Introduction: With urbanization and industrialization in the developing world, urban and peri-urban agriculture is increasingly contributing to urban food systems, employment, and income generation opportunities. However, urbanization and industrialization may release harmful pollutants, including heavy metals and trace elements into agricultural soils, posing ecological, environmental and public health concerns. This paper assessed the potential risks of soil contamination with heavy metals and trace elements in peri-urban farmlands in Nairobi city catchment in Kenya. Methods: A total of 60 soil samples were collected from ten vegetable farming zones (S1-S10) and processed following standard protocols. The concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn were analyzed in the samples using inductively coupled plasma-mass spectrometry (ICP-MS). Results and discussion: Results revealed that the soil samples have elevated concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn, with some elements including As (1.7%), Cd (13.3%), Mn (80%), Pb (1.7%) and Zn (11.7%) exceeding the permissible thresholds for agricultural soils. The spatial distribution of the elements exhibited three similar distribution patterns with slight variations between the hotspot sites of the different elements: (i) Co and Mn, (ii) Cu and Cr and (iii) As, Cd, Fe, Hg, Pb and Zn, while Ni and V exhibited singular spatial distributions compared to other elements. Elements such as As, Cd, Co, Fe, Hg, Mn, Pb and Zn appeared to be of anthropogenic enrichment, while Cr, Cu, Ni and V appeared to originate mainly from lithogenic and natural sources. The elements As, Cd, Hg and Pb exhibited high ecological risks, with Cd contributing about 46-66% of the overall ecological risk. The sampling sites S1, S5, S7, S9 and S10 depicted the highest ecological risks of 145, 103, 146, 121 and 146, respectively. The findings call for proper zoning of suitable agricultural areas and sound waste management protocols in urban and peri-urban landscapes. Further, remediation of contaminated soils and farmers’ sensitization are recommended for ecological and public health risk alleviation.

The increasing global population and the challenges associated with fossil fuel has led to a surge in energy demand, necessitating research on renewable and environmentally friendly energy sources. Biodiesel, is produced from biomass materials like vegetable oil and fats, is a promising alternative. Transesterification is a principal method used in biodiesel production, as it is simple, versatile, and efficient. Biodiesel offers several advantages, including emissions, lubricity, and safety, making it a sustainable fuel option and its properties conforms to the international standards. However, it has lower energy content, cold weather performance issues, and slightly reduced engine power compared to petroleum diesel. The choice of biodiesel feedstock depends on its properties, with jatropha oil and other feedstocks being potential in Ghana. Research on biodiesel in Ghana is still in early stages and the Ghanaian government's policy aims to replace 10 % of petroleum fuel with biofuel by 2020 and 20 % by 2030, but these goals have not been achieved due to barriers. Despite these challenges, the government and stakeholders in the biofuel industry are working to optimize the biodiesel sector for sustainability, efficiency, and scalability. Innovative cultivation techniques and low-cost oil extraction methods are required, necessitating interdisciplinary research collaborations. By capitalizing on these opportunities and implementing targeted interventions, Ghana can become a regional leader in sustainable biodiesel production.

The use of renewable energy as a substitute for fossil fuels has several advantages. For a long time, the growth of Ghana’s renewable energy industry has been a priority for both the past and present governments. Currently, the economic growth of Ghana has not been impressive and the country is entrenched in an energy crisis. Despite the country’s achieving an electrification rate of 80%, still 60% of the rural population have no connection to the electricity service. The review gives an overview of the current energy scenario in Ghana and analyses its potential effects, benefits, and barriers to the expansion of renewable energy sources in the country. The results show that the Ghana Government has established its energy sector based on the definition of the key targets in line with the world trend. Ghana is equipped with a vast quantity of renewable energy potentials which include hydropower, solar, wind, and bioenergy. Even though it is critical to invest in the renewable energy industry, the growth of the sustainable energy sector has been hindered by certain factors such as; insufficient technological knowledge, lack of enough experience in developing sustainable energy and socio-cultural and human barriers.

Soil organic carbon storage in agricultural soil constitutes a crucial potential for sustainable agricultural productivity and climate change mitigation. This paper aimed at assessing soil organic carbon stock and its distribution in three particle size fractions across five cropping systems located in Kiti sub-watershed in Benin. Soil samples were collected using a grid sampling method on four soil depth layers: 0–10, 10–20, 20–30 and 30–40 cm in five cropping systems maize–cotton relay cropping (MCRC), yam–maize intercropping (YMI), teak plantation (TP), 5-year fallow (5YF) and above 10-year fallow (Ab10YF) from July to August 2017. Soil organic carbon stock (C stock) was estimated for the different soil layers and particle-size fractionation of soil organic matter was performed considering three fractions. The fractions coarse particulate organic matter (cPOM: 250–2000 µm), fine particulate organic matter (fPOM: 53–250 µm) and non-particulate organic matter (NOM: <53 µm) were separated from two soil depth layers: 0–10 and 10–20 cm. The results showed that fallow lands Ab10YF and 5YF exhibited the highest C stock, 22.20 and 17.74 Mg C·ha⁻¹, while cultivated land under tillage MCRC depicted the lowest, C stock 11.48 Mg C·ha⁻¹. The three organic carbon fractions showed a significant variation across the cropping systems with the NOM fraction holding the largest contribution to total soil organic carbon for all the cropping systems, ranging between 3.40 and 7.99 g/kg. The cPOM and fPOM were the most influenced by cropping systems with the highest concentration observed in Ab10YF and 5YF. The findings provide insights for upscaling farm management practices towards sustainable agricultural systems with substantial potential for carbon sequestration and climate change mitigation.

Soil quality constitutes a major factor for crops growth. This study aimed at determining the sustainable soil conservation practices that would increase maize growth as well as production and improve the soil moisture. Two experimental sites were chosen: Dan localized on Acrisol and Za- zounmè localized on ferralsol. Two cropping seasons were investigated: the long rain seasons of 2018 and 2019. The experimental design was split-plot with four replications. The main factor was tillage with three modalities: no-tillage (NT); ridging parallel to the slope (PR); Isohypse ridging (IR) and the second factor was mulching with four amounts: 0, 3, 5 and 7 t.ha-1. Tillage, mulch amount and their interaction significantly influenced the soil moisture, maize growth and yield over the two investigated cropping seasons at both sites whereby the highest values were obtained under IR for tillage, 7 t.ha-1 (for mulch amount) and IR7M (for the interaction tillage x mulch amount). Overall, IR significantly increased the maize growth speed by 8% at Dan and by 16% at Za-zounmè; the maize grain yield by 33% at Dan and by 30% at Za-zounmè and the soil water content by 24% at Dan and 20% at Za-zounmè, in comparison with No-Tillage. An increasing effect of mulch amount was also observed. As far as mulching is concerned, the highest values (in average of LR2018 and LR2019) of growth speed (3.77 cm.day-1 at Dan and 4.08 cm.day-1 at Za-zounmè); grain yield (3003.03 at Dan and 3471.09 kg.ha-1 at Za-zounmè) and soil water content (26.89 mm at Dan and 20.44 mm at Za-zounmè) were observed. This suggests that isohypse ridging associated with an appropriate amount of organic mulch could be an option to mitigate dry spells and drought and improve local farmers’ income in the area of low rainfall in sub- Sahara Africa.