Soil degradative effects of slope length and tillage methods on alfisols in western Nigeria. III. Soil physical properties

Effects of six slope lengths, 60 m to 10 m with 10-m increments, on soil physical properties were evaluated for plough-based conventional till and no-till seedbed preparation on field runoff plots for three consecutive years from 1984 to 1987. Soil physical properties measured included texture, bulk density, infiltration capacity, and soil moisture retention characteristics. Conventional till treatment caused a rapid increase in soil bulk density and penetration resistance, and decrease in available water capacity and equilibrium infiltration rate. Gravel content increased with cultivation duration. Soil bulk density of 0-5 cm depth was 1.20 Mg m(-3) for 1984, 1.39 Mg m(-3) for 1985 and 1.46 Mg m(-3) for 1986 for conventional till; and 1.13 Mg m(-3) for 1984, 1.33 Mg m(-3) for 1985, and 1.27 Mg m(-3) for 1986 for the no-till treatment. The penetration resistance of the no-till treatment was relatively low and increased with cultivation duration. Mean penetration resistance for 0-5 cm depth was 2.2 kg cm(-2) in 1984, 2.71 kg cm(-2) in 1985, and 3.79 kg cm(-2) in 1986. The available water capacity decreased in both tillage methods without any consistent trends with regard to slope length. The equilibrium infiltration rate declined drastically for long slopes and conventional till methods. The data support the conclusion that these soils should be managed with short slope lengths and a no-till method of seedbed preparation. (C) 1997 John Wiley & Sons, Ltd.