The effect of plant density and relative time of planting on colocasia/rice intercropping system

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Three experiments were carried out to ascertain the sustainability and feasibility of Colocasia/rice intercropping systems in a valley bottom at Jamasi in the Ashanti region of Ghana, from April 2001 to December 2002. A randomized complete block design was used in all the three experiments. The first experiment involved 6 treatments with 3 replications. The treatments comprised of 4 spacings of Colocasia (30 x 30cm, 30 x 60cm, 50 x and 60 x 60cm), sole Colocasia (30 x 60cm) and sole rice (20 x 20cm). Experiments 2 and 3 involved the time of introduction of Colocasia into rice, and rice into Colocasia, respectively. Colocasia spacing of 30 x 30cm was used in a constant spacing of 20 x 20cm for rice. The rice variety TO X 3 108-56-4-2-2-2 referred to as “sika-mo” and Colocasia esculenta var esculenta were used for the experiment. Soil samples top (0-15 cm) and subsoils (15-30 cm) were taken from plots before and after the experiments to determine the effect of the system on soil fertility. Normal husbandry practices were undertaken. Statistical analysis of all parameters was by the Analysis of Variance. Treatment differences were determined by the Least Significant Difference (LSD). Count data and yield data were transformed by the square root and log transformation, respectively. Parameters measured in rice were Leaf Area Index (LAI), plant height at harvest, shoot dry weight, number of tillers, panicle length, panicle weight, number of spikelets/panicle thousand seed weight and grain yields. In Colocasia, parameters measured were; plant height, canopy spread, number of leaves, mean tuber weight, total fresh corm weight, fresh shoot weight, number and weights of cormels and total biomass weight. In Experiment 1, results indicated that varying the spacings of Colocasia did not significantly affect performance of rice and Colocasia. Mean tuber weight was, however, higher in the widest spaced plants (60 x 60cm) and lowest in the closest spaced plants (30 x 30cm) of Colocasia. Land Equivalent Ratios (LERs) calculated to determine the most appropriate planting density for the system indicated that Colocasia should be planted at the spacing of 30 x 30cm in its intercrop with rice to give the best land use efficiency. The two close spacings (30 x 30cm and 30 x 60cm) were supplementary in effect whilst the 2 wider spacings (50 x 50cm and 60 x 60cm) were competitive in effect. In Experiment 2, results showed that when Colocasia was introduced into rice a month or 2 weeks after rice, plant height, LAI, shoot dry weight, number of productive tillers were significantly higher than when the plants were introduced simultaneously with rice. Significant differences were, however, not recorded between treatments for panicle length, weight and number of spikelets/panicle. In terms of grain yield, highly significant differences were observed between treatments. Ratooned rice crop in Experiment 2 showed that LAI, number of productive tillers and grain yield were highest when rice was established 4 weeks before planting of Colocasia and least when established simultaneously with Colocasia. In Experiment 3, the adverse effect of inappropriate relative time of intercropping was shown when rice was introduced into Colocasia fields at 3 different times. Plant height, LAI, shoot dry weight, number of productive tillers, panicle length and weight, number of spikelets/panicle and grain yield showed no significant differences among treatments, but were adversely affected by the broad leaves of Colocasia. In the ratoon crop, however, LAJ, number of productive tillers and grain yield had the highest values when introduced simultaneously with Colocasia whilst values were lowest for those established a month after Colocasia. Ratoon crop grain yields were even higher for crops established simultaneously or 2 weeks after Colocasia than for the main crop. The experiments indicated that intercropping system involving Colocasia and rice is appropriate because the two crops thrive best under similar edaphic conditions and the advantages associated are many.
A thesis submitted to the Department of Crop Science, College of Agriculture and Natural Resources in partial fulfilment of the requirements for the degree of Master of Science, 2004