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Title: Improving sustainable intensification of cereal-grain legume cropping systems in the savannahs of West Africa: Quantifying residual effects of legumes on maize, enhancing P mobilization by legumes and studying long-term soil organic matter dynamics
Authors: Diels, Jan
Pypers, Pieter
Van Loon, L
Aihou, K
Dercon, G
Vanlauwe, B
Merckx, Roel
Issue Date: 2006
Publisher: International Atomic Energy Agency
Host Document: Management practices for improving sustainable crop production in tropical acid soils. Results of a coordinated research project organized by the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture pages:65-82
Abstract: Improved cereal-grain-legume systems, allowing farmers to use their land productively on a
continuous basis, are being rapidly developed and adopted by small-scale farmers in the West African
Moist Savannah. This paper summarizes work on several issues related to the improvement of
productivity and sustainability of these intensified systems. A first study looked at the sustainability of
several legume-maize cropping systems in a 5-year field trial at Sékou, Bénin. Fairly low maize yields
were found in continuous maize cropping systems (maize/maize), poor response to N fertilizer beyond
45 kg N ha-1, and no evidence that P and K were limiting crop yield. Over the last 5 years of the trial,
maize/Mucuna relay cropping gave consistently a 2000 kg ha-1 yield increase relative to maize/maize
cropping, and most of this yield gain was preserved even when Mucuna residues were removed from
the plots when planting the next year’s maize crop. Some yield gain, although far less than with
maize/Mucuna, was observed in the maize/pigeon pea system. The maize/cowpea system offered no
maize yield gain over maize/maize cropping. In a second study, enhanced isotopic methods to
determine the plant available P allowed us to test the hypothesis that certain legume accessions can
mobilize sparingly-available P. In one out of the 3 West-African Moist Savanna soils studied, we
found that cowpea could access sparingly soluble soil P that is unavailable to maize. This mobilization
of P was only observed when P deficiency occurred. These results confirm the P efficiency of some
legume genotypes, which may lead to benefits of improved P availability by the incorporation of
legumes in rotation systems. A third study, involving a 16-year continuous-cropping field experiment
in Ibadan, Nigeria, provided information on long-term changes in soil organic matter carbon (SOC)
contents in savannah soils with sandy top soil. In the control treatments with continuous maize and
cowpea cropping without trees, SOC levels dropped from the initial 15.4 Mg C ha-1 to 7.3–8.0 Mg C
ha-1 in 16 years (SOC content in 1700 Mg ha-1 equivalent soil mass). In the two continuously cropped
alley cropping systems (Leucaena and Senna), the SOC levels dropped to levels between 10.7 and
13.2 Mg C ha-1. The 13C natural abundance technique yielded useful information to test the ROTHC-
26.3 SOC model in sub-humid tropical conditions under a complex pattern of cropping systems.
Publication status: published
KU Leuven publication type: IHb
Appears in Collections:Division Soil and Water Management

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