SEGH Articles

# SEGH2018 Prize Winners Series: Nswana Kafwamfwa

10 August 2018
Winner of a Best Poster Prize at SEGH2018: On-farm assessment of carbon stocks under sub-optimal and optimal input CA management in Mpongwe and Chisamba districts of Zambia - this installment of the Prize Winners Series is contributed by Nswana Kafwamfwa.

Kafwamfwa N., 2Chabala L. and 2Shepande C.

1.Zambia Agriculture Research Institute, Soils and Water Management Section., 2.The University of Zambia, School of Agricultural Sciences

Corresponding author: knswana@yahoo.com, chitalu81.nk@gmail.com

Conservation Agriculture (CA) is one of the promising practices being promoted for reducing the greenhouse gas effect in the face of climate change. This study sought to assess the amount of soil organic carbon (SOC) in CA and Conventional Tillage (CT) cropping systems under suboptimal and optimal input management in Mpongwe and Chisamba (GART) districts of Zambia. In the context of this study, optimal input management refers to agricultural production management were maximum available inputs are applied to the field while, suboptimal input management refers to management were the farmers use a blanket recommendation of inputs per hectare, e.g blanket fertilizer recommendation of four top and four basal fertilizers per hectare at small scale farmer level in Zambia. Composite soil samples were randomly collected at a depth of 20 cm to assess the C-stock in fields which have been under CA/CT between 3 and 7 years under suboptimal input management and between 12 and 18 years under optimal input management.

Kafwamfwa conducting soil sampling for the research project

Changes on selected soil properties over time were determined using standard laboratory procedures. The amount of soil carbon sequestered was assessed using the adjusted Land Use, Land-Use Change and Forestry (LULUCF) model. The results indicate that Conservation Agriculture (CA) fields had sequestered 1,424 kg SOC /ha,year while the Conventional Tillage (CT) fields had 392 kg SOC/ha,year, representing a threefold difference. At Golden valley Agriculture Research Trust (GART), SOC was 63,180 kg/ha after 15 years of CA compared to 50,622 kg/ha under CT over the same period. These findings suggest that CA can mitigate the effects of climate change by reducing the carbon emission resulting from the crop production practices. Further, there were significant differences between C-stocks under the 18 and 12 years CA fields under faidherbia albida (Musangu) trees at GART. The results also showed increased pH values under the eucalyptus field compared to the other fields at GART suggesting that pH increases when land use is changed from agriculture to forestry.

Kafwamfwa at the 34th International Conference of SEGH in Livingstone, Zambia

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Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Distribution of metal(loid)s in particle size fraction in urban soil and street dust: influence of population density 2020-01-18

### Abstract

Assessment of street dust is an invaluable approach for monitoring atmospheric pollution. Little information is available on the size distribution of contaminants in street dusts and urban soils, and it is not known how the population density would influence them. This research was carried out to assess the size distribution of trace metal(loid)s in street dust and urban soil, and to understand how population density might influence the size-resolved concentration of metal(loid)s. Three urban areas with a high, medium and low population density and a natural area were selected and urban soil and street dust sampled. They were fractionated into 8 size fractions: 2000–850, 850–180, 180–106, 106–50, 50–20, 20–10, 10–2, and < 2 µm. The concentration of Pb, Zn, Cu, Cd, Cr, Ni, As, and Fe was determined, and enrichment factor and grain size fraction loadings were computed. The results indicated that the concentration of Pb, Zn, Cu, Cd, and Cr was highly size dependent, particularly for particles < 100 µm, especially for street dust. Low concentrations of Ni and As in street dust and urban soil were size and population density independent. Higher size dependency of the metals concentration and the higher degree of elemental enrichment in the street dust fractions than the urban soils indicate higher contribution of human-induced pollution to the dust. Findings also confirm the inevitability of size fractionation when soils or dusts are environmentally assessed, particularly in moderately to highly polluted areas. Otherwise, higher concentrations of certain pollutants in fine-sized particles might be overlooked leading to inappropriate decisions for environmental remediation.

• Soil–plant system and potential human health risk of Chinese cabbage and oregano growing in soils from Mn- and Fe-abandoned mines: microcosm assay 2020-01-17

### Abstract

In Portugal, many abandoned mines are often close to agricultural areas and might be used for plant food cultivation. Soils in the vicinity of two Mn- and Fe-abandoned mines (Ferragudo and Rosalgar, SW of Portugal) were collected to cultivate two different food species (Brassica rapa subsp. pekinensis (Lour.) Hanelt and Origanum vulgare L.). Chemical characterization of the soil–plant system and potential risk of adverse effects for human health posed by plants associated with soil contamination, based on the estimation of hazard quotient (HQ), were assessed in a microcosm assay under greenhouse conditions. In both soils, the average total concentrations of Fe and Mn were above the normal values for soils in the region and their concentration in shoots of both species was very high. Brassica rapa subsp. pekinensis grew better in Ferragudo than in Rosalgar soils, and it behaved as an excluder of Cu, Mn, Fe, S and Zn in both soils. The HQ for Cu, Fe, Mn and Zn in the studied species grown on both soils was lower than unit indicating that its consumption is safe. The high Mn tolerance found in both species might be due in part to the high contents of Fe in the soil available fraction that might contribute to an antagonism effect in the uptake and translocation of Mn. The obtained results emphasize the need of further studies with different food crops before cultivation in the studied soils to assess health risks associated with high metal intake.

• Concentration, fractionation, and ecological risk assessment of heavy metals and phosphorus in surface sediments from lakes in N. Greece 2020-01-13

### Abstract

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, were investigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index Igeo values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as “unpolluted,” while many sediments in lakes Volvi and Kerkini were characterized as “moderately to heavily polluted” with regard to Cd. The descending order of potential ecological risk $$E_{\text{r}}^{i}$$ was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.