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Growth and yield responses of selected cowpea (Vigna unguiculata L. Walp) cultivars to weather and soil factors of the sowing seasons

S.O.Agele, O.M.Agbi

Experiments were conducted at the Teaching and Research Farm of the Federal University of Technology,Akure, a humid rainforest zone of southern Nigeria to examine the effects of the prevailing weather conditions of the rainy and late sowing seasons on growth and yield of three cultivars of cowpea (Vigna unguiculata L. Walp). The cultivars (Ife brown, IT93K-U52-1 and IT89KD-341) were chosen on the basis of contrasting maturity and seed yield, and were sown during the rainy and late seasons of 2008 and 2009. The sowing seasons were characterized by varying amounts of rainfall, solar radiation, open water evaporation (Eo), humidity (vapour pressure deficits – vpd) and temperatures. Seasonal effects were significant (P>0.05) on cowpea growth and seed yield. However, within a sowing season, the cultivars differed in their responses in terms of growth duration, drymatter production and seed yield. In both seasons, shoot biomass is greater in Ife brown while IT89KD-341 had significantly (P>0.05) higher seed yield than cultivar IT93K-U52-1, Higher shoot dry weights were produced by late maturing cultivars IT93K-U52-1 and Ife brown which also produced lesser weights of seeds. Late season cowpea out-yielded the rainy season crop in terms of total weight of pods and seeds produced per plant. Functional relationships between some weather variables and growth and yield characteristics of cowpea were established. These relationships gave a regression coefficient (R2) which shows that, about 40% of shoot biomass and seed yield can be explained by a combination ofweather parameters such as cumulative rainfall,minimumtemperatures, openwater evaporation, vapour pressure deficit (humidity) and thermal time requirements during the respective rainy (April - July) and late (September – December) seasons of sowing. It is concluded that the soil and weather conditions of cropping seasons are critical factors in the processes of determination of growth and yield of cowpea.