Continuous cultivation of West African soils: Organic matter diminution and effects of applied lime and phosphorus

Summary

Five years of sustained cropping of cleared ferallitic and alluvial soils in Sierra Leone reduced the organic matter originally under bush of both soils by 50 per cent and the cation exchange capacities by 30 per cent. The rate of organic matter loss was sharply reduced after the 3rd year and organic matter cycling was stabilized by the 5th year. It was predicted that this equilibrium could be sustained after the 5th year provided that other factors of soil fertility have not become degraded.

Lime applied to maize on ferallitic upland soils of pH 5.3 did not affect yields. The response to applied P was direct and significant. No interactions between lime and P were observed. At pH 5.3 exchangeable A1 saturated 8 per cent of the cation exchange sites and a pH 4.4 saturated 26 per cent Soil pH and Al-saturation between these limits did not influence the maize yields or reduce the availability of applied P.

Lime applied to groundnuts on alluvial soils of pH 4.4 and Ca content of 0.2 me per 100 g soil did not influence yield or uptake of leaf P, Mn, Fe, B, Zn, Mg, K, Na, Si, and Cu but directly affected Ca uptake. Lime increased the soil pH to 5.3 at harvest, and reduced Al saturation by 65 per cent, but the effect was measurable only during the year applied.