An experiment was carried out at Redland Bay on the south-eastern coast of Queensland (from 16/2/1991 to 27/6/1991) in an attempt to relate the performance of maize (Zea mays L.) /cowpea (Vicrna uncruiculata (L) Walp.) intercrops to radiation interception and to radiation availability to cowpea and to ascertain the effects of cowpea morphological characteristics. A quick maturing maize cultivar (DK529) and two cowpea cultivars (Red
caloona and 67233) were used. Changes in light availability to cowpea in intercrops were made by varying maize density. Three plant population densities were used: 22,000 plants ha-1, 44,000 plants ha-1 and 67, 000 plants ha-1.
Both cowpea cultivars were very vegetative and vigorous in growth with little difference in their morphological characteristics. Cowpea cultivar 1 (Red Caloona) was however a better climber and retained green leaves for a longer duration. Increasing maize plant population density effectively reduced amount of light reaching cowpea canopy. Light availability
to cowpea was reduced to a minimum of 13% and 15% in the high maize plant population density and to a minimum of 47% and 42% in the low maize plant population density in cowpea cultivar 1 and 2 respectively.
Intercropping reduced growth and yield of both cowpea cultivars through reductions in cowpea leaf area index (LAI), light interception and pod number. It also caused reductions in seed size in cowpea cultivar 2 (67233) . Increasing maize plant population density further reduced all the above parameters.
Maize growth and yield was affected by intercropping but to a lesser extent. Maize yields were reduced by 16% and 14% under cowpea cultivar 1 and cowpea cultivar 2 respectively compared to an average reduction of 68% and 82% in cowpea cultivars 1 and 2 across the 3 maize plant population density. Radiation use efficiency (RUE) of the intercrops was lower than that of maize sole crop but higher than that of cowpea sole crop. Intercropping proved to be more advantageous in the vegetative
stages of growth than in the reproductive stage except in the medium maize plant population density treatment. This was attributed to better light use efficiency in the early growth in intercrops than in sole crops which was estimated to be between 1.1 and 2.9 times higher in intercrops than in sole maize in the first 20 days after maize sowing (DAMS) . Results indicated that LAI and leaf longevity had a large effect on radiation interception and use in cowpea.
Cowpea cultivar 2 was better yielding in sole crop than cowpea cultivar 1 (954 Vs 621 Kgha-1) but was more affected by intercrop (157 Vs 186
Kgha-1) . An advantage of intercropping was only obtained in the medium maize plant population density intercrops. These were however small advantages (13% and 11% in cowpea cultivar 2 and cultivar 1 respectively).
Intercropping maize with these two cowpea cultivars would therefore be of advantage only where the interest of the farmer is in the production of maize grain and cowpea leaf, either for consumption, livestock feed or as green manure.