Abstract
Seasonal variation in rainfall and temperature affects growth and yield responses of okra to sowing date. In the humid and sub-humid zones of West Africa there are substantial variations in the rainfall and temperature during crop production that can be expected to influence growth and yield. Experiments in the South-west of Nigeria were conducted in order to determine optimum sowing dates for okra in monoculture or in mixed stands with cassava during the early and late rainy seasons. Starting in late July 1999 in the late-season crops and in May 2000 in the early-season crops, three sowing dates at 2-weekly intervals were tested in each season. Sowing date significantly affected phenology (time to vegetative growth, flowering and fruiting) with okra sown in May during the early season and in late July/August during the late season, taking the shortest time to reach specific phenological growth stages, but the longest time to attain flowering, fruiting and harvesting stages. May/early June sowings in the early-season crops and late July/August sowings in the late-season crops gave the highest vegetative growth and pod yields and growth and yields declined remarkably as sowing was delayed 2-4 weeks (25-58% decrease by late June and September sowings in the early and late-season crops, respectively). The observed differences appear to have been due to the effect of drought and high temperatures, particularly during the reproductive phase, on assimilate partitioning and supply for pod formation. The results of this study demonstrate the importance of regular assimilate supply for fruit formation and of substantial leaf production prior to the onset of terminal drought and supra-optimal temperatures. In all seasons, cropping systems did not display differences in growth and yields of cassava and okra. It is concluded that early and late-season okra should be sown in May and in late July/August, respectively, to allow the vegetable to develop under the relatively cool temperatures and adequate soil moisture conditions that reduce effects of climate change and maximize pod yield.
