capacity (FC), permanent wilting point (PWP) and hydraulic conductivity (Ks) play important roles in soil moisture retention. These parameters can be measured directly; their measurement is difficult and expensive. Thus, Saxton and RawlSoil Water Characteristics-Hydraulic Properties Calculator (SWC-HPC) model provided another alternative for estimating soil parameters from more readily available soil data. In this study, 180 soil samples were collected from three different sites locating at Minna (Ferruginous tropical soil), Badeggi (Hydromorphic soil) and Mokwa (Ferrosol) which represent the major soil types in Niger State. Laboratory values of soil water characteristics were obtained from thenineprofile pits dug at (2m x 1m x 1.5m).One bulk sample and three undisturbed soil core samples were taken at a depth of 20cm progressively down the profile to a depth of 100cm. Soil samples were analysed for percentage sand, clay, and silt, as well as organic matter, salinity and compaction which were the independent variables in the model while wilting point, field capacity, saturation point, hydraulic conductivity, bulk density and plant available moisture content were the dependent variables.The model out puts were statistically compared with observed parameters from laboratory tests using the root mean square error (RMSE), coefficient of variation (CV), modelling efficiency (EF), coefficient of residual mass (CRM) and chi-square. The model accurately predicted the observed bulk densities of the soil tested, satisfactorily simulated soil moisture content at permanent wilting point and moderately simulated plant available water. The model however poorly predicted the saturated hydraulic conductivity and soil moisture content at field capacity of the soil tested. The SWC-HPC may therefore be used only to simulate soil bulk densities; moisture status at permanent wilting point and plant available water values in the three study locations of Niger State.