1. Introduction
For the past few decades, the population in Lower Casamance has been marked by a strong increase [1]. This demographic growth has resulted in strong pressure on natural resources. This results in soil degradation accentuated by climatic hazards with a corollary of a drastic decrease in agricultural yields. Indeed, in Senegal, the 2011-2012 agricultural season was marked by a sharp decline in groundnut production (59% compared to the previous year and 24% compared to the average of the last five years), following a poor distribution and early cessation of rainfall [2]. In Basse Casamance, the areas planted to groundnuts are the largest with a dominance in the department of Bignona with 24,829 ha for a production of 30,213 tons on 26,691 hectares [1]. In addition, given the problems of environmental pollution due to the chemical intensification of agriculture, farmers are tending to move towards more environmentally friendly agricultural practices. Thus, in the agrarian systems of Lower Casamance, in order to preserve soil fertility and improve their income, farmers tend to conserve woody species of agronomic or socioeconomic interest in their plots. Among these species is Pterocarpuserinaceus. In the fields, Pterocarpuserinaceus is grown in association with crops, particularly groundnuts (Arachishypogea L.), which are very important in the area’s farms. This traditional land use system that associates trees and crops in a random spatial arrangement is called agroforestry park [3]. The species Pterocarpuserinaceus is highly prized by the populations for its many uses including the production of energy wood and timber [4], the production of fodder for livestock [5], pharmacopoeia and medicine [6]. However, despite its socioeconomic importance in farming in Lower Casamance, its influence on groundnut (Arachishypogea) in agroforestry parks remains little studied. It is in this context that this study has set itself the general objective of contributing to a better understanding of the interactions between Pterocarpuserinaceus and the groundnut crop in the agroforestry parks of the department of Bignona.
2. Materials and Methods
2.1. Presentation of the Study Area
The study was conducted in the districts of Tenghory and Kataba 1. The latter belong to the department of Bignona and the region of Ziguinchor (Figure 1). The Tenghory district is located in the east of the department of Bignona and is bordered to the north by the district of Sindian, to the south by the commune of Niaguis, to the west by the district of Tendouck, and to the east by the village of Djibabouya (Sédhiou region).
Belonging to the Lower Casamance, these districts have a climate marked by the existence of two seasons: a dry season and a rainy season and are characterized by rainfall that is everywhere above 1000 mm [7]. The average annual rainfall over the 1980-2018 series is 1302.04 mm [8] (Figure 2). The average monthly minimum and maximum temperature values are 21.5˚C and 35˚C, respectively, during the period 1990-2016 [8].
![]()
Figure 1. Location map of the study area.
![]()
Figure 2. Interannual variation of rainfall from 1980 to 2018 in the lower Casamance recorded at the Ziguinchor regional meteorological station. Source: [8].
2.2. Methods Used
2.2.1. Choice of Communes, Plots and Pterocarpuserinaceus Plants for the Experimental Design
For the collection of data on the influence of Pterocarpuserinaceus on agromorphological parameters of peanuts, three Pterocarpuserinaceus plants were identified and selected in each of the two districts. In order to take into account the heterogeneity of the environment, three different communes were selected in each district for the experimental set-up. Thus, in the Kataba 1 district, one Pterocarpuserinaceus plant was selected in the communes of Djinaky, Kataba 1 and Kafountine, respectively. In the district of Tenghory, one individual of Pterocarpuserinaceus was identified and retained in each of the following three communes: Ouonck, Tenghory and Coubalang. In total, a sample of six (6) Pterocarpuserinaceus plants was selected in the agroforestry parks of the two districts.
In each commune, the choice of the plot for the installation of the experimental device is based on the presence of the groundnut crop variety “Bourkouss” and the species Pterocarpuserinaceus. The P. erinaceus trees chosen are isolated ones, thus allowing the plots to be placed at distances R/2; 1.5R and 2R according to the four geographical orientations (East, West, North and South) without interactions with the crowns of other trees in the park (R = radius of the crown).
2.2.2. The Experimental Set-Up
The set-up was based on three factors: site (boroughs), geographical orientation and distance from the trunk. For each Pterocarpuserinaceus plant selected and following each of the four cardinal directions, three situations were defined: at R/2, at 1.5 R and at 2 R from the trunk (Figure 3). For each situation, a 1 m2 (1 m × 1 m) yield square was set up to evaluate the agromorphological parameters of the peanut. Thus, around each selected Pterocarpuserinaceus plant, 12 yield squares were installed for a total of 72 yield squares (2 districts × 3 feet × 12 yield squares) installed over the two districts.
