Trend and stability analyses of millet yields treated with fertilizer and crop residues in the Sahel

Pearl millet (Penisetum glaucum (L.) R.Br.) is a major food crop grown on impoverished sandy soils in the Sahel. A 9-year long-term study was undertaken in the Sahel to test the hypothesis that integrated use of millet crop residues retained on farm fields after harvest and mineral fertilizers results in greater and more sustainable yields and conserve soil fertility better than either the use of residue or fertilizer alone. The four treatments compared were: (1) control (crop residue removed and no fertilizer applied), (2) crop residue alone, (3) 30 kg N + 13 kg P ha(-1) (fertilizer) alone and (4) crop residue + fertilizer. Use of crop residue + fertilizer increased grain yield fourfold over the control; use of fertilizer doubled millet yield relative to the control and crop residues resulted in 1.2 times more yield than the control. Crop residues significantly improved nutrient-use efficiency of the applied fertilizer. Sustainability yield index (SYI), a measure of an upward trend in yield over time, was greatest in crop residue + fertilizer plots as are soil organic carbon, available P and pH. Stability analysis indicated that crop residue + fertilizer treatment gave in greater yields and returns over fertilizer cost in the various seasons than either crop residue or fertilizer. (C) 2002 Elsevier Science B.V. All rights reserved.