Status and variability of soil micronutrients with landforms in the plague focus of Western Usambara Mountains, Tanzania


A study was carried out in Western Usambara, Tanzania to assess the status of soil micronutrients across three geomorphic units viz., plain, escarpment and plateau in order to provide essential information for on-going studies on plague epidemiology. Nineteen soil profiles were opened, described and 54 samples collected for laboratory analysis. Standard methods were employed to analyse soil physical and chemical properties. Micronutrients Fe, Mn, Cu and Zn were extracted by DTPA and quantities estimated spectrophotometrically. Spatial distribution of micronutrients along the geomorphic units and within pedons was studied using descriptive statistics, correlation, ANOVA and means separation was done by Tukey’s test at 95 % confidence interval in Minitab 14 software. Relationships between small mammal and flea abundance and micronutrients were established by regression analysis using R-software. Results showed that DTPA extractable Fe, Mn, Cu and Zn were variable. Fe ranged from 2.13 to 399.4 mg/kg soil, with a mean of 65.3 mg Fe/kg soil across the geomorphic units. Mn ranged from 0.59 to 266.28 mg Mn/kg soil while Cu ranged from 0.25 to 8.19 mg/kg soil with a mean of 2.98 mg Cu/kg soil. Results show that Zn ranged from 0.08 to 19.6 mg Zn/kg soil, with a mean of 1.16 mg Zn/kg soil. Generally, micronutrients declined with soil depth. The micronutrient levels were high in the geomorphic units with the trend: plateau > escarpment > plain. Iron was found to significantly P<.01 and P<.05 influence plague hosts and vectors. The study concludes that micronutrients vary with soils and geomorphic units. Iron had positive influence on plague hosts and vectors. Further research on the relationships between micronutrients, and plague hosts and vectors in different plague foci in the country is recommended.



Geomorphic units, critical levels, trace elements, ecological research, iron, manganese