CASSAVA LEGUME INTERCROPPING WITH CONTRASTING CASSAVA CULTIVARS .1. COMPETITION BETWEEN COMPONENT CROPS UNDER 3 INTERCROPPING CONDITIONS

Seven contrasting cassava cultivars were grown in sole-cropping and in intercropping with soybean and with pigeonpea to examine how associated crop species affect the performance of intercropping. In cassava/pigeonpea intercropping, time of pigeonpea sowing and plant density were altered in two experiments. In Experiment 1, four rows of pigeonpea were sown between cassava rows at cassava planting. In Experiment 2, two rows of pigeonpea or soybean were sown at 35 days after cassava planting. In Experiment 1, cassava emerged later than pigeonpea. Canopy width of cassava did not increase once the cassava interrow was occupied by pigeonpea. Total dry-matter production of all cassava cultivars was severely affected in intercropping by the time of pigeonpea harvest. Subsequent recovery was slow and final tuber yield in all cultivars was less than 25% of the corresponding yield in solecrop. When the competitive ability of pigeonpea was reduced in Experiment 2, only a short cassava cultivar was affected severely by pigeonpea, and its recovery was poor after pigeonpea harvest. Tall cultivars gradually became much taller than pigeonpea, and in most cultivars tuber yields were reduced by only up to 30%. However, the pigeonpea was almost completely suppressed by these cassava cultivars, and its seed yield was very poor. Total solar radiation intercepted by the two species combined in intercropping was similar to that of sole cassava, but combined biomass production of the two species was lower. Harvest index of cassava cultivars was also reduced slightly by intercropped pigeonpea. It was concluded that the two species competed with each other for too long, and there was yield loss of cassava/pigeonpea intercropping over sole-cropping with any cassava cultivars, except one (MCol 1468) which was strongly competitive and produced a full cassava yield in intercropping. The soybean cultivar used in Experiment 2 was short-statured and quick maturing, and had little adverse effect on growth and tuber yield of any cassava cultivar. Radiation available to the soybean, and hence soybean growth and seed yield, was greatly reduced by tall cassava cultivars. Short or compact cassava cultivars, on the other hand, affected growth of soybean less severely, and in some cases their tuber yield was increased by the associated soybean.