LONG-TERM EFFECTS OF CROPPING SYSTEMS AND FERTILIZATION ON CROP PRODUCTION, SOIL CHARACTERISTICS AND NITROGEN CYCLING IN THE GUINEAN AND SUDANIAN SAVANNAH ZONES OF BURKINA FASO (WEST AFRICA)

摘要

The long-term effects of annual fallow and two grain legumes, namely groundnut (Arachis hypogea) and cowpea (Vigna unguiculata) on soil N, fertilizer N recovery and yield of subsequent non-fixing crops were investigated in two ecological savannah zones of West Africa. The effects of fallow and groundnut on sorghum (Sorghum bicolour) and cotton (Gossypium sp) were studied using a 10-years (1993-2003) field experiment at the agronomic research station of Farako-Ba (4° 20′ West, 11° 6′ North and 405 m altitude) in Guinean savannah zone Burkina Faso. A factorial 3x8 design in a split plot arrangement was used. Three crop rotations (cotton-groundnut-Sorghum, fallow-sorghum and mono cropping of sorghum) were used as first factor and 8 fertilizer treatments (mineral NPK fertilizer, NPK+crop residues, NPK+dolomite, PK+crop residues, PK+manure, PK+compost, PK and control) were applied as second factor. In the Sudanian savannah zone, a 5-year (1995-1999) field experiment was laid down at the research station of Kouare (11° 59′ North, 0° 19′ West and 850 m altitude). A factorial of three cropping systems (cowpea-sorghum, fallow-sorghum and mono cropping of sorghum) as a first factor and 4 fertilizer treatments (mineral NPK fertilizer, NPK+dolomite, PK+manure and a control) as a second factor in a split plot design was used. In the Guinean savannah zone, grain yields of succeeding sorghum increased from 547 kg ha~(-1) in continuous sorghum to 912 and 1021 kg ha~(-10) in fallow-sorghum and cotton-groundnut-sorghum rotations respectively. Soils of fallow-sorghum and cotton-groundnut-sorghum rotations contained more mineral N at sowing. The N fertilizer use efficiency increased from 19% for the continuous sorghum to 32 and 51% for the fallow-sorgum and cotton-groundnut-sorghum respectively. Soil organic carbon increased from 0.36% in continuous sorghum to 0.39 and 0.54% in cotton-groundnut-sorghum and fallow-sorghum rotations respectively. Compared to the original soil, continuous sorghum and cotton-groundnut-sorghum rotations decreased soil organic carbon. Only fallow-sorghum rotation maintained soil organic carbon, exchange acidity and base saturation at same levels like those of original soil. Manure applications increased soil organic carbon, total N and available P. Except for the fallow-sorghum rotation, other rotations increased aluminum saturation and decreased soil pH compared to original soil. Manure or dolomite applications decreased exchange acidity and maintained soil pH and base saturation at same levels like those of original soil.