Fertiliser effect on Swiss chard of black soldier fly larvae-frass compost made from food waste and faeces

Inadequate organic waste management can have adverse health effects and pollute the environment. If the energy and nutrients in organic waste were to be used efficiently, they could increase food security. Composting using black soldier fly (BSF) larvae can convert organic waste into two valuable products: organic fertiliser, in the form of treatment residues, and animