Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

ADDING A NEW DIMENSION TO THE IMPROVED FALLOW CONCEPT
THROUGH INDIGENOUS HERBACEOUS LEGUMES
PAUL MAPFUMO', FLORENCE MTAMBANEI\JGWE',
SHEUNESU MPEPEREKI' and KEN GILLER 2
1Department of Soil Science and Agricultural Engineering, University of Zimbabwe,
P. O. Box MP 167 Mt Pleasant, Harare, Zimbabwe 2Department of Plant Sciences,
Plant Produc'tion Systems, Wageningen University, Wageningen, The Netherlands
Abstract
Opportunities for harnessing biological nitrogen fixation of non-cultivated herbaceous legllmes in order to improve soil
productivity on smallholder farms in Zimbabwe were explored in a study initiated in Decem ber 2001. Over 30 indigenous
legume species .were jointly identified with farm ers across three agro-ecological regions, ranging from sub-humid
(800 mm annually) to semi-arid «650 mm). A ewezu Smell Technique, based on the odour released from freshly harvested
legume roots, greatly enhanced the capacity of farmers to participate in the identification process, The legume diversity
was highest in Chinyika Resettlement Area where cropping had been going jllst over 20 years. This was contran)
to the loss of diversity in old Communal Areas where dominance of clean weeding practices for over 70 years has led to
depletion of the weed seed bank. Legume contribution to the total above grollnd biomass ranged from 3% in 1-year fallows
under semi-arid conditions to 88% in afield abandoned soon after crop establishment llnder sub-humid conditions.
The latter case indicated an opportunity for manipulating legume popl/lations to increase their contribution, Overall,
total fallow productivity did not exceed 3.2 t ha- J dl/e to extreme conditions of poor soil fertility, where soils had generally