Environmental Impacts of Farm Waste Treatment Methods and Perspectives of Valorization by Composting: The Case of the Farm “Sociétéde Provenderies du Cameroun (SPC)” of Foumbot

Waste recovery is an environmental, agronomic and economic asset. The farm “Société de Provenderies du Cameroun” (SPC) processes its wastes by incineration and landfill. During this study, environmental impacts of these two treatment methods were assessed in this farm and a composting experiment was also conducted. For the experiment, chicken carcasses and droppings mixed with wood shavings, straw, incineration ash, egg shells and cattle dung were distributed differently in four experimental composters C1, C2, C3 and C4 with the same starting weight. C1 consisted of the first three waste types, for C2, C3 and C4 a new waste was added in the order they are listed above. The results show that the major impacts associated with the incineration and landfilling of SPC waste are the degradation of the health of workers and surrounding populations, the occurrence of conflicts, and the pollution of the air, soil and groundwater of the site. As far as composting is concerned, the characteristics of three of the four composts obtained are usable as soil fertilisers. Indeed, at the end of the experiment, the pH of the four composters was basic (8), the temperature values were between 24°C and 34°C and the humidity values were between 37% and 41%. However, the last parameter, the C/N ratio, was not satisfactory for C1 (13.42), which eliminated it from mature and ready-to-use composts according to FAO standards. The C/N ratios of C2 (15.71), C3 (16.30), and C4 (18) composters were found to be good for mature and ready-to-use compost.

Effect of Land Use Management Patterns on Mineralization Kinetics of Soil Organic Carbon in Mount Bambouto Caldera Area of Cameroon

Soil organic carbon (SOC) mineralization was carried out on soil samples collected from two depths: 0 - 20 cm and 20 - 40 cm for all land use (LU) types (grasslands, croplands, natural forest/fallow lands, cocoa/palm plantations, and settlement/agro-forests). Microbiological analyses were carried out by measuring microbial activity in 40 g of dried soil samples wetted to 60% water holding capacity and incubated at 27 °C. Carbon dioxide (CO2) emission was measured for 10 weeks using a CO2 trap. Descriptive and graphical analyses of CO2 respiration were done using CO2 emission data. Models were developed to describe CO2 respiration and the first order kinetic model provided best fit to C-mineralization. Potentially mineralizable carbon (Co) and C-mineralization rate were higher in grasslands than other LU types, indicating a higher rate of microbial activity and carbon cycling. Metabolic quotient was higher in forest/fallow lands and reflects greater stress of the microbial community and a high requirement of maintenance energy. Grasslands enhanced more SOC accumulation and decomposition, suggesting a better carbon sink than other land use and management systems (LUMS). Microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) varied across LU patterns with maximum values in grasslands and minimum values in natural forest/fallow lands insinuating better soil quality for grasslands. MBC and SOC positively correlated with Co and C-mineralization, which intimates that C-mineralization is influenced by availability of MBC and SOC. Metabolic quotient (qCO2) negatively correlated with microbial quotient (MBC:SOC), depicting that higher values of qCO2 signify difficulties in using organic substrates during microbial activity as a result of low MBC:SOC. Changes in LUMS affected the mineralization kinetics of SOC in the study area.

Application of Black Soldier Fly Frass, Hermetia illucens (Diptera: Stratiomyidae) as Sustainable Organic Fertilizer for Lettuce, Lactuca sativa Production

In recent years, black soldier fly (BSF) has been shown to efficiently convert organic waste into nutrient-rich larval biomass while generating frass as the main by-product. This work aims to investigate the potential of BSF frass (BSFF) as an organic fertilizer for agricultural production. BSFF was produced by recycling household waste using BSF larvae, and a portion was taken to the lab for physicochemical and microbial analyses before the field trial on lettuce growth and health. The field trial consisted of two doses of BSFF (15 t·ha-1 and 30 t·ha-1) and one dose of urea (0.214 t·ha-1). An unfertilized plot was prepared and used as a control, and the effects on lettuce growth were assessed using agronomic parameters while the health effects were assessed using parameters such as: the number of leaves affected per plant, the incidence of affection, the severity of the affection and the microbial analysis. BSFF exhibited acceptable physicochemical properties as an organic fertilizer. Its application improved the growth parameters of lettuce plants compared to urea and control. The application rates of 15 t·ha-1 and 30 t·ha-1 did not reveal any significant difference (p > 0.05). Further studies are therefore needed to determine the minimum applicable dose. The health parameters of the lettuce plants were slightly altered regardless of the treatment and the microbial analysis of the affected leaves revealed pathogenic microorganisms. We therefore recommend that decontamination methods be considered when producing BSFF as an organic fertilizer.