2.2.3. Measurement of Parameters
The measurement of these parameters was carried out at the time of harvest after the maturity of the peanut.
· Plant height
In each yield square, four peanut plants were randomly selected and their height measured with a ruler.
· Number of pods produced per peanut plant
As with plant height, four peanut plants were randomly selected from each yield square. The number of pods for each stand was counted.
· Pod and haulm yields
After harvesting the peanuts from the yield squares, the pods were separated from the haulm. The harvested pods and haulm from each yield square were weighed on site for fresh weight determination. Then, a composite sample of pods obtained from the four plots in each level for each stand per district was
![]()
Figure 3. Experimental setup around a Pterocarpuserinaceus plant.
taken. A total of 18 samples of haulm and 18 samples of pods for the two (2) districts. These samples were weighed on site to determine their fresh weight using an electronic scale, then placed in an oven at a temperature of 70˚C in the laboratory of the Agroforestry Department of the Assane SECK University of Ziguinchor and weighed every 24 hours until a constant weight was obtained. This was done in order to determine the dry weight of the main production (pods) and secondary production (fane). The results obtained made it possible to evaluate the yield in dry weight of pods and fane per hectare by extrapolation according to the different levels of influence of Pterocarpuserinaceus.
2.2.4. Data Processing
Statistical processing of the data was carried out using XLSTAT software version 2014 which allowed for analyses of variance (ANOVA) with three factors namely site (rounding), geographical orientation and distance from the trunk. Newman and Keuls comparison of means tests were performed at the 5% significance level.
Pod yields per ha were calculated using the following formula:
R (G) = ((PFm.G_P * PS Ech.G)/PF Ech.G) * 10,000
where R (G) = pod yield; PFm.G_P = average fresh weight of pods per plot; PS Ech. G = dry weight sample of pods; PF Ech.G = fresh weight sample of pods. The same formula was used to calculate the pod yield (R (F)) using the fresh weight (PF Ech.F) and dry weight (PS Ech. F) of the pod samples and the average fresh weight of the pod per plot (PFm.F_P).
3. Results
3.1. Height of Groundnut Plants
3.1.1. Effect of Geographical Orientation
The average height of the peanut plants was statistically higher in the North (52.03 ± 15.11 cm) and West (49.88 ± 15.39 cm) orientations compared to the South (45.14 ± 12.09 cm) and East (44.75 ± 14.94 cm) orientations. Thus, a highly significant (p = 0.004) geographical orientation effect in relation to the Pterocarpuserinaceus plant appeared on the height of the peanut plants (Table 1).
3.1.2. Effect of Distance from the Trunk
The effect of distance to the trunk of Pterocarpuserinaceus did not induce any significant effect (p = 0.25) on the average height of groundnut plants in the pens. However, in absolute terms, distance 2R recorded the highest mean height (49.9 ± 14.25 cm) and distance R/2 the lowest height with 46.6 ± 13.36 cm (Table 2).
![]()
Table 1. Variation in the average height of peanut plants in the parks according to geographical orientation.
NS = not significant; *** = very highly significant; ** = highly significant; * = significant.
![]()
Table 2. Influence of distance from the trunk of Pterocarpuserinaceus on average plant height.
NS = not significant; *** = very highly significant; ** = highly significant; * = significant.
3.2. Number of Pods Produced per Groundnut Plant
3.2.1. Effect of Geographical Orientation
The statistical analysis did not show any significant difference (p = 0.6) in the average number of pods produced per plant between the different geographical orientations in relation to the species Pterocarpuserinaceus. However, the North orientation gave the highest result in absolute value (17.19 ± 7.86 pods/plant) and the East orientation the lowest value with 15.58 ± 7.5 pods/plant (Table 3).
3.2.2. Effect of Distance from the Trunk
The results of the statistical analysis revealed a highly significant (p = 0.009) effect of distance from the trunk of the Pterocarpuserinaceus species on the number of pods produced per peanut plant. Indeed, the number of pods produced per plant was higher at distance 2R (18.16 ± 8.33 pods/plant) and lower at distance R/2 with 15.15 ± 6.79 pods/plant (Table 4).
![]()
Table 3. Average number of pods produced per peanut plant in the parks according to geographical orientation.
