Yield trends of GUM arabic from acacia senegal as related to some environmental and managerial factors

Gum arabic yield per picking and per unit area and trends were studied at Demokeya (13o 16'39o 29' EAlt,560m) experimental site and El Himaira (13o 19'N30o 10'EAlt.570m) in North Kordofan. The effects of year, time and intensity of tapping were examined at plantations as well as for natural stands of Acacia senegal at the respective sites. In addition, a study of the effect of climatic variables, namely rainfall and minimum and maximum temperatures at tapping and gum collection, was carried out at Demokeya plantation. The objective was to establish a better understanding of causes of variability in gum arabic yield and yield trends in relation to tapping and climatic factors as basis for yield control, prediction and stability. The experimental design for the four sets of experiments, one on a plantation and the other on a natural stand in each site, was a 2-factor randomized complete block with at 6 and 8 levels, respectively. The first tapping treatment was started in 1st October. Each consecutive treatment was started 15 days after the previous treatment up to 15th December. The tapping intensity (number of branches) levels were 1, 2...to 8 branches. Each treatment was assigned to 10 trees in each plantation and to 5 trees in each natural stand. The experiment at Demokeya was continued for 8 years (1992-1999). However, for El Himaira plantation and natural stands at both sites, the experiments were continued for 3 years (1997-1999). Rainfall and minimum and maximum temperatures at tapping and gum collection were recorded for Demokeya plantation throughout the course of the experiment. The results showed that the interaction of tapping time and year was highly significant (P0.001) on yield per picking and per unit area of plantation. The trend in yield per picking is similar for both sites. Yield increases (8and 17at Demokeya and El Himaira, respectively) in the second ppick and then decreases steadily. The maximum yield of the second pick was 57,4g and 24,6g/tree for the two sites, respectively. This shows a 50reduction in yield of the producer's managed pantation. Therefore, the trend in yeild per picking could be relied on to predict or estimate yield in relation to management or that of consecutive pickings. In addition, yield of the first fourpickings contributes 85of the total yield. Moreover, gum yield (g) of the first pick was highly correlated (r=0.93) with total yield (g/tree). The simple regression model based on this relationship was highly significant (p = 0.008) with a coefficient of determination (r2) equals 0.86. Therefore, using this model, yield/tree or per unit area could be predicted. Similarly, tapping date gave a high correlation (r = 0.96) with total yield. This parameter was found to explain 92(r2 = 0.92) of the variabillity in yield/tree, and can thus be used to predicting total yield. Natural stands showed similar results with respect to yield per picking and per unit area. However, gum yield of natural stands was less by about 50than that of plantations in the respective sites, and that yield of El Himaira natural stand is 45lesss than that of Demokeya. Therefore, it is implied that yield of a natural stand in one site kcould be estimated by knowing yield of the other site, and could also help in estimating yield of a plantation in the same or other site. Gum yield was found positively correlated with tapping intensity, rainfall and minimum and maximum temperatures at tapping time, and negatively correlated with tapping time and minimum and maximum temperatures at gum collection. However, the time of tapping, tapping intensity, rainfall and the maximum temperature at gum collectiion were found to explain 73(r2 = 0.73) of the total variability in gum yield per unit area. The regression model involving these variables was highly significant (P0.001). The use of this model could help in: 1) Understanding causes of yield variability in gum arabic production. 2). Predicting yield of a coming year based on rainfall of the previous year under a prescribed plan of tapping. 3) Predicting future yield depending on rainfall, temperature forecasts and average tapping date and intensity used by producers. The study showed that by controlling tapping, the averagte yield in producers' plantations and natural stands could be doubled. Further improvement in yield could be achieved through extension and training to upgrade producers' skills in tapping and gum collection. In this respect, given the present land tenure problems, gum yield could only be sustained through vertical improvement and the incorporation or maintenance of different age gradations in plantation and natural stands within a context of farm forestry. This could be of paramount importaance in North Kordofan environment, where agricultural production seems more risky than gum arabic production