Depth of tillage and its effect on field watershed size in Ejigbo zone, Osun State, Nigeria

The study investigated effects of different depths of tillage on flow of runoff in watersheds on fields tilled and planted with maize (Zea mays) hybrids and open pollinated variety (OPV) of maize. Twelve 1 m × 1 m × 2 m pits were dug and overlaid at all sides and at its bottom with impermeable membrane to accumulate watershed’s runoff from the fields. Twelve compartmental plots of 400 m2 each comprising 2 depths of tillage (0-15 cm and 0-30 cm) and 2 varieties of maize (hybrids and open pollinated) were used. Each of the treatments was replicated thrice to make 2 × 2 × 3 factorial design. Each plot measured 4 m × 10 m at 2 m apart. Among the data collected were the volume of water accumulated in the small earthen pits dug, flow velocity (v m/s) of water in runoff channels/collectors that fed earthen pits, slopes of the collectors, cross-sectional area of collectors and wetted perimeter. Results revealed that average infiltrometer values of 15.00±0.24 mm/h and 16.50±0.40 mm/h respectively in the upper part and the lower part were recorded. The 0-15 cm depth of tillage accumulated more volume of runoff water than the 0-30 cm depth of tillage in the pits and it was 23.33% higher in the lower depth of tillage used on the field than the 0-30 cm depth of tillage. Implying that 0-30 cm tillage depth retained more water from the rainfall compare to the water retained by the 0-15 cm depth. Even though, volume of runoff water of 0-15 cm depth of tillage was higher than that of the 0-30 cm depth of tillage, 0-15 cm depth of tillage had the highest yield of maize (9.30±4.26 t ha-1)