Contents of micronutrients in different vegetables grown in different locations in Tanzania: implications for soil fertility and nutrition potential of the vegetables

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Sokoine University of Agriculture, Tanzania.


Samples of twenty two different vegetables were collected from different locations in Tanzania, in three replicates, with the objective of determining their micronutrient contents. The samples were washed, dried, ground, and asked in a muffle fiunace. The ash was dissolved in 10% nitric acid and the extracts made to volume in 25-m1 vohunetric flasks. Copper (Cu), zinc (Zn), manganese (Mn) and iron (Fe) were determined using atomic absorption spec trophotorrktry. The data were subjected to analysis of variance. Results showed that the different types of vegetables contained different quantities of the nutrients. For example, Cu ranged from3.75 ng/kg in egg plant to 8.26 Ingice in sweet potato leaves. Zinc ranged from 13.54 mg/kg in African egg plant to 49.89 mg/kg in cassava leaves (rubber type). Manganese ranged from 15.21 rug/kg in egg plant to 137.19 mg/kg in cassava leaves (cassava) and Fe ranged from 102.08 in African egg plant to 478.11 mg/kg in Chinese cabbage. Within a given type of vegetable, nutrient contents were different across locations of sampling. For example, Cu in amaranthus fiomMorogoro varied from 6.25 rraikg to 7.5 rag/kg, while that fiomMbeya varied from 5 ng/kg to 10.62 mg/kg. Zinc in amaranthus from Mbeya varied from 25.31 rrg/kg to 40 n-alg, while from Vumari- Sank Zn varied from30.31 ap-ika to 39.06 nalg. Manganese in amaranthus fiom Mbeya varied from 89.37 rig/kg to 110 ng/kg, while from Morogoro varied fiom31.25 ng/kg to 35.62 ng/kg. Iron in amaranthus from Vumari-Sane varied from 318.75 mg/kg to 409.37 nig/kg, while from Morogoro Fe varied from 425 mg/kg to 531.25 nvkg. Similar variations were observed in the other types of vegetables. Copper was rated as being low (for pregnant and lactating women). Zinc was generally rated as being low; the rest of the nutrients in the vegetables were deeded adequate for human nutrition.


Tanzania Journal of Natural & Applied Science


Micronutrient contents, Soil fertility, Tanzania, Vegetable micronutrient composition