RESEARCH PAPER EffECt of tAPPing diRECtion in RElAtion to Sun ligHt on gum ARAbiC AcAciA senegAl (l.) Willd. YiEldS in noRtH KoRdofAn StAtE, SudAn

IdrIs Musa adaM1, MohaMed el Mukhtar Ballal2 and kaMal e.M. Fadl3

AbStRACt

this study was carried out at el demokeya Forest reserve over two seasons (2006/2007 and 2007/2008) to determine the effect of tapping direction in relation to sun light on the yield of gum arabic from Acacia senegal. a randomized complete block design experiment with three replications was conducted. the treatments consisted of tapping on the eastern, western, northern and southern sides of the tree. The number of trees per treatment was 10 and 15 in the first and second seasons, respectively. A highly significant difference between tapping direction (P≤ 0.001) was obtained in all pickings except the third picking in the first season and the first picking in the second season. the gum yield increased by 60 % when the tapping was on the eastern and western sides towards direct sun light. The combined analysis showed significant differences (P≤ 0.05 and P≤ 0.001) on total gum yield (g\tree) and the number of trees yielding gum. Therefore, tapping of Acacia senegal tree on the eastern and western sides is recommended.

Key words: semi-arid area, exudates, non timber forest product (NTFP)

intRoduCtion

Gum arabic is defined as the dried exudate obtained from the stems and branches of Acacia senegal (l.) Willd. awouda, (1974) Fao, (1990) and anon, (2004) added some other related species to this definition. Gum arabic is of major economical importance to the country and to the small gum producers in the gum belt of the sudan. the environmental and economical importance of the gum arabic has been documented by many authors (IIed and Ies, 1989, Barbier, 1990; Coppen, 1995; and Ballal, 1991). In areas too dry to support agriculture and livestock production, gum arabic is often the principal source

1Agricultural Research Corporation, Kadugli Research Station, P.O. Box 10, Kadugli, Sudan.2Agricultural Research Corporation, El Obeid Research Station, P.O. Box 429, El-Obied, Sudan.3Agricultural Research Corporation, El-Obied Research Station, P.O. Box 429, El-Obied, Sudan e-mail address:kamaleldin2001@yahoo.com. Paper received 18.12.08; accepted for publication ****

Forests, Trees and Livelihoods, 2009, Vol. 19, pp. 00–00© 2009 A B Academic Publishers—Printed in Great Britain

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of revenue for semi-nomadic people (nas, 1979). Acacia senegal has a high potential in agroforestry systems because it is a leguminous tree that fixede atmospheric nitrogen, improving soil fertility and increasing crop yields (Ballal, 2000). the importance of the tree as an integral component in traditional dry-land agroforestry is also reported by raddad (2006) and adam (2006).

the traditional A. senegal agroforestry system recently has been disrupted through the misuse of land, drought and desertification, and an overall declining trend in gum arabic yield, production and supplies (awouda, 2000; Ballal, 2008). the effects of these factors on gum arabic production have been reported by awouda (2000), oleghe` and akinnifesi (1992), seif el din (1995), and abdel rahman (2001). Ballal (1991) stated that “gum yield varies greatly with differences in husbandry practices namely the time and intensity of tapping, and tapping methods. the objective of this paper was to determine whether the gum arabic yield is affected by the method of tapping – specifically the site of the tapping in relation to the direction of sun light, and to recommend management guidelines to improve gum arabic production.

mAtERiAlS And mEtHodS

this study was conducted at el demokeya forest reserve, (13° 16' n: 30° 29' e: alt. 560 m), 31 km east of el obied town, in Western sudan, also known as Qoz ashgar. the forest was established in 1959/60 in an area of about 3,150 hectares. It is the ever-biggest reserved forest of pure A. senegal “hashab” stands in the sudan, (adam, 2005; Ballal, 2008). the forest also constitutes the only gene bank of high yielding mother trees in Western sudan.

Most of the gum arabic research in the sudan has been done in this forest and it still is the most suitable and well protected site for gum arabic research in the sudan. there are both natural stands and plantation in the forest (adam, 2005). the soil in the sand dune areas is known locally as “Qoz”. these soils

taBle 1

effect of tapping direction on gum arabic yield (g/picking) in north kordofan state (season 2006/2007).

tapping Gum arabic yield (g/picking) total yield direction g/picking 1st pickings 2nd pickings 3rd pickings

east 61.68a 63.61a 49.40a 174.69aWest 51.75a 65.46a 48.61a 165.82asouth 31.22B 27.74B 41.83a 100.79Bnorth 29.43B 22.58B 40.00a 92.01BMean yield 43.52 44.85 44.96 133.32

Means followed by different letters within different tapping direction are significant different (P < 0.05) according to Duncan’s Multiple Range Test.

