A STUDY ON THE GROWTH AND FIELD ESTABLISHMENT OF COCOA (Theobroma cacao L.)SEEDLINGS IN THE DRY SEASON UNDER DIFFERENT SHADE AND IRRIGATION REGIMES

Abstract

The use of shade and irrigation for enhancing the growth, development and survival of field-grown cocoa seedlings in the dry season were investigated at the Experimental Station of the Department of Crop, Soil and Pest Management, Federal University of Technology, Akure. The treatments were a3 by 2 factorial combinations of shade regimes (Unshaded/open sun, Dense and Moderate shades) and irrigation intervals (5-day and 10-dayintervals) arranged in split-plot design. The shade regime constituted the main plot while irrigation intervals were the sub-plot treatments.Vegetative growth parameters (stem girth, number of leaves and branches/plant and plant height) were enhanced in the open sun in the unshaded (open sun) seedlings than the shaded (moderate and dense shade) seedlings. Seedlings that were irrigated at 5-day intervalswere taller and produced higher numbers of leaves and branches compared with those irrigated at 10-day intervals although treatment differences were not significant (P < 0.05). Flowers were more profuse for unshaded (open sun) cocoa compared with the shaded cocoa.Also, 5-day irrigation intervals enhanced flowering compared with 10-day intervals. Interaction effects of irrigation and shade regimes were significant (P < 0.05) on cocoa growth parameters and irrigation enhanced the effects of shade on cacao.The characteristics of solar radiation within cocoa were affected by the shade and irrigation regimes imposed.The values of the transmitted radiation below canopy from the incident radiation above canopy were highest for open sun followed by moderate and dense shade respectively.The shade intensities affected light integrals (incident and transmitted radiation and photosynthetic active radiation: PAR) within cacao canopy and canopy extinction coefficient (k).The effect of shade was more pronounced on the ratio of transmitted to incident radiation (IO/I)which was higher for open sun. However, the dense shade plus 10 days irrigation interval had the lowest accumulated transmitted radiation compared other shade-irrigation combinations. The estimated values of canopy PAR extinction coefficients (k) showed that significant differences existed among the open sun (unshaded) and the moderate and dense shade intensities. The canopy light attenuation (extinction coefficient k) was significantly higher for open sun compared with the shaded cocoa. The temporal trend of intercepted radiation within cacao field as affected by shade regimes was monitored. Intercepted radiation from transmitted light through cacao canopy for each month was highest in April. Across the months of observation (December to May), open sun had the highest value of incident radiation followed by moderate and dense shade respectively. The temporal trends of ratio of transmitted to incident radiation followed closely the pattern observed by time dynamics of intercepted radiation. The relationships between growing degree days (GDD) and total leaf number (TLN) also between GDD and leaf area index (LAI) were examined respectively. The relationships were characterized by high coefficient of determination (R2) for the respective open, dense and moderate shade treatments. The temporal trend of air temperature within the cacao field showed that open sun had highest temperatures followed by moderate and dense shade respectively. There was increase in air temperatures from December to April with the temperature at peak in April. The inverse of the slope of the regression of the relationship between estimated thermal time (0Cdays) and corresponding total leaf number (TLN) denote the leaf appearance rate (phyllochron in 0Cd/leaf).The rate of leaf appearance was faster in open sun compared with the moderate and dense shade intensities.