Cacao Water Use, Canopy Characteristics and Yield as Affected by Irrigation and Shade in a Rainforest Zone of Nigeria

Abstract

There has been need to improve crop and water productivity considering the need for agricultural intensification  in the realm of increasing water scarcity and drought in several regions of the world. Information is limited about the effects of irrigation on cacao water use (evapotranspiration)  especially, during the terminal drought situation of the dry season in the rainforest agroecology of Nigeria. The effects of shade and dry season irrigation was examined on tree water use, canopy characteristics and pod and bean yields of cacao (Theobroma cacao L.). Treatments were 2 by 2 factorial combinations of irrigation intervals (5 and 10 days) and shade and no-shade (open sun) laid out in a split-plot scheme with 3 replications. Shade regimes constituted the main plots and irrigation intervals the sub-plot treatments. Irrigation water was delivered at 5-and 10-day intervals on emitter lines using gravity drip system. Irrigation combinations affected cacao canopy characteristics (leaf area index) and light integrals (photosynthetic active radiation (PAR) and canopy light attenuation (extinction coefficient, k) within the cacao field. The unshaded-irrigation had higher proportion of incident radiation (I) transmitted (Io) through the canopy (IO/I), PAR intensity, and canopy extinction coefficients (k) compared with the shaded plus irrigations at 5-and 10-day intervals. Cumulative seasonal irrigation (12119 and 8483 mm), soil moisture contents (19.6 to 13.7 %) and cacao water use (ETc:  3.8 and 3.2 mm.day-1) differed for the respective 5- and 10-day irrigation intervals. The unshaded plus 5- and 10-day irrigation intervals out-yielded the shaded-irrigation combinations for number and weights of pods and beans.  Pod and bean yields were significantly different under irrigation treatments, the 5-day irrigation produced greater number and heavier pods and beans compared with the 10-day irrigation.  For the shade-irrigation combinations the range of values were: weights of pods (78000 to 6000 kg/plant), beans (4.8 to 3.2 t/ha) and water productivities: Irrigation WUE: 0.45 to 0.33 mm/kg/ha) and ET WUE: 0.11 to 0.09 mm/kg/ha). The shade-irrigation strategy enhanced cacao leaf area index, water use and bean yields and ameliorated climate stress.