Agromorphological characteristics of Irvingia gabonensis (aubry-lecomte ex o'rorke) baill. (Wild mango) and Theobroma cacao L. in traditional agroforestry systems
Description
Cocoa farming has grown exponentially, reaching over 4 million ha of cultivated land. The predominant expansion of cocoa farming from east to west has led to the degradation of the forest landscape. Today, the restoration of the environment and forest cover is a key issue for all agricultural development programs, including cocoa farming. Thus, the socially sustainable, acceptable and profitable ecological alternative to conventional cocoa farming remains agroforestry. This is a dynamic system of natural resource management based on ecological foundation that integrates trees into farms and thus makes it possible to diversify and maintain production. Agroforestry represents one of the most promising solutions for sustainably linking agricultural production and environmental protection. However, several unclear points remain regarding the choice of woody species and their ecological interaction with the cocoa tree. From a technical point of view, it is important to combine species that have favorable effects on the cocoa tree to ensure satisfactory agricultural production. This species is highly valued by farmers in western and south-western Côte d'Ivoire for food and trade. Its kernels are an important nutritional supplement (vitamins, fats, proteins, minerals), and their marketing provides rural populations with financial income. However, there is still a lack of knowledge about the characteristics of I.gabonensis and its interaction with cocoa. The study was initiated with a view to ensuring sustainable cocoa production. In Côte d'Ivoire, I.gabonensis is frequently grown in association with cocoa. The hypothesis behind this study is that the ecological interaction between I.gabonensis and the cocoa influences the agromorphological characteristics of the cocoa. Our study contributes to improve cocoa production systems for sustainable farming. More specifically, we aimed to describe the structural characteristics (height and diameter) of I.gabonensis, to assess its productivity and to describe its effect on agro-morphological characteristics of cocoa trees. To reach this goal, a design of 10 and 20 m radii was set up around the Irvingia gabonensis species, in which diameter, height, morphological characteristics of fruits and seeds, biomass and carbon stock were assessed. The results revealed a homogeneity of I. gabonensis morphological characters as well as fruit production, biomass and carbon stock in all localities, with the exception of height. The vigour and pod yield of cocoa trees in the vicinity of the species was reduced, given the low cocoa density observed in its surroundings. Its presence in cocoa plantations increases biomass production and carbon stock. I gabonensis stabilizes the rate of rotted and gnawed pods. I. gabonensis could therefore be integrated into agroforestry plots, provided that the cocoa density around it is reduced to minimize its impact on cocoa vigor and yield.
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Irvingia gabonensis Dendrometric measurements, for each tree, the height was measured using a VERTEX dendrometer, and the circumference at breast height (DBH) at 1.30 m from the ground. Individual circumference values were converted to DBH using the following formula: D = C / π, Avec C - Circonference, D - Diameter, et π - 3,14. Above-ground biomass (AGB) was calculated using the allometric model of [8]. AGB=0,0673*(ρD2H) 0,976 (kg), DBH - Diameter at breast height (in cm) AGB - Above-ground biomass (kg), ρ - Specific density of wood (g/cm3), H - Total height of I.gabonensis trees (m), DBHs were measured at 1.3 m from the ground [40] and the wood density of I.gabonensis is 0,71 g.cm-3 The Underground Biomass (UB) of the trees was estimated by multiplying the value of the above-ground biomass (AGB) by a coefficient of value estimated at 0,24. UB = AGB x R (kg) R - Conversion coefficient from above-ground to below-ground biomass The total biomass (TB) of standing woody plants was estimated by adding the above-ground biomass to the underground biomass. Carbon stock was determined by the formula. C (tC/ha) = ρ × TB (kg) Productivity was assessed on the basis of tree fruit load over a 12-month period. The number and weight of fruits collected were determined per tree. Fruit shape, seed and fruit length and width were determined using a graduated scale. To analyse the Influence of Irvingia gabonensis on Theobroma cacao agronomy, the circle method modified and adapted to our study, was used. On each tree, radii of 10 and 20 metres around each I. gabonensis, taking them as the center of the circle, were delimited. Data on the density, vegetative vigor, yield, biomass and carbon sequestration capacity of cocoa trees around I.gabonensis trees were collected in the circles with radii of 10 and 20 m. Cocoa density was assessed by counting the number of cocoa trees in each radius. The vigour of cocoa trees in the vicinity of I. gabonensis was estimated by measuring crown diameter and height, using the method of Lachenaud and Oliver. The calculation method used for Irvingia gabonensis trees was the same as that used for cocoa trees. However, the diameter of the cocoa trees was measured at 20 cm from the ground and the density is 0.43 g.cm-3. The rate of healthy, gnawed and rotten pods on each tree was determined in each radius. The data collected allowed us to estimate cocoa productivity and pod health under the influence of Igabonensis tree.