The fundamental environmental factor that differentiates rice cultural types that are not upland or irrigated is the depth and duration of flooding. The effect of flooding depth on plant type and growth duration is shown in Figure 9.1. After considerable deliberation, rice scientists recognized five major rice-growing environments: irrigated (subdivided by temperature regime), rain-fed lowland (by drought, submergence and waterlogging), deep water (by water depth), upland (by length of growing season) and tidal wetlands (by the presence of salinity and soil problems) (Khush, 1984). This useful and tidy classification goes a long way in clarifying many confusing concepts and terminologies of the rice environment but there remain considerable overlaps between categories — not the least in respect of water depth. As Garrity (1984) pointed out, the recognition by plant breeders of certain water depth boundaries has given rise to a bewildering array of names. This is particularly true of the critical depth range of 50–100 cm which has been variously referred to as deep, semi-deep, medium-deep, intermediate and shallow deep.
KeywordsWater Depth Floating Rice Tidal Wetland Lowland Rice Bacterial Leaf Blight
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