A field experiment was conducted under rainfed conditions in western Sudan at El-Obied Research Farm (130 20/ N; 300 15/ E, Alt 750m) and Eldemokeya Forest Reserve (130 16/N; 300 29/E, Alt, 560m) during the growing seasons 2004/2005 and 2005/2006. The main objective was to investigate tree crop relation whithin the gum cultivation cycle. Parameters measured were soil particle distribution, soil nutrient content, soil moisture, plant height, root lenght, number of pod/plant, fresh weight,dry weight, crop yield, gum yield and the biological nitrogen fixation under the gum cultivation cycle.
The experiment consisted of seven treatments: three plots represented the intercropping of groundnut, sesame and roselle with Acacia senegal; three plots represented groundnut, sesame and roselle in the sole cropping system, while one plot represented the Acacia senegal alone. The treatments were arranged in Randomized Complete Block Design (RCBD) replicated four times. Land Equivalent Ratio (LER) was used to evaluate the productivity and the partial budget analysis was carried out to evaluate the profitability of the different cropping systems.
Signficant differences were obtained for sand and silt content in both sites, while clay content was not significantly different in both sites. The clay content increased with increase in soil depth. The higher sand, silt and clay content under the intercropping system could be attributed to the dense vegetation cover made by the trees and shelter the provided. The nitrogen and organic carbon are signficantly higher in intercropping system in Eldemokeya Forest Reserve compared with sole cropping and pure Acacia senegal. Soil OC,N and pH was not signficant in El-Obied site. Yet the level of OC,N,P and pH was higher under intercropping system.
In the present investigation, Nitrogen, phosphurs and organic carbon are 36, 30 and 17% lower than the result obtained in 1999 in the same site. This could be due to intensive cultivation in the same area. Under the present investigation no nodules were detected in the field conditions.
Plant height were signficantly different for groundnut,sesame and rosele in El-Obied Farm Research. In Elddmokeya Forest Reserve significant differences were observed for roselle in the firest season and for groundnut , sesame and roselle in the second season. Root lenght was signficantly different for sesame and roselle in both sites, while groundnuts ystem was not signficantly different. Fresh weight was significantly different in both sites. The higher fresh weight was found under intercropping system. This could be attributed to sheding effect which limits fruit production more than vegetative growth. Dry weights were signficantly different for sesame and roselle in both sites, while groundnut was not signfiocantly different.
In both sites intercropping systems reduced groundnut, sesame and roselle yields by 26.3, 12 and 20.2% respectively. The reduction in yield in intercropping plots could be attributed to high tree density, which resulted in water and light competition between trees and the associated crops.
The yields of groundnuts and sesame in present investigation were 37 and 21% lower that the yield obtained from the same site in 1999. this could be due to intensive cultivation and probably the high tree density. All the treatments gave land equivalent ratio (LER) more thyan one indicating the superiority of growing the field crops in intercropping with Acacia senegal than the sole cropping systems.
The higher LER (1.72) was obtained when roselle was intercropped with Acacia senegal, while the lowest LER was obtained when groundnuts was intercropped with Acacia senegal.
The economical analysis revealed that all the treatments were economically attractive, becouse they gave positive net revenue. Intercropping of sesame with A. Senegal was more profitable followed by sole sesame. The highest net benefit was recorded when sesame was grown with Acacia senegal followed by sole sesame, roselle with A. senegal, sole roselle, groundnut with, A. Senegal, sole groundnut and A. senegal as a sole crop.