Abstract

This study deals with the response of Dioscorea alata to NPK-Ca fertilization as affected by differences in weather conditions in two growing seasons. Experiments were conducted in the central Côte d’Ivoire in 2006 and 2007. The experimental design was a randomised complete block design with 4 replications. The dose of 160-10-180-110 kg ha^-1 of NPK-Ca, respectively was compared to the control (no fertilizers applied). Growth parameters and weather conditions were measured during the growth periods. Rainfall and solar radiation varied much between the two years. Fertilization has significantly increased the tuber yield of both years. In 2006, however, this increase in aboveground organs dry matter was not reflected in tuber dry matter increase, suggesting possible physiological imbalance in which fertilizer has favoured top growth over the tubers. This resulted in higher leaf area index and lower fresh tuber yield. This physiological imbalance could be related to higher water supply during the vegetative period in 2006. Although the weather conditions varied much between years, the leaf area index and the fresh tuber yield were similar between years under non-fertilization, indicating a good adaptation ofD. alata to low soil fertility across the year. Explanations are needed to understand source (leaves) - sink (tubers) relationship in yam and investigation to clarify implications of mineral fertilizers in this important process is warranted.

Key words: Dry matter partitioning, fertilization, leaf area index, radiation use efficiency, water distribution, year.