THE EFFECT OF SLOPE AND MULCH ON SPLASH EROSION IN MAKURDI, BENUE STATE, NIGERIA

Abstract

Splash erosion leads to the remover of top soil particles and nutrients needed for plant growth. There are many factors that can affect splash erosion including slope, soil surface cover, soil properties and rainfall erosivity. The effect of these factors on splash is not well understood in Makurdi area, known for farming in Nigeria. The study was designed to examine the contributions of the affectives of slope, mulch cover, soil properties and rainfall erosivity on splash detachment in Makurdi area, Nigeria. Twenty experimental plots consisting of one soil tray each were set up at the Agrometeorological station of Benue State University. Four collectors were attached to the sides of each tray to assess the effects of slope and mulch on splash detachment under natural conditions. Five trays each were fixed at 5°, 15°, 25°, and 35° slopes, four of which were mulched with groundnut, rice, grass, and soybeans residues while the fifth served as control. Hydrometer, Walkey-Black Wet-Oxidation and Core methods were used to test for soil texture, organic matter and bulk density respectively. Rainfall was measured with rain-meter and kinetic energy calculated using Hudson’s 1965 equation. Fifty-nine rainstorms from April to October, 2007 were studied. Data obtained were analyzed using descriptive statistics, multiple regressions, and t- test. Gross splash rates at control trays were 46.5, 58.5, 55.5 and 54.1 kg/m2/yr at 5°, 15°, 25° and 35° slopes respectively. The highest splash rates from groundnut residue were 11.9, 11.27, 11.09 and 12.09 kg/m2/yr at 5°, 15°, 25° and 35° slope respectively, whereas the least, from soybeans mulch were 6.9, 9.58, 9.97 and 9.99 kg/m2/yr at 5°, 15°, 25° and 35° slope respectively. Significant differences (p <0.05) were observed in quantity of splashed sediments on bare and mulched surfaces. At 25° and 35° slopes particularly, 66.0 and 75.0% respectively of sediments splashed downslope on the unmulched surfaces. A total of 1532.5 mm of annual rainfall was recorded, with 98% occurring during the fifty-nine storms studied. While the highest monthly splash was 12.68 kg/m2/yr (Control tray at 15°) and 3.6 kg/m2/yr (rice at 35°) in June (8 storms), the least was 3.7 kg/m2/yr (Control tray at 15°) and 0.27 kg/m2/yr (rice at 35°) in July (7 storms). Splashed sediments showed that 21.0 and 19.4% of silt and clay occurred at 35° downslope as against 14.0 and 7.8% of the original soil used. Splashed sand reduced from 83.6 to 61.4% at 5° slope. Slope (S), Total rainfall (TRF), total intensity (TI) and kinetic energy (KE) significantly affected splash detachment variations (p <0.05) as S, TRF and TI accounted for 70.0% of downslope splash, while S, TRF, TI and KE explained 62.0% of upslope splash. TRF, TI and KE accounted for 74.0% of total splash at control slopes. Splash significantly contributed to silt and clay soil/nutrients loss especially downslope and on unmulched surfaces. The study recommends processes of mulching and slope gradient reduction in reducing splash and soil conservation in erosion ravaged areas.

Keywords: Soil tray, Mulching, Raindrop, Downslope, Erosivity, Makurdi Word Count: 489