Influence of Climatic Variables on Whole-plant Water use of Cocoa under Limited Soil Moisture Condition

Abstract

Cocoa (Theobroma cacao L.) is a cash crop that is cultivated in many tropical regions of the world and is highly productive under favourable climatic conditions. Cocao, being originally an under storey tree of rainforests in tropical America, is traditionally cultivated below the canopy of shade trees. This study is carried out to establish the influence of climatic variables on whole-plant water use of cocoa under limited soil moisture conditions. An experimental plot was made in an even – aged 54 years old cocoa plantation which was demarcated while Water use measurement carried out for 20 consecutive days at the center of the cocoa plantation field at the Federal University of Technology, Akure using the temperature difference method (Sap flow meter). The results of evaporation rate and water consumed by crops led to decrease in soil water in the monitored root zone from 0.049 to 0.015 m3 m-3. Solar radiation reached a high value of 1002.37 Wm-2, with day time average of 238.02 Wm-2. Temperature ranges between 16.41 and 34.19ºC with a daily average of about 24.39ºC. Relative humidity varied from 98.60% to less than 32.37% with daily mean of around 74.90%. Vapour pressure varied from 0.01 to 2.87 kpa. The day time wind speeds rarely exceed 5.2 ms-1 while the daily averages were generally around 1.09 ms-1.  The results also show that transpiration, (Ec) is mostly influenced by solar radiation with a correlation coefficient of 0.71 while other variable like temperature, Vapour pressure deficit, and Relative humidity has correlation coefficient of 0.62, 0.50 and 0.58 respectively. The total amount of rainfall during the experiment was 38.9 mm. This shows that solar radiation has greater influence on the transpiration of the cocoa plant than other variables in the study area.