Effects of seed rates and plant populations on canopy dynamics and yield in the greater yam ( Dioscorea alata L.)

Abstract

Four seed rates (1, 3, 5, and 7 t ha −1) and four plant populations (20, 45, 70, and 95×10 3 plants ha −1) of the ‘6322’ accession of greater yam were combined in a two factorial experiment. Measurement of LAI showed that canopy growth progressed proportionally with the seed rate. Canopy growth was not significantly influenced by plant population. A better distribution of small plants derived from higher populations most likely compensated for the higher growth rates of less densely distributed plants derived from low populations. Higher LAI caused by higher seed rates (larger setts) resulted in higher leaf area duration (LAD) and light interception (Li) throughout the growth cycle. The seed rate also strongly affected the yield components, whereas the effect of plant population was only significant for the commercial tuber yield and the number of non-commercial tubers. Nevertheless, a clear maximum among the yield components was only found for the number of commercial tubers. A ridge analysis was carried out to identify possible optima for combinations of the other variables. Commercial tuber yield tended to increase asymptotically with increasing sett size. For total yield, however, tuber production was a function of seed rate and did not respond to plant population, except at the lowest seed rate. The product of plant density and number of stems per plant should be the variable used to explain intercepted radiation in yams. Therefore, the effect of secondary spires on yam canopy dynamics rather than the plant population effect alone requires further study.