ACCUMULATION AND PARTITIONING OF DRY-MATTER IN WATER YAM

There is a scarcity of held-growth data from which a yam (Dioscorea alata L.) grow th model could be developed to promote agrotechnology transfer of the crop in the tropics. A 2-yr field study w as conducted on Corozal soil (clayey miued isohyperthermic Aquic Tropudults) in an initial effort to collect data on patterns of leaf area development and dry matter accumulation and partitioning among various plant parts during growth and development of yam plants. In the first year of the study, plants of D. alata cv, Gunung were subjected to fertilizer rates of 0, 667, 1333, 2000, and 2667 kg ha(-1) of a 15-2.2-12.4-3% (N-P-K-Mg) commercial mixture at 50 d after planting (DAP). Biomass harvests were conducted at 60, 90, 120, 150, 180, and 210 DAP. For all plant parts studied, dry matter content was not significantly affected by fertilizer treatment. Even after excluding application of fertilizer during the second year, there were no statistical differences in total and tuber dry matter content between years. Maximum leaf area index values (LAI approximate to 8) Here attained by 140 DAP. During this period, leaves and vines accounted for at least 80% of the total plant dry matter; thereafter, their dry matter content declined. After 140 DAP, increases in total dry matter were the result of rapid increases in tuber dry matter accumulation, The lack of response to fertilizer treatment and high tuber dry matter production suggest that the preplanting soil nutrient status was adequate to support optimum growth of the yam cultivar used during both years of this study, even without the application of fertilizer.