NS = not significant; *** = very highly significant; ** = highly significant; * = significant.
![]()
Table 4. Average number of pods produced per peanut plant according to distance from the trunk of Pterocarpuserinaceus.
NS = not significant; *** = very highly significant; ** = highly significant; * = significant.
3.3. Effect of Distance from the Trunk of P. erinaceus on Hauln Yield
Distance from the Pterocarpuserinaceus trunk had no significant effect (p = 0.6) on peanut tree nut yield. However, in absolute terms, this yield was greater at distance 2R (2.02 tons DM/ha) and lower at distance 1.5R with 1.56 tons DM/ha (Figure 4).
Statistical analysis did not reveal any significant difference in groundnut treenut yields by district, with probabilities of 0.61 and 0.65 respectively in Tenghory and Kataba 1. However, in absolute terms, regardless of the district, the highest yields were recorded at distance 2R, with 2.52 and 1.51 tons/ha respectively in Kataba 1 and Tenghory. Regardless of the distance from the trunk, the highest treeness yields were recorded in Kataba 1 district (Figure 5).
![]()
Figure 4. Variation in average haulm yield with distance from Pterocarpus erinaceus trunk.
![]()
Figure 5. Variation in average haulm yield according districts and distance from P. erinaceus trunk.
3.4. Effect of Distance from P. erinaceus Trunk on Pod Yield
The results of the statistical analysis showed that the factor distance from the trunk of Pterocarpuserinaceus did not induce any significant effect (p = 0.15) on the pod yield of groundnut. However, in absolute terms, distance 2R gave the best result with 1.45 tons DM/ha and the lowest yield was noted at distance R/2 with 1.03 tons DM/ha (Figure 6).
In both Kataba 1 and Tenghory districts, statistical analysis revealed no significant difference in pod yield as a function of distance from the trunk, with probabilities of 0.65 and 0.61 respectively. As for the pod yield, regardless of the district, the highest absolute yield was recorded at distance 2R with 1.92 tons M.S/ha and 0.97 tons M.S/ha respectively for the districts of Kataba 1 and Tenghory, and regardless of the distance from the trunk, the best results in terms of pod yield were observed in the district of Kataba 1. This yield is significantly higher at distance 2R in Kataba 1 compared to Tenghory (Figure 7).
![]()
Figure 6. Variation in average peanut pod yield according distance from the P. erinaceus trunk.
![]()
Figure 7. Variation in average peanut pod yield according distance from P. erinaceus trunk and districts.
3.5. Prediction of Pod Yield as a Function of Groundnut Haulm Yield
The regression line between pod and treeness yield, with a coefficient of determination (R2) of 0.129 and a correlation coefficient of 0.36, indicates a fairly low correlation between these two parameters (Figure 8). This R2 value indicates that only 36% of the production of groundnut pods is explained by the production of stover. It thus appears that, in addition to vegetative production (haulm production), pod yield is explained by other factors in the parks of Kataba 1 and Tenghory districts.
![]()
Figure 8. Linear regression of peanut pod yield and haulm yield parameters.
4. Discussion
This work is a contribution to a better understanding of the interactions between Pterocarpuserinaceus and peanut cultivation in agroforestry parks in the department of Bignona. The study showed that the geographical orientation of the Pterocarpuserinaceus plant significantly influences the height of the peanut plants. Indeed, the height of the peanut plants is statistically more important in the positions less exposed to solar radiation: North (52.03 cm) and West (49.88 cm) compared to the most exposed positions (South (45.14 cm) and East (44.75 cm)). This is because as the amount of light received by the plant decreases, the plant interprets these signals as cues to the proximity of competitors [9]. Thus, the plant grows rapidly and engages in a race for light, promptly elongating its stems and petioles. Lateral buds are inhibited, which limits horizontal branching: this is apical dominance (conflicting vertical elongation or shade-avoidance syndrome). However, there was no significant difference in the number of pods produced per plant according to geographical orientation. However, in absolute value the North orientation showed the highest result (17.19 pods/plant) and the East orientation the lowest value with 15.58 pods/plant. This is justified by [10] according to whom the absence of light as well as the presence of a certain humidity linked to the pod’s need for calcium, are necessary for its development. Indeed, evapotranspiration is less important on the side less exposed to light. This would explain the greater number of pods per foot on the side less exposed to sunlight. In addition [11] point out that the number of pods per peanut plant decreases as the amount of water supplied for the plants decreases.
