Browsing by Author "Rwegasira,Rozalia Gration"

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Effects of timing and frequency of leaf harvesting on leaf and seed yields of selected lines of cowpea (vigna unguiculata) in Morogoro, Tanzania
(Sokoine University of Agriculture, 2009) Rwegasira,Rozalia Gration
Cowpea [F7gna unguiculata (L.) Walp.J is consumed both as grain and as a vegetable. 1 practice, in East and West Africa the vegetable leaves are harvested from the same cro[. planted for seed production. The timing of leaf removal and subsequent frequency of the harvesting have great effects on the cowpea plant’s ability to recover from defoliation. An experiment was conducted at the horticulture unit of Sokoine University of Agriculture in Morogoro, Tanzania, to establish threshold levels at which timing and frequencies of leaf harvesting can be combined for optimal leaf and seed yields. Four cowpea lines (Vuli, UG-CP-9,1T97K10687 and Ngoji) were used as main plots in a split split plot design experiment where time to start leaf harvesting (20, 30 and 40 days after planting) was sub-plot treatment and harvesting frequencies of as per appearance, once a week, once in two weeks and no harvesting were sub-sub plots. The experiment was planted during the short rains season between September 2007 and January 2008. Data were collected on leaf yield, vegetative growth and seed yield. Harvesting as per appearance gave highest leaf yields but lowest seed yields. Delaying time to start leaf harvesting increased seed yields at the expense of leaf yield. Line Ngoji produced more leaves and had higher leaf yields than the other lines, but its seed production was low. In this study, the threshold level at which combined leaf and seed yields, with high enough proportion of seed yield of about 45% or more, was when time to start leaf harvesting was 30 days from planting with harvesting frequency once a week. When the threshold -2^jwel criterion was to achieve the highest combined leaf and seed yields, the best —nbination was harvesting at 30 DAP with frequency as per appearance except for line Vuli. With a threshold of monetary equivalent the best combination was when time to start leaf harvesting was 30 days from sowing (T30) with harvesting frequency as per appearance. It has been established also, however, that suitable timing to begin leaf harvesting and frequency of leaf harvesting for optimized leaf and seed yields is cultivar-specific.