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Causes for Anomalous Wet-dry Season Yield Differences in Lowland Rice¹

Field research in the Llanos Orientates (Eastern Plains) of Colombia confirmed the existence of an abnormal yield pattern in lowland rice (Oryxa saliva L.). With uniform irrigation and cultural practices throughout the year, grain yields were consistently lower during the dry than during the wet season. The constant tropical climate was of minor influence; shorter daylength during the dry season was the only factor that had a small negative effect on yield. High fertilizer applications did not raise dry season yields to wet season levels, hence major elements were not considered deficient. Low yielding dry season crops suffered major stress at early stages of growth. Depression of leaf area development and growth were possibly greater during the dry season due to toxic Fe levels in the plants. This resulted in small sink sizes and low yields. Iron toxicity was probably more serious during the dry than during the wet season due to differences in physico-chemical status of soil at planting.

Key Words: Seasonal yield pattern • Solar radiation • Photoperiod • Early vigor • Sink size • Fe toxicity • Oryza sativa L.

² Postdoctoral fellow, CIMMYT Durum Wheat Program, Apartado Postal 6-641, Mexico 6, D.F., and coordinator, CIAT Cassava Program, Apartado Aereo 67 13, Cali, Colombia, respectively.