The factor distance from the trunk of Pterocarpuserinaceus did not induce any significant effect on the average height of groundnut plants. This same result was found by [12] on Sterculiasetigera indicating that after 3 months, groundnut height growth did not vary significantly with distance from the trunk. In contrast to the result observed for plant height, distance to the trunk of Pterocarpuserinaceus species had a highly significant effect on the number of pods produced per peanut plant. The number of pods produced per plant was higher at distance 2R (18, 16 pods) and lower at distance R/2 with 15, 15 pods/plant. These results corroborate those obtained by [13] who stated that under the tree, the number of pods/plant is lower than the control (outside the tree canopy), but this difference is only significant at the level of the Faidherbiaalbida canopy boundary. Groundnuts require maximum sunlight at flowering, so even light shading would reduce pod production.
The distance factor from the Pterocarpuserinaceus trunk did not induce any significant effect on peanut taffy yield and pod yield. However, in absolute terms, the yield was higher at distance 2R (2.02 tons DM/ha) and lower at distance 1.5R with 1.56 tons DM/ha for the hay. For pods, distance 2R gave the best result in absolute value with 1.45 Tons DM/ha and the lowest yield was noted at distance R/2 with 1.03 Tons DM/ha. These differences in absolute value are in accordance with those of [12] who showed that groundnut pod biomass increases with distance from the trunk of S. setigera. In addition, [5] found that cowpea causes a decrease in groundnut pod yield in Senegal. These results are also in line with [14] who showed a slight loss in production near the trunk and a small non-significant increase at the crown line. And that the reduction in pod production below the crown could then result from the synergy of the two factors. These factors are the increased imbalance between nitrogen, which is in sufficient quantity to promote a significant increase in tassel production, and the reduction in sunlight, which must be maximal at this stage of the plant’s physiological development to obtain good fruiting. In addition, competition for water and nutrients may contribute to this reduction in groundnut yields near the tree [12]. However, the results for haulm yield differ from those of who argue that the tree significantly improves haulm yield within 5 m of the Faidherbiaalbida crown. In absolute terms, both the haulm and pod yields are higher in the Kataba 1 district than in Tenghory. Pod yields were even statistically higher in Kataba 1 than in Tenghory at the 2R distance from the Pterocarpuserinaceus trunk. This could be explained by a difference in soil conditions between the two districts. Indeed, the behavior of the plant stand and the yield of the crops depend on factors related to the natural environment: soil, climate; factors coming from the genetic “material” and factors coming from the farmer [10] [15]. The average yield obtained in this study varies between 1.45 Tons DM/ha and 1.03 Tons M S/ha for pods and between 2.02 Tons DM/ha and 1.56 Tons DM/ha for tops. These values are higher than those obtained by [13] in Senegal who recorded an average yield between 1289 kg DM/ha and 1179 kg DM/ha for pods and 990 kg DM/ha and 1492 kg DM/ha for haulm. These yields are also higher than those obtained on the African continent for pods, estimated on average at 1 t/ha [16]. According to [17], this difference in production is due to the fact that the yield of a groundnut variety in a given environment depends on the individual possibilities of the plants and the population density. Individual production is a function of the number of mature fruits and the average weight of each fruit.
5. Conclusions
The study aimed to evaluate the effects of Pterocarpuserinaceus on the agromorphological parameters of groundnut in the parks of the districts of Kataba 1 and Tenghory. It showed that the geographical orientation of the Pterocarpuserinaceus plant significantly influences the height of the groundnut plants. Indeed, the height of the peanut plants was greater in the positions least exposed to solar radiation (52.02 ± 15.11 cm in the North and 49.88 ± 15.39 cm in the West) compared to the most exposed positions (South and East). However, there was no significant difference in the number of pods produced per plant according to orientation.
The factor, distance from the trunk of the Pterocarpuserinaceus species, did not induce any significant effect on the average height of the plants, the yields in fane and pods of groundnut. However, it did have a significant effect on the number of pods produced per peanut plant. The number of pods produced per peanut plant was higher at distance 2R (18.16 ± 8.33 pods/plant) and lower at distance R/2 (15.15 ± 6.79 pods/plant).
However, it would be interesting to continue the studies to:
· Measurements of other variables such as soil fertility and water balance as a function of distance from the tree trunk in order to better explain the effect of distance from the trunk on peanut crop behavior;
· Extend this study to other crops grown in the parks of Bignona Department, such as millet.