Uptake of micronutrients by Acacia senegal varieties and its effect on gum arabic quality

Abstract

A study was conducted to establish the uptake of micronutrients by two Acacia senegal varieties established under arid and semi-arid conditions, and its subsequent effect on the quality of gum arabic exudates. Soil and gum arabic samples from the experimental sites at Solit, Kapkun, Kimorok and Maoi in Marigat division, Baringo district, were collected, dried and analysed to establish their baseline physical and chemical characteristics. Glasshouse pot experiments were conducted using the same soil and vermiculite media to determine uptake of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) by Acacia senegal seedlings. A randomized, split-plot design that simulated the environmental conditions in the field was used in treatments varying from normal, low and high concentrations of the micronutrients applied. The soil types varied significantly (P < 0.05) in the level of calcium (17.3, 5.7, 6.4 and 5.0 cmol. ()/kg) and magnesium (6.1, 3.3, 4.0 and 2.7 cmol. ()/kg), respectively, at the study sites. The average copper uptake (103 ppm) by Acacia senegal variety senegal in Solit on dry matter (DM) basis was significantly higher (P < 0.05) than that at Maoi (41 ppm), Kimorok (33 ppm) and Kapkun (30 ppm). Gum arabic from Acacia senegal variety senegal in Kapkun and Solit had concentrations of 45 and 40 ppm Cu, which reveal that Acacia senegal variety senegal tends to take higher Cu levels (108 and 156 ppm) from the soils than that of Acacia senegal variety kerensis at Kimorok and Maoi (38 and 32 ppm). Iron and manganese uptake by the variety (654 and 638 ppm) at Kapkun was significantly higher (P < 0.05) than that of the variety at Kimorok (366 ppm Fe and 307 Mn), respectively. Zinc uptake by Acacia senegal variety kerensis at Kimorok(533 ppm) was significantly higher (P < 0.05) than in Maoi (233 ppm), Kapkun (224 ppm) and Solit (141 ppm). The gum arabic had ash content of 2.88%. Analysis showed that the ash content had a concentration of Zn (124 ppm) which indicated that Acacia senegal variety kerensis tend to take higher concentrations of Zn (533 ppm) from the soils than that of Acacia senegal variety senegal (141ppm). Moisture, ash and volatile matter contents in gum arabic from Acacia senegal variety senegal were 14.9%, 3.16% and 64.24%, while Acacia senegal variety kerensis had 15.2%, 2.88% and 63.8%, respectively. Gum arabic obtained from Acacia senegal variety senegal had higher levels of copper (45 ppm), iron (1415 ppm) and manganese (109 ppm) compared to variety kerensis which by contrast had higher levels of zinc (124 ppm) and nitrogen (0.34 %), respectively. All these levels however fell within the ranges quoted in the International Standard Specifications (0.26% - 0.39% N, iron (730 - 2490 ppm), manganese (69 - 117 ppm), zinc (45 - 111 ppm), ash 2 - 4% and moisture 13 - 15%, respectively). The quality parameters of gum arabic may partly depend on soil characteristics, climate, and availability of the nutrients in the soils.