Pedo-transfer Function of Saturated Hydraulic Conductivity and Soil Loss under Vetiver Alleys for Soil Fertility and Aggregation

The study was carried out in Runoff Research plots of Soil Science Department near Forestry Arboretum, University of Uyo, to assess the relation of saturated hydraulic conductivity to soil loss and spacing effect of vetiver alleys in controlling erosion. The experimental area of 0.24 ha on 10% slope was divided into four plots; each measuring 40 x 5 m2 with three replicates and separated by 25 cm earthen bund. After land clearing and field preparation, vetiver plantlets raised in nursery were transplanted into the field after four weeks when at least three new tillers appear. The planting of vetiver grass (VGS) was across the plots at VGS spacing of 10, 20, and 40 m intervals, while the forth plot served as control. Rainfall data were collected and soil loss and soil retained by vetiver hedges were measured using erosion pins and saturated hydraulic conductivity (Ksat) for each plot was measured by the laboratory constant head core method. Analyzed results showed that, in the month of May, average rainfall of 219.20 mm caused a mean total of 0.54 cm ha-1 of soil loss, of which only 10 m vetiver plots retained soil of about 0.03 cm ha-1, other vetiver plots including the control plots did not retain any soil. In June, 10 m plots retained 0.07 cm ha-1, whereas 20 m plots yielded 0.04 cm ha-1, and 40 m plots 0.02 cm ha-1. Ksat ranged from 5.91 to 7.33 cm hr-1 in the control plots, 7.88 to 20.15 cm hr-1 in 10 m spacing, 8.06 to 13.47 cm hr-1 in 20 m plots and from 6.93 to 7.69 cm hr-1 in the 40 m vetiver plots. Soil losses across the experimental plots were relatively high in the month of June in both vetiver and non-vetiver plots because of high intensity of rainfall (1108 mm). But the soil loss in vetiver plots was significantly lower than that of non-vetiver plots. This result proved that under vetiver soil conservation practice, the variability in the amount of Ksat might not be exclusively correlate with soil loss, but soil loss in the field increased during the precipitation of a particular day due to the antecedent moisture content with reduced 0.5 mm aggregates.