Soil quality changes under continuous cropping for seventeen seasons of an alfisol in western Nigeria

Tillage and soil management effects on soil physical and chemical qualities were monitored for eight years from 1979 through 1987 in a long-term experiment involving 17 consecutive crops of maize. Effects of no-till and plow-till methods of seedbed preparation were compared at two levels of residue management (residue removed versus residue returned) and two levels of fertilizer application (without fertilizer versus recommended fertilizer). Soil chemical quality was better for no-till compared with plow-till methods. Mean soil chemical properties of 0–5 cm depth for no-till and plow-till treatments respectively were 18·6 g kg−1 versus 12·2 g kg−1 for soil organic carbon content, 1·9 g kg−1 versus 1·1 g kg−1 for total soil nitrogen, 0·14 units yr−1 versus 0·18 units yr−1 rate of decline in soil pH, 63·1 mg kg−1 versus 31·8 mg kg−1 for Bray-P, and 6·0 cmol kg−1 versus 2·3 cmol kg−1 for Ca+2. Soil chemical quality consistently declined, although the rate of decline differed among tillage and fertilizer treatments. There were also differences in soil physical quality. Soil bulk density increased with cultivation duration in both tillage methods, and use of furadan in no-till plots drastically increased soil bulk density. Infiltration rate and soil moisture retention at all suctions was consistently more for no-till than plow-till treatments. Decline in soil quality with cultivation was reflected in decrease in crop yields.