AGRONOMIC MODIFICATION OF COMPETITION BETWEEN CASSAVA AND PIGEONPEA IN INTERCROPPING

Cassava (Manihot esculenta Crantz) and pigeonpea (Cajanus cajan [L.] Millsp. ) are long-season crops and are highly competitive in intercropping. This work was undertaken to examine such competition, using two cassava cultivars of contrasting canopy size and pigeonpea sown at two different times at two plant densities. In all intercropping treatments, radiation interception by the combined canopy increased rapidly, and full ground cover was maintained up to pigeonpea harvest (ca 100 days). However, the proportion of ground area covered by each component species (canopy width) varied greatly among treatments. When pigeonpea was planted simultaneously with cassava, it became taller than cassava and its canopy occupied most of the cassava interrow space. When it was sown 35 days later than cassava, then cassava cultivar MCol 1468, which was tall and had a large canopy, dominated pigeonpea almost completely, whereas the smaller cultivar MAus 19 occupied up to only about half the total interrow area. Pigeonpea at high plant density (based on four rows between cassava rows) had similar height to that at low density (based on two rows), but its canopy occupied more interrow space and enhanced its competitiveness. The canopy width during the time of the complete ground cover was directly related to total dry-matter production and partial land equivalent ratio (LER) for economic yield of each component crop. However, cassava LER was more sensitive to reduced cassava canopy width than was pigeonpea LER, and higher total LER was obtained when a large cassava canopy width was maintained. It is therefore concluded that a vigorous cassava cultiva and late sowing of pigeonpea at a low density can sustain the desirable canopy width and competitiveness for high productivity of cassava/pigeonpea intercropping.