To identify the factors influencing rice (
Oryza sativa
L., cv "Yunnan 3") yield, 37 highland (1,300-1,700 m asl) marsh soils previously cultivated with or without water control, were sampled. Physical soil characteristics were related to organic carbon (C) content which ranged between 8.5 and 360 g C kg
-1. When soils were flooded, the redox potential (pE) decreased from 9.5 to 3.5, pH increased (from 4.6 to 6) and Fe
2+ dominated the exchangeable cations (48% of the ECEC). Exchangeable Fe
2+ and iron saturation ration Fe
2+/ECEC increased with pH and C content. The shift between exchangeable cations was better seen when concentration per unit volume rather than mass was used. Yields were greater (up to 6000 ka ha
-1) in waterlogged eutrophic mineral soils belonging to the USDA Soil Great Groups: Tropaquent, Tropaquept, Hydraquent, Acid peat soils, (Tropohemist, Troposaprist) were less suitable, and were supposed to induce iron toxicity. Potential yields were computed from climatic data and observed data recorded during the rice cycle. Mean grain yield (2,800 kg ha-
1) was 27% of the potential yield. Irrespective of diseases, the marshes seemed to have the same climatic yield potential. Though yield losses due to diseases averaged 16% of the potential yield, soil water control and nutrient availability were the main limiting factors of rice yield under farmers practice in the marshes of Burundi.
