SOIL CHEMICAL VARIABILITY IN SANDY USTALFS IN SEMIARID NIGER, WEST AFRICA

Abstract

Extreme variability in millet [Pennisetum americanum] stands over very short distances (2 to 20 m) poses a major constraint to grain production in Niger and other Sahelian countries. This study was undertaken to examine the chemical properties of associated productive and unproductive soils. Soil samples (0 to 15 cm) were taken at 26 sites along a 15-m transect between a productive and an unproductive region in a field of the Labucheri soil series (sandy, siliceous, isohyperthermic Psammentic Paleustalf). Chemical properties of soil profiles at three locations along the transect were also examined. Unproductive soils were associated with low (< 4.5) pH, high Al + H saturation of the cation exchange sites, and decreased amounts of exchangeable K, Ca, and Mg when compared with productive sites. These chemical properties may result in Al or Mn toxicity or deficiencies of K, Ca, Mg, and P and appear to account for the variability that exists in millet stands. All soils become acidic at depths .ltoreq.30 cm. We propose a scheme for the genesis of these highly variable, acidic soils in this semiarid region.