Environmental Factors

Ginger is a crop of the tropics and subtropics. For optimum growth, ginger requires high organic matter and, therefore, may exhaust soils. According to Prentice (1957), Kannan and Nair (1965), and Paulose (1973), ginger grows well in clay loam, sandy loam, sandy clay loam, red loams, and lateritic soils. The normal pH range is 6 to 6.5. Topography is not critical because the crop grows well on tablelands, slopes, and undulating sites. The depth of the soil is also not critical because the tuberous stem is borne near the soil surface. The soil, however, needs to be worked to fine tilth and should be loose and friable in texture in order to offer minimum resistance to rhizome initiation, development, and bulking. Heavy clays and coarse sand, therefore, restrict root development.

Ginger has a wide range of temperature tolerance. Evenson et al. (1978) found 25 to 30Ā°C to be optimum. The temperature is often assumed to be adequate in most parts of the ginger-growing world, although Leverington (1975) noted that fluctuating temperatures might cause chilling injury. In more practical terms, most of the tropical environments in which ginger thrives do not have drastic fluctuating temperatures. Relating the soil temperature to the corresponding air temperature effect during crop growth is recognized and will make a worthwhile study.

Ginger requires a humid environment for good crop growth. The optimum rainfall (1,500 to 3,000 mm) is of a wide range and should compose of intermittent showers between the time of sowing and sprouting (within the first 6 weeks of crop life), followed by regular (preferably evenly distributed) rainfall during crop growth and bulking (from third to seventh month). Ginger is sensitive to water logging. At crop maturity (prior to harvesting), the rains should cease. Ginger is essentially rain fed, but supplementary irrigation may be used to augment its water requirement. A prolonged or erratic dry condition during crop growth leads to small-sized rhizomes. This calls for further investigation to ascertain how much off-season watering is used to prolong the vegetative growth phase and bulking duration for increasing the yield of rhizome.

The altitude requirement for growth of ginger varies from about sea level (e.g., 4 m as in Bori Nigeria) to 122 m (Umudike) to 462 to 769 m in Jamaica (Prentice, 1959) and up to 1,500 m as in Himachal Pradesh and hill tracts of Assam and West Bengal (Kannan and Nair, 1956; and Menon, 1992). Frost is, however, detrimental to crop foliage and destroys exposed rhizomes while excessive low temperatures induce and prolong dormancy (Caiger and Buckhurst, 1993). However, information on critical limits has not been available.

Similarly, the influence of wind speed and irradiance (quantitative and qualitative) needs to be explored since results of field trials on it is scanty. Crop growth within para-rubber (Hevea braziliensis) plots providing partial shading as compared to open field cropping in Nigeria reveals that ginger prefers warm, but long sunshine days to hot and erratic and short ones. The other evidence on light effect is on flowering and anthesis relationship. (Thankama Pillai et al., 1978). Flowers start opening in the afternoon by about 3:00 P.M., or by a little after midday on bright sunny days in Nigeria (Okwuowulu, 1988a).

Land Preparation

It is normal to slash the natural vegetation and, through this operation, to collect mulch material. Ploughing follows, and, ideally, harrowing several times at 5-to-7 day intervals kills germinating weed seedlings. Rotovating may be desirable. Ginger is best sown on flat or raised beds (30 cm high); the culturally convenient length and width of plots being 25 m X 3 m, if the crop is not grown on ridges along the contour on slopy lands. Ploughing once but harrowing several times gives the most desirable tilth, which creates enough room for tuberous stem initiation and bulking.

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