Effects of Different Slope Lengths on Runoff and Soil Sediment Yield in Yandev, Benue State, Nigeria

Abstract

This field experiment was conducted at the Akperan Orshi Polytechnic, Yandev. The site for the experiment was sandy soil with a slope of  4% and dimensions of 16m x 4m. The experimental design was a Randomized Complete Block Design (RCBD). Three treatments T₁, T₂  and T₃ of slope length 2m, 2.5m, and 3m for T₁, T₂ and T₃ respectively and were replicated four times. The treatments were carried out on  twelve sub-plots. Each sub-plot was bounded by brick walls to prevent overland flow from adjoining plots and land running into the plots.  The sub-plots had equal width measuring 1m. At the lower end of each subplot, a pit was excavated and a 40 liters plastic bucket  was inserted in each of the pits, which collected runoff and soil sediments. Runoff from each plot was collected using receiving vessels,  which were placed in the pits, dug at the end and in sloping direction of the sub-plots. A graduated 1000ml cylinder was used to measure  the runoff from the sub-plots after each rainfall. The measurement was performed by turning runoff collected in the receiving vessel into  the graduated 1000ml cylinder and then the value at the surface of the cylinder was taken at eye level, where the centre of the meniscus  shows the measurement line. The soil sediments from each sub-plot were oven dried and weighed using electronic weighing machine.  Mean runoff value for T₁  was 612.11m³ /ha, T₂  was 426.72m³ /ha and T₃ was 343.69m³ /ha while soil erosion sediment values from T₁,  T₂ and T₃ were 2.44tonnes/ha, 2.81tonnes/ha and 2.95tonnes/ha. The results implied that treatment three T₃ with slope length 3m  produced the least runoff while treatment one T₁ produced least soil erosion sediments. The results also showed that runoff decreased  with increase in slope length while soil erosion sediments increase with increase in slope length.