Browsing by Author "Mng'ong'o, Marco"

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Assessment of arsenic status and distribution in Usangu agro-ecosystem-Tanzania.
(Elsevier Ltd., 2021-06-09) Mng'ong'o, Marco; Comber, Sean; Munishi, Linus; Blake, William; Ndakidemi, Patrick; Hutchinson, Thomas H
This study was conducted to assess arsenic (As) status and distribution in Usangu agroecosystem-Tanzania, including three land use. About 198 soil samples were collected in ten irrigation schemes in three land uses. Total and bioavailable As were determined by acid digestion (Aqua regia (AQ)) and Mehlich 3 method (M3) to estimate status, distribution and bioavailability. Arsenic concentration were variable among land use and irrigation schemes where total arsenic ranged 567.74-2909.84 μg/kg and bioavailable As ranged 26.17-712.37 μg/kg. About 12-16% of total arsenic were available for plant uptake. Approximately 86.53% of studied agricultural soils had total As concentration above Tanzania maximum allowable limit. Bioavailable As were lower compared to total As and were within the acceptable threshold. Total arsenic concentration were variable among schemes and higher values were observed in schemes which are highly intensified and mechanized. Thus, this study provides essential site specific preliminary baseline information for As status and distribution in agricultural soils to initiate monitoring and management strategies for increased land productivity and environmental safety.
Characterization of soil phosphate status, sorption and saturation in paddy wetlands in usangu basin-Tanzania.
(2021-04-02) Mng'ong'o, Marco; Munishi, Linus K.; Blake, William; Ndakidemi, Patrick A.; Comber, Sean; Hutchinson, Thomas H.
Phosphorus (P) is a vital plant macronutrient required for plant growth which usually available in limited amount. P availability for plant uptake in highly weathered soil is controlled by soil erosion and high fixation. The availability of P applied from fertilizers depend on the soil pH, soil sorption capacity (PSC) and P saturation status (PSD), which determines P storage, losses, fixation, and additional P to be added with minimal loss to the environment. PSC and PSD are agro-environmental indicators used to estimate P availability and P loss to the environment. However, PSC and PSD of agricultural soils had been never studied in Tanzanian soils. This study was conducted to assess and estimate P availability, PSC and PSD and the risks of P losses in tropical soils from Usangu basin popular for paddy farming. In total, 198 soil samples from 10 paddy irrigation schemes were collected (November-December 2019) and analyzed for inherent P (P), metal oxides of Aluminium (Al ), iron (Fe ), and calcium (Ca ) as main PSC and PSD determinant. The determined concentrations were in range of; P 014.9-974.69 mg/kg, Al 234.56-3789.36 mg/kg, Fe 456.78-2980.23 mg/kg, and Ca 234.67-973.34 mg/kg. Estimated PSC ranged 5.62-34.85 mmol/kg with a mean value of 14.14 mmol/kg corresponding to high status, ensuring high P holding capacity for plant uptake. However, some soils had very low PSC creating a risk of P loss to environment. Among soils, the estimated PSD ranged from 0.01 to 17.57% and was below (<24%), indicating low P loss risks to surface and groundwater, however, some soils were observed to have PSD above 15% which correspond to a critical degree of phosphate saturation of 25% in a watershed using oxalate extraction method. Therefore some sites were associated with high P loss to the environment, immediate and precautionary actions for sustainable P management to increase productivity, environmental safety and sustainability are needed to be in place.