In most of the tropical world cassava is grown on small plots; however, in some countries (e.g., Mexico. Brazil and Nigeria). large plantations have been started and interest in mechanization is growing. The degree of mechanization depends on the amount of land, available labour in the area and general policy regarding the use of manual labour.
The use of machinery for land preparation is preferable to manual labour to ensure the best possible seed bed for tuber development. Subsequent operations of planting. weeding, topping and harvesting can be done by hand as well as by machinery.
Labour input for the production of a hectare of cassava varies widely in different parts of the tropics. It has been estimated that in Zaire 778-830 manhours are required per hectare of cassava, including preparation of cuttings, planting, weeding and harvesting. as compared with 1 868-2206 man-hours in Uganda. In South America and the Caribbean a maximum of 494 man-hours has been estimated for the same operations. A possible reason for the higher requirements in Africa is the growing of cassava as an intercrop, with more timeconsuming operations.
The peculiar nature of the cassava crop presents a number of problems as regards mechanization, hut it has been successfully mechanized to a degree in some countries.
The following is an outline of the present use of machinery in cassava cultivation:
(a) The hoe remains the principal implement for cultivating, weeding and harvesting.
(b) Basic operations. such as ploughing and harrowing, may be done by tractor.
(c) A mechanical planter made in Brazil is in use there and in Mexico. It is a tworow planter using a tractor driver and two men on the machine to feed cuttings from the reserve bins into the rotating planting turntable. In operation, the cuttings fall in succession through a hole into a furrow opened by a simple furrower. A pair of disks throw dirt into the furrow and floats pulled by chains pack the soil over the cuttings. The planter is able to cover about 5 hectares per day.
(d) A unit for ridging and planting has been developed by modifying a ridger to work as a ridger-cum-planter and a cultivator to work as a six-row planter after the area has been ridged.
(e) A simple machine used in Mexico is a gasoline-powered table saw to prepare the cuttings for planting. The machine has the advantage of speed and regularity of produced cuttings. As compared with manual work the time saving is 3:1.
(f) It has been found to be virtually impossible to carry out the first weeding operation between the ridges with a cultivator. Mechanical weeding of the top of the ridges presents a number of difficulties.
(g) A topping machine consisting of a heavy screen mounted on the front of a tractor has been developed to push down the tops: then a rotary mower on the back of the same tractor can cut the downed top to make harvesting by hand possible. The height at which the tops are cut back can be easily regulated with any rotary mower.
(h) Cassava is not a crop that lends itself readily to mechanical harvesting because of the way the tubers grow. They may spread over I m and penetrate 50 60 cm. Careless use of machinery for harvesting can damage tubers, resulting in a darkening due to oxidation that will lower the value of the flour. However, in Mexico and Thailand, mould-board ploughs have been used to make hand harvesting less tedious. Stalks can be cut successfully by a mid-mounted mower or a topping machine, and the roots are lifted mechanically with a mid-mounted disk terracer. In Ghana, about 2000 m2 could be harvested in 21/2 hours by a tractor' whereas ordinarily 5 man-days were required A modified beet or potato harvester has been suggested for use behind the tractor, with a pulling mechanism in place of the digging shares to raise the tubers by pulling at the cut stems left after topping.