Use of Point - Based Pedotransfer Function to Predict Field Capacity of the Soil in Nsukka Area, Southeast Nigeria.

Point-based pedotransfer functions are attractive for modelling soil water content; however, they have not been widely applied to predict field capacity (FC) of weathered tropical ultisols. Determination of field capacity at Nsukka area, was carried out using field and laboratory methods. Soils in the location were gravelly (Plots E and F) while others (Plots A, B, C and D) were deep and permeable. Core and auger samples were collected and subjected to laboratory analysis for particle size distribution, pore size distribution, bulk density, organic matter, water retention and saturated hydraulic conductivity. The results obtained revealed that the soils were dominantly loamy sand. Bulk density generally decreased with depth (Plots A, B, D and E). Pore size distribution values indicate a preponderance of micro-porosity. Organic matter was low and decreased down the profile. Hydraulic conductivity classes ranged from very slow to moderate. Laboratory estimates of field capacity at 60 cm tension were higher than the field results. The correlation coefficients indicated that the FC correlated negatively with coarse sand (p<0.05, r = -0.493) and bulk density (p<0.01, r = -0.601) and positively with fine sand (p<0.05, r = 0.529), total porosity (r = 0.611) and micro-porosity (r=0.807) at p<0.01. A predictive equation, Y = 0.538 + 0.645X (Y = field capacity, X = microporosity) was obtained. The use of this kind of PTF in estimating field capacity is valuable in developing countries where soil data of adequate quality and reasonable quantity is critically important for sustainable land management.