Browsing by Author "Tenga, J. J."

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Assessment of soil fertility status for Bambara Groundnut Production in South-eastern Tanzania
(IJPSS, 2018-09-13) Tenga, J. J.; Semoka, J. M. R.; Msanya, B. M.
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 (SO 4 -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) 2+ whereas that of E5 was medium to high (0.6 – 5.0 cmol(+)/kg). The exchangeable Mg 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.
Optimizing p and k for improving biological nitrogen fixation and productivity of bambara groundnut (v igna Subterranea ) in South-Eastern Tanzania
(Sokoine University of Agriculture, 2019) Tenga, J. J.
Bambara groundnut (Vigna subterranea (L) Verde) is a pulse crop cultivated by smallholder farmers in Tanzania, ranked the third most important legume in the SEZ after pigeon pea (Cajanus cajan) and cowpea (Vigna unguiculata). Farmers in south-eastern Tanzania grow Bambara groundnut primarily for food and sell part of the produce to supplement income of their household. However, the productivity of Bambara groundnut is below the potential yield (< 2 t ha -1 ), and is considered a threat to their livelihood. Among the factors causing low yields of Bambara groundnut include insect pests and disease incidences, poor agronomic practices and low soil fertility. Low soil fertility is amplified by continual mining of nutrient elements from the soil and reduction of soil organic matter content, through the removal and burning of crop residues and without applying balanced nutrients. Balanced supply of plant nutrients is important in order to improve and sustain yields of Bambara groundnut in South-Eastern Zone (SEZ). However, the establishment of the technologies of soil fertility management is hindered by inadequate information on soil characterization and classification of soils. These agronomic experiments would lead to establish technology that would be transferred to other areas of similar soil conditions for Bambara groundnut production, particularly in Tanzania. Furthermore, all developed interventions concentrated on improving Bambara groundnut varieties; plant spacing, morphology and diversity of the crop are known. The information on soil nutrient status including phosphorus (P) and potassium (K) for SEZ is not well known, and the required optimum rates are not yet established. Therefore, the intention of this study was to determine the status of soil fertility and optimum rates of N, P and K for Bambara groundnut production in the SEZ. A standard survey was carried out in the Bambara groundnut growing areas of SEZ, to establish representative experimental sites on the basis of agro-ecological settings and soils. The morphology, genesis, physio-chemical properties and classification of soils based on two international soil classification systems, namely USDA Keys to Soil Taxonomy and the World Reference Base (WRB), were assessed. Three pedons were characterized, namely NNL-P1 at Nannala village in Tandahimba district, MKG-P1 at Mikangaula village and NWJ-P1 at Nawaje village in Nanyumbu district. Disturbed and undisturbed soil samples from genetic soil horizons were analyzed for physico-chemical properties. Soil nutrient status for macro-nutrients (N, P, K, Ca, Mg and S) and micro-nutrients (Fe and Zn) were assessed from 22 soil samples from Bambara groundnut growing areas of south-eastern Tanzania. Field experiments were established on two pedons, namely NNL-P1 and NWJ-P1. The experiments were used to establish optimum rates of P and K for N 2 fixation and yields of Bambara groundnut in south-eastern Tanzania. The treatments for the field experiments were varied rates and combinations of P (0, 20, 40, or 60 kg P ha -1 ), K (0, 40 or 80 kg K ha -1 ) and N (0, 20 or 80 kg N ha -1 ), as sub-plots, in a split plot design replicated three times. The main plots were two varieties of Bambara groundnut (local and improved). The characterization results indicated that two pedons NNL-P1 and MKG-P1 were classified to great group level using the USDA Keys to Soil Taxonomy as Dystrustepts and Haplustepts, respectively, and these translated into Cambisols in the WRB for Soil Resources. Pedon NWJ-P1 was classified as Argiustolls and translated into Phaeozems in the WRB. Over 60% of 22 soil samples analyzed for nutrient status, the limiting nutrients for productivity were N, P K, S, Mg and Zn, which were rated as being very low to low, while Ca was rated as medium in >80% of the soils of the studied areas. It was concluded that low nutrient status especially N, P, K, S, Mg and Zn, needs proper management to improve soil fertility for Bambara groundnut production. Application of P increased N 2 fixation and Bambara groundnut yield significantly. Thus, use of P at the rates of 20 – 40 kg P ha -1 is deemed necessary for high yields in the study area.
Pedological characterization and classification of some typical soils in three agro-ecological settings of South-Eastern Tanzania
(IJSER, 2018-02) Tenga, J. J.; Msanya, B. M.; Semoka, J. M.; Semu, E.; Mwongo, S. B.
This study was carried out in South-Eastern Tanzania to establish representative experimental sites on the basis of agro- ecological settings and soils. Three pedons were characterized namely NWJ-P1 in Nawaje village, MKG-P1 in Mikangaula village and NNL-P1 in Nannala village. Soil moisture and temperature regimes in the study areas were, respectively, ustic and isohyperthermic. Fifteen soil samples from genetic soil horizons were analyzed for physico-chemical properties. Pedons NNL-P1 and MKG-P1 had loamy sand topsoils overlying sandy loam to sand clay loam subsoils. Pedon NWJ-P1 had sandy clay loam topsoil overlying clay subsoil with indications of eluviation-illuviation as dominant pedogenic process. Whereas pedons NWJ-P1 and MKG-P1 were medium acid to slightly acid (pH 5.91 - 6.35), pedon NNL-P1 was extremely to very strongly acid (pH 4.36 - 4.57). Topsoil OC contents of the soils were very low to medium (0.49 to 1.28%) while subsoil values were very low to low (0.16 - 0.66%). Total nitrogen in the pedons were very low (0.02 - 0.07%) while C/N ratios generally ranged from 7 to 18 indicating good to moderate quality of soil organic matter. All studied soils were low in -1 -1 available P (< 7 mg kg ) except topsoil of pedon NNL-P1 which had medium values (P range 7- 20 mg kg ). CEC values ranged from very -1 -1 low (< 6.0 cmol (c) kg ) to low (6.0 - 12.0 cmol (c) kg ). % base saturation of pedon NNL-P1 was medium (21 - 60) while pedons NWJ-P1 and MKG-P1 had high values (> 60%). Nutrient ratios Ca/TEB, Mg/K and %( K/TEB) indicated some degree of nutrient imbalance in the soils likely to impair nutrient availability to plants. According to USDA Soil Taxonomy the pedons classified as Typic Dystrustepts (pedon NNL- P1), Typic Argiustolls (pedon NWJ-P1) and Typic Haplustepts (pedon MKG-P1) which, according to WRB for Soil Resources, translated into Dystric Cambisols, Luvic Phaeozems, and Eutric Chromic Cambisols, respectively. In view of the study results, the studied pedons differed markedly in terms of pedological and physico-chemical properties, emphasizing the need to characterize soils before embarking on strategies and practices on soil fertility management for enhanced sustainable agriculture production. Sustainable cropping on the studied soils could be achieved with introduction of technologies suitable for rejuvenating soil fertility such as manuring, crop rotation, proper management of crop residues, fallow periods, introduction of leguminous cover crops in the farming system and use of fertilizers, particularly non-acidifying types of fertilizers.