| The present study is an attempt to investigate the effect of inter-cropping systems with tree species Acacia senegal and three traditional agricultural crops of Sorghum bicollar, sesame and groundnut. It also includes to assessment of crops yield and forest tree product Gum Arabic and to understand of certain soil properties.The experiment was conducted during two rainy seasons (2009-2010and2010-2011) at Abu Nama forest reserve in Abu Hugar governorate, Sennar state, Sudan. The Randomized Complete Block Design (RCBD) was used in this study to consider the sample plots. It was carried three inter-cropping systems having different spacing such as4×4m,4×8m and sole cropping (without any trees). Each inter-cropping system has three replications, and each replication has four plots of10×20m size.The measurements of crop yield were considered in this study of plant height, root length, leaf number, flowering time, crop and gum yield. Moreover, to understand the productivity of three agricultural crops and tree gum, certain soil physical and chemical properties were measured in two different soil depths.Soil pH was measured in soil-water suspension (1:2.5) using a corning glass electrode. Nitrogen, Potassium and Phosphorus were determined by the wet-oxidation method of Walkey-Black, Flame Photometric, and Bray and Kurtz methods respectively.The results reveal that there were significance differences between the three treatments considering crop yield and growth parameters of these agricultural crops (sorghum, sesame and groundnut). The findings of this study are:(1) There were significant differences found on height growth between tree species of A.senegal and three agri-crops within these three selected treatments. For two seasons, the highest and the lowest height growth of three agri-crops was found in4×4m inter-cropping and in sole cropping system respectively.(2) Root growth of these three agri-crops was also varied significantly between these two study seasons. The inter-cropping system of4X4m tree spacing attends the highest root length for three agricultural crops, followed by inter-cropping at4×8m tree spacing and the sole cropping.(3) The leaf number for all crops was decreasing at the same time of increasing tree spacing. Significant reduction of leaves was observed in sorghum crop with increasing of tree spacing. However, sesame did not show differences in leaf numbers in these two seasons for three treatments. Moreover, for ground nut, there was found significant differences in leaf number in two growing seasons at4x8m inter-cropping and sole cropping systems.(4) The number of days for50%flowering of sorghum was increasing followed by wide spacing. The result showed no significant differences for sesame at the different cropping systems in the two study seasons. However, for ground nut there are significant differences among the three treatments, such as yield of ground nut was decreasing followed by narrow tree spacing.(5) Considering crops yield assessment, the results showed that inter-cropping system has the higher yield than the sole cropping. During the two seasons, Yield of crops was found higher at the inter-cropping spacing of4×8m as compared with the inter-cropping spacing of4×4m and sole cropping.(6) From the land equivalent ratio, it was clear that inter-cropping system in better than sole cropping.(7) Gum yield from A. senegal trees was decreased when inter-cropped with field crops for both two seasons. It was higher in sole cropping compare to inter-cropping. Moreover, inter-crop spacing of4x8m was found better than4x4m spacing for gum yield.(8) In this study, inter-cropping with A. senegal reveals positive advantages with regard to soil physical and chemical characteristics. Soil parameters, such as bulk density, moisture content and organic matter are decreasing when the soil depth is increasing. Between two inter-cropping systems in two different soil depths, the soil bulk density, pH, moisture content and organic matter was found higher in4x4m spacing than4x8m. However, hydraulic conductivity is not varied significantly between cropping patterns and soil depth. In our study, the highest soil bulk density was found in both soil depths for sole cropping. Hydraulic conductivity extracts showed no significant differences among the different crop systems in both soil depths. Soil pH was found lowest in sole cropping practices. Moisture content and organic matter are found higher in soil depth of0-25cm for three cropping systems.Soil macronutrients such as nitrogen (N), phosphorus (P) and potassium (K), and soil organic carbon were found highest in4×4m tree spacing for0-25cm soil depth. Macronutrients and soil organic carbon was found lowest in two soil depths for sole cropping system. For nitrogen, potassium and organic carbon, there were significant differences were found among the three cropping systems in two different soil depths. However, phosphorus content in three cropping systems between two depths was not varied significantly. In our study, both inter-cropping systems nitrogen content was found higher than sole cropping. Potassium content in both soil depths are decreased significantly at the tree spacing increased. The highest K content was found in4×4m inter-cropping system in depth of0-25cm and25-50cm. In the study, results of available soil organic carbon was showed a general trend, in both soil depths, organic carbon in the4×4m tree spacing was greater than the other two cropping systems.(9) Overall, considering the crops yield assessment within these three treatments, inter-cropping system of4×8m tree spacing is the best practice, and after that4×4m tree spacing and at last the sole cropping system. Inter-cropping with ground nut is more economically beneficial than the inter-cropping with sorghum and sesame. Moreover, ground nut is best suitable agricultural crop suitable for inter-cropping system, develop the site conditions, economically feasible and increase the farmer's income.Moreover, tree species of A. Senegal help to raise the soil fertility and high production of gum Arabic which can compensate the farmers to take the risk of only cultivation of agricultural crops.
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