Reisbausysteme und -ökotope in Südostasien

Geowissenschaftliche Methoden in der Reisbauforschung und die Ökosysteme des Überschwemmungsreisbaus

Abstract

The systems and ecotopes of rice-cultivation show a unique verification of the principle of the ecosystem man - earth in its regional differentiation. An overview of the world's physiographically and hydrologically diverse rice cultural systems by J. C. O'Toole and T. T. Chang (1978) (fig. 1) has stimulated the attempt at a more detailed geoecological approach on a regional scale. It is based on three pictorial diagrams: Model A: The Monsoon-Tropical Mainland (supplement VIE); B: The Humid Tropical Islands (supplement LX) and C:The Monsoon Tropical Islands (to follow in ERDKUNDE 38,1). The aim is to show the multitude of environments and systems in which rice is, or can be, grown. This is in line with Moormann and van Breemen's (1978) attempts at more land orientated instead of crop-orientated terms. They distinguish the water-land position for rice by the terms fluxial, phreatic, and pluvial. By bunding and levelling of the fields, the retention of water has significant influence on soil and crop. Working of the fields under water (puddling)creates anthraquic rice-ecotopes, including chemical, biological and physical changes of the upper soil layers and the micro-relief. The various rice habitats, distinguished by water-supply, water depth and landscape position, are shown in a toposequence (fig. 2). The ambivalent term rainfed rice should be more precisely differentiated into rice on impounded rainfall and rice-cultivation by direct natural flooding; likewise upland-rice into shifting cultivation (swiddening, seed by dibble) and dry(land-)rice within permanent arable rotations. The climatic diagrams of humid and dry months are constructed after Lauer and Frankenberg (1981): Precipitation >potential landscape evapotranspiration. Model A comprises discharge-diagrams too, as this paper discusses the rice-cultivation by natural flooding (indicated in darker green) and the melioration of delta and coastal rice-bowls within the monsoonal (A) and the humid (B) tropics. Both, models A and B share the similarities of the wet rice under natural inundation. However, important differences occur with regard to geoecology (as for example where the soils of A fall dry again, whereas those of B remain permanent swamp-soils). This requires quite different cultivation-techniques and adaptations of the rice-plants. Rice-ecosystems with irrigation and with pluvial water-supply will be discussed in ERDKUNDE 38, 1,1984.