Trop. Sci. 2003, 43, 167–169
Improving maize and cowpea seed quality
through seed processing
EA Asiedu, OA Danquah, P Adusei-Akowuah and AJG Van Gastel
Crops Research Institute, PO Box 3785, Kumasi, Ghana (wasdu_k@ghana.com)
Abstract A medium (110-day) maturing Quality Protein Maize variety and an early (60-day)
cowpea variety, were harvested, shelled/threshed and mechanically cleaned using an air-
screen cleaner, followed by a gravity separator. This gave significant increases in field
emergence, laboratory germination, pure seed and 1000-seed weight of maize and cowpea.
Germination and purity of both of the processed seeds far exceeded the Ghanaian minimum
standards.
Keywords: air-screen cleaner, gravity separator, cowpea, maize, seed quality.
Introduction
Maize and cowpea are important crops in West Africa but good grain yields are often not
achieved due to problems of seed quality and unfavourable field conditions. The use of good
quality seed with improved agronomic practices should lead to significant increases in grain
yield. This study aimed to improve seed quality in maize and cowpea through the use of an
air-screen cleaner and a gravity separator.
Materials and methods
A Quality Protein Maize variety Obatanpa (110 days to harvest maturity) and an early dark
brown cowpea cutivar Asontem (60 days to harvest maturity), the most popular varieties in
Ghana, were used at the Crops Research Institute’s (CRI’s) station at Kwadaso in the Forest
zone of Ghana. The maize was from the main 1999 season (April to August) and the cowpea
from the minor season (September to November). The maize was shelled mechanically using
an Alvan Blanche Minorette sheller and the cowpea was threshed using a Saatmeister Kurt
Pelz machine. The maize (2552 kg) and cowpea (618 kg) were separated into four compo-
nents using a Petkus K542 air-screen cleaning machine. This air-screen cleaner separates
first by an air current, which blows through the flowing seed, removing light materials
discharged through an outlet. Then there are metal screens to separate materials of different
sizes as the seeds move over them. The top screen with large round holes (11.0 mm diameter
for maize and 8.0 mm for cowpea) functioned as a scalper: extra-large seeds and broken cobs
ride over it to the side of the machine. Good seeds and small materials drop on to the bottom
screen, which has smaller round holes (7.5 mm for maize and 4.0 mm for cowpea) to allow
undersized materials, including split and shrivelled seeds, to pass to a spout while good seed
Accepted 3 December 2002