Studies on the Growth of cassava (Manihot Esculenta Crantz) for Forage and Tuber Production

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Experiments were conducted as the University Farm, Kumasi, Ghana (6O43’N, 1O36’W) on two cassava cultivation, Atra (early maturing) and Ankra (late maturing) to determine their suitability for the production of both forage and tubers. The treatments were different shoot harvest dates, harvest frequencies, as well as plant spacing. The yields, qualities and chemical composition of shoots and tubers were assessed. In experiment 1, the early-maturing, Atra, produced significantly higher petiole contents and stem crude protein contents and also leaf and tuber cyanide contents than the late-maturing, Ankra at the initial shoot harvest period. When varying periods of regrowth were allowed, the shoot produced by Ankra contained significantly higher crude protein content in petioles and stems, and cyanide content in stems than Atra. Harvesting shoots between 112 and 140 days after planting gave optimum dry leaf and petiole yields, whereas dry stem and tuber yield tended to increase up to 300 days after planting. Crude protein content in leaves, petioles and stems were higher when periods of growth or regrowth were shorter. Harvesting of shoots beyond 140, 196 and 224 day after planting gave significantly higher tuber, lower petiole and higher leaf cyanide contents respectively, whereas plants harvested before 104 days of regrowth contained significantly higher leaf cyanide content than each of the other treatments. Plants harvested after a regrowth period of 104 days produced significantly higher tuber cyanide content and the stem harvested after a regrowth of 132 days contained significantly higher cyanide levels than the remaining treatments. In experiment 2, the responses of both cultivars to the treatments imposed were similar except that, Ankra produced petioles with significantly higher crude protein content than Atra, whereas petioles and stems produced by Atra contained significantly higher amounts of cyanide than Ankra. Closer planting (30cm x 30cm and 45cm x 45cm) tended to lead to higher dry leaf and petiole yields, as were as higher leaf crude protein content, but tuber yields were lower. Wider planning produced significantly higher dry stem yields and crude protein contents in petioles and stem. Plant spacing of 45cm x 45cmm or closer produced significantly lower when spacing was 60cm x 60cm or closer. Tuber cyanide content was significantly higher when plant spacing was 75cm x 75cm or closer. These results suggested that for the production of high quality forage, a planting distance of 45cm x 45cmm would be satisfactory. In experiment 3, the two cultivars differed in their response to the frequency of leaf harvest. The leaves of Ankra contained significantly higher crude protein levels than Atra, whereas, Atra produced stems that contained significantly higher crude protein levels. Harvesting cassava shoots at 2- and 3-monthly intervals led to significantly higher dry petiole and leaf yields respectively, whereas leaf harvest at any frequency reduces dry stem and tuber yields. Higher crude protein levels in leaves, petioles and stems, as well as higher leaf cyanide levels were produced by the 2- and 3-monthly harvest interval treatment, but the cyanide contents of petioles and tubers were significantly higher in the 3-monthly harvest treatment only. The studies indicated that 2- or 3monthly harvest cycle would be suitable for continuous production of foliage but at the expense of tuber yield, so that foliage and tuber production cannot be achieve simultaneously in any of the two cultivars.
A thesis submitted to the Department of crop Science, 1988