In the Plain of Reeds, Vietnam, the characteristics, water levels, and water quality of acid sulphate soils are highly variable in space and time, in relation to micro-elevation, and hence, favourable conditions for crop production are met during a very short period. Yield components were analysed in recently reclaimed farmers' fields. A semi-quantitative model was developed, explaining rice growth and yield as a function of different biophysical conditions on severely acid sulphate soils. Intra-field variability of rice growth and yield was explained by the high short-range variability of soil and water, which was explained by micro-elevation. Long submersion and deep reduction were important agronomic problems in the beginning of the plant cycle and led to low plant, tiller, and panicle densities. Strong oxidation leading to acidification and solubilisation of aluminium. was frequent at the end of the cropping season and was responsible for poor plant growth and grain filling. Inter-field variability of plant growth and yield was explained by differences in soil and water in relation to mean field level and number of years after reclamation. A typology of fields based on rice development is proposed as a guideline to extension in the Plain of Reeds.
