Assessment of Soil Fertility Status for Bambara Groundnut Production in South-eastern Tanzania

Intensive farming practised in the agro-ecological zones of Makonde plateau (C2) and Inland plain (E5) of south-eastern Tanzania without proper soil management has led to nutrient depletion. The objective of the study was to assess the fertility status of soils in Bambara groundnut growing areas of south-eastern Tanzania. Twenty-two farmers' field sites were sampled and composite samples of top soil at 0 – 20 cm depth were collected for physical and chemical analysis. The results indicate that the soils in the study area are sandy loam (64%), loamy sand (27%) and sandy clay loam (9%). About 28% of the soils in the study area had very low CEC values (< 6 cmol (+) kg soil). Soil pH was strongly acidic to moderately acidic (≤ 5.5) and slightly acidic (≥ 6.0) in the C2 and E5 agro-ecological zones, respectively. Total N was very low (< 0.1%) and organic carbon was very low to low (< 0.6%). Low levels of available P (<10 mg/kg), inadequate S (SO4-S) levels (< 10 mg/kg) were observed. The exchangeable K in the C2 zone was very low to low (< 0.05 cmol(+)/kg) while E5 zone had medium K level. The calcium level of C2 was low to medium (0.2 – 2.5 cmol(+)/kg) whereas that of E5 was medium to high (0.6 – 5.0 cmol(+)/kg). The exchangeable Mg2+ levels were very low to low (< 0.2 cmol(+)/kg) while Na+ was < 0.30 cmol(+)/kg soil indicating no sodicity problem. For > 90% of the studied soils extractable Zn was below critical level of 0.6 mg/kg. All soils had adequate extractable Fe whereas > 70% of the soils had high (> 5 mg/kg) extractable Mn. The study area generally indicated low fertility status in terms of N, P, K, S, Mg and Zn, calling for proper management for improving crop production.