Mulching is an imperative cultural practice. The convenient mulching material usually includes wilted guinea grass (Panicum maximum) or leaves of dicotyledonous species, such as the Elizabeth weed (Chromolaena odoratum) and para-rubber (Hevea braziliensis). Wilted leaves at about 10 tons per hectare give the desirable 5 cm thick coverage at the time of planting. Mulching may be repeated with 5 t/ha mulch material, to be given immediately after the first weeding about 6 weeks from planting. Cutting or gathering enough mulching material and mulching 1 ha requires 150 workdays. The alternative mulch material (one readily available everywhere) is sawdust at a 5 cm thickness of coverage. This requires 30 t/1 ha, but this induces high carbon:nitrogen ratio (if it is not properly rotted) and makes application of more nitrogen fertilizer essential. This probably explains the high level of nitrogen fertilizer application in some ginger-growing areas.
It was already stated that ginger thrives best if the soil organic matter is high. Therefore, well-rotted dip-litter poultry manure or cow dung at 20 ts/ha easily becomes a substitute for or supplements mulching. The main advantage of the practice is the slow but lasting decay process leading to long-term release of the organic matter for the crop. Other current work, for example, the application of rotted rice mill-mud (Okwuowulu, 1988a) or white polythene beads as mulch material (Evenson et al., 1978) in garden-pot experiment, serves to reduce the adverse effect of variation in soil temperature, hence buffers the ambient seedling zone to achieve quick sprouting of ginger. Absence of mulching reduces sprouting to 30 percent or even lower. Mulching also increases the available/native organic matter content and has been demonstrated to minimize nematode infestation in Fiji (Haynes et al., 1973). Weed density is also significantly suppressed. However, the cost of the polythene beads is too high to warrant adoption of this mulching method at the present level of farming. But then, as the natural vegetation (grass or broad leaves) is becoming scarce, an attractive breakthrough in ginger production technology would be a success in the production of a ginger type (an ideotype) that will sprout whether or not the plot is mulched. An alternative is to develop a sprout-promoting treatment by application of some growth regulators. These are future imperatives for sustainable ginger agriculture.
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