Effect of cover crop on soil physical and chemical properties of an alfisol in the Sudan savannah of Burkina faso

Abstract

The effect of several leguminous and graminaceous cover crops on soil physical and chemical properties was studied on a moderately eroded Alfisol in the Sudan savannah of Burkina Faso during the growing seasons of 1986 and 1987. Cover crops sown in 1986 were Macroptilium artropurpureum, M. lathyroides, Vigna radiata var. radiata, Cajanus cajan, Alysicarpus vaginalis, Lablab purpureus, Psophocarpus palustris, Digitaria ciliaris, and Echinochloa colona. Maize (Zea mays), cowpea (V. unguiculata) and a bare fallow were included in the trials for comparison. After harvest of maize and cowpea, following farmer practice, crop residues were removed from the plots. Cover crop residue, however, was retained as in situ mulch. Maize was sown on all plots in 1987 following cultivation of a 0.20 m wide strip to a depth of 0.05 m within plant rows (strip tillage). No herbicide was used at any time during the trial. Soil properties measured were bulk density, water infiltration, particle size distribution, organic carbon, nitrogen, Bray‐l‐P, exchangeable Ca²⁺, Mg²⁺, Na⁺ and K⁺ total CEC, soil water potential and soil water retention at depths of 0.30 and 0.60 m, and soil temperature at a depth of 30‐mm. Apparent pore size distribution at depths of 0.30 m and 0.60 m was inferred from porosity and soil water retention characteristics. Ground cover of cover crops was measured in 1986. Root growth of cover crops in 1986 and of maize in 1987 was measured by sampling with an auger at depths of 0–0.10 m, 0.10–0.20 m, 0.20–0.30 m, 0.30–0.50 m and 0.50–0.75 m, and “washing” the samples over sieves with aperture diameters of 0.2 mm. Clay content in treatments sown to C. cajan, Z. mays, A. vaginalis and bare fallow were greatest due to loss of topsoil and exposure of the clay‐rich subsoil. Sowing of M. artropurpureum and M. lathyroides resulted in greater levels of soil organic C, C/N ratio and exchangeable K⁺, higher infiltration rates and soil matric potentials at depths of 0.30 m and 0.60 m, greater proportion of macropores (pore radius >14.3 μm) and higher subsoil root growth, grain, and dry matter yields of maize in 1987. Significant increases of the above soil properties, root growth, and yield of maize were also obtained by sowing of P. palustris, L. purpureus, and E. colona. Soil degradation was greatest where treatments in 1986 were either C. cajan or bare fallow. Sand and silt contents, exchangeable Co²⁺, Mg²⁺, and Na⁺, total CEC, soil N, Bray‐l‐P, and total porosity were not significantly affected by cover crop. Soil ameliorative ability of cover crop was primarily related to rapidity of formation of ground cover and subsoil root density. In terms of soil ameliorative abilities of the cover crops studied, M. lathyroides and M. artropurpureum were, therefore, the most appropriate for the Sudan savannah of Burkina Faso.