EFFECT OF TAPPING DIRECTION IN RELATION TO SUN LIGHT 3

taBle 2

effect of tapping direction on gum arabic yield (g/picking) in north kordofan state (season 2007/2008).

tapping Gum arabic yield ( g/picking) total yield g/picking 1st picking 2nd picking 3rd picking 4th picking 5th picking east 49.13a 89.20a 87.99a 80.21a 72.82a 379.35aWest 46.34a 66.22aB 74.61a 56.20aB 45.68B 289.05aBsouth 25.84a 32.91B 35.45B 34.31B 1.50C 130.01Bnorth 22.20a 27.40B 18.07B 25.44B 0.77C 93.88BMean yield 35.88 53.93 54.03 49.04 30.19 193.82

Means followed by different letters within different tapping direction are significant different (P < 0.05) according to Duncan’s Multiple Range Test.

are inherently poor, but their high permeability and the easy penetration of the A. senegal roots, compensate for their low fertility.

the site is a variety of A. senegal savannah, characterized by a low annual rainfall about 300 mm, and monthly minimum and maximum temperatures of about 20°C and 35°C, respectively, the average duration of bright sunshine over the site ranges from 8.9 to 9.8 hours every day, and up 10 hours or more in summer. two experiments with a randomized complete block design and three replications were conducted over the two seasons 2006/07 and 2007/08 in an even-aged stand. In 2006–7 each block was divided into four plots containing 10 trees, but block size was increased to 15 trees in the second experiment. the trees in each plot were demarcated and tapped during november. the treatments comprised tapping the trees in one of the four directions (north, south, east and West). the gum yield was collected six weeks after tapping and further pickings were made every 15 days; the number of trees yielding gum was recorded. nCss software computer program was used for analyzing the data.

RESultS And diSCuSSion

There was a highly significant differences (p ≤ 0.001) in all gum pickings between the different directions of tapping in the two seasons (tables 1 and 2). the mean gum yields per picking from the east and West sides were higher than those from the north and West sides in both the seasons. the average yields from the East and West sides in the first and second seasons were 64.7 and 66.8 g/pick compared to 38.6 and 22.4 g/pick for the north and south directions, respectively. the combined analysis of the two experiments showed significant effects (P ≤ 0.05 and P ≤ 0.01) of tapping on the East and West sides compared to the north and south sides (table 3). Gaaffar (2006) found that light intensity intercepted by the A. senegal leaves range from 500 to 2500 µmol m–2 s–1 and the air temperature ranged from 26 to 41°C. the increase in light

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taBle 3

effect of tapping direction on gum arabic yield (g/picking) in north kordofan state – combined analysis over seasons.

Gum pickings tapping direction s.e ±

north south east West Mean yield (g/picking)

1st picking 24.82B 28.53B 55.36A 49.05A 39.69 4.77* 2nd picking 24.99B 30.33B 76.41A 65.84A 49.39 8.73*3rd picking 29.04B 38.59B 62.01A 68.3A 49.48 6.76*4th picking 34.34C 25.44C 80.21A 56.20B 49.04 11.35*5th picking 1.5C 0.77C 72.82A 45.68B 30.19 12.74*over all mean 20.01 21.53 58.89 48.59 37.29

Means followed by different letters within different tapping direction are significant different (P < 0.05) according to Duncan’s Multiple Range Test.

Figure 1. Gum nodules on east tapping direction

EFFECT OF TAPPING DIRECTION IN RELATION TO SUN LIGHT 5

intensity raises both leaf and air temperatures, reducing the relative humidity of the surrounding air. Ballal (2008) also reported on the effects of humidity and cold on gum yield. temperature and relative humidity were found to explain 67% of the variation in stomatal conductance, (loreto and sharkey, 1990; Mott and Pakhrurst, 1991 and Tailott et al., 2003 as cited by Gaafar, 2006). since the A. senegal is deciduous, the seasonal variations in total leaf cover will affect the amount of direct or diffused sun light received by the canopy.

The highly significant differences in gum yield between the different directions of tapping as presented in the previous tables could be attributed to the increase in light and temperature on the eastern sides of the tree compared to the northern, Western and southern directions. Burning the grass cover under the A. senegal tree is found to increase the gum formation and yield (adam, 2005). however, the negative side effect of burning is that fire may cause death of the young trees. Increasing temperature through direct exposure to the sun, or increasing the heat stress of the tree during tapping or picking by burring off the grass under the tree, decreases the moisture in the plant leaves, stems or branches. awouda (1973) regarded gum formation as a result of adverse environmental conditions such as poor soils, low rainfall and high temperatures. additionally, high temperature is important in drying the surface of the nodules quickly to encourage the formation of rounded, high grade nodules of gum (Figure 1 and 2). the effect of temperature during tapping and gum collection on gum yield was thoroughly discussed by Ballal (2008).

Figure 2. Gum nodules on north tapping direction

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ConCluSionS

the A. senegal gum yield was greatly increased by tapping on the eastern and western sides of the tree. similarly, the number of yielded trees in the east and West directions of tapping was higher than that of the northern and Southern directions of tapping. These findings can be used to improve gum arabic yield.

RECommEndAtion

to increase the gum arabic yield, A. senegal trees should be tapped on the eastern and Western sides of the branches in order to expose tapping to direct sun light.

REfEREnCES

abdel rahman, h.M. 2001: effect of some growth parameters and age on gum and seed yield of Acacia senegal plantations and natural stands in north kordofan. M.sc., Faculty of Forestry, university of khartoum.

adam, I.M. 2005: an ecological study on Acacia senegal (l.) Willd. With emphasis on understory cover and gum arabic yield. M.sc. thesis, university of kordofan, sudan

adam, I.M., 2006: effect of understory cover and date of tapping on gum arabic yield of A. senegal in a forest reserve in north kordofaan, sudan. Conference on International agricultural research for development, tropentag, university of Bonn, Germany.

anon, 2004: non-wood forest products for rural income and sustainable forestry – edudate GuMs 2, Gum arabic, Gum talha and other acacia Gums. http:// www.fao.org/docrep/v926e/v2336e05.htm, date accessed, (7/8/2008)

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