Thesis (Ph. D.)--Cornell University, Jan., 1977. / Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 205-209).

Thesis--Utrecht, 1978. / "Stellingen" (1 leaf) inserted. Includes bibliographical references (p. 342-345).

In Lombok (Indonesia), annual cropping patterns in irrigated areas are divided into three cropping cycles of four months each. In better irrigation schemes, there are normally two irrigated flooded-rice crops, i.e. wet season and dry season lowland rice crops in sequence, followed by one non-rice crop cycle during the driest months (this is referred to as the twice-rice system). In less developed irrigation schemes, one lowland rice crop is normally grown during the rainy season, followed during the driest months by two cycles of non-rice crops, or a non-rice crop and a fallow (this is referred to as the once-rice system). In rainfed areas, especially in the vertisol soil areas, there are upland rice systems in the highland or hillsides, and “Gora” (dry seeded-flooded) rice systems in the lowland. In this area, rice is grown only once a year during the rainy season of the monsoon. Farmers in Lombok do not normally fertilise the non-rice crops such as soybean and mungbean grown following rice, and application rates of fertiliser to rice have fallen since the economic crisis in 1998. Therefore phosphorus (P) deficiency may be expected, which may explain the very low yields of soybean and mungbean achieved by farmers in Lombok. With low P, arbuscular mycorrhizas (AM) might be expected to play an important role in plant nutrition, but inoculation with arbuscular mycorrhizal fungi (AMF) increased root colonisation and yield of these crops in a recent field experiment in Lombok. There had been no survey of AMF populations in rice-based systems in Lombok prior to the work reported here, and little such work anywhere internationally. Therefore, an extensive survey was conducted in Lombok on the two main soil types with rice-based systems. Another field survey was conducted in the Riverina rice-growing area (Australia), as a comparative study to the Lombok survey. In Lombok, rice systems with longer total annual flooding duration had lower populations compared with upland or Gora rice systems. It was therefore suggested that the lower colonisation level in flooded rice was due to the flooded conditions, as well as soil chemical properties associated with flooded conditions, rather than the rice plant itself. There are options for improving AMF population for better growth of non-rice rotation crops, or even for rice crop in Lombok as fertilisers become less affordable and their use on flooded rice is declining. The easiest option is to inoculate AM fungi in the nursery or to make nursery beds in a paddock previously cropped with AMF-stimulating species, such as soybean, to start infection on rice seedlings, which should be better with a dry nursery. The second option is to modify the technique of growing rice, such as applying the SRI (System of Rice Intensification) principles, in which rice is grown without flooded conditions but intermittent short flooded and upland conditions. This will keep the soil in an aerobic condition much of the time and should facilitate the development of beneficial microbial populations and activities in the soil, such as AMF and nitrogen fixers. The SRI method has been reported to increase rice yield dramatically, even in soil with low fertility levels. / Doctor of Philosophy (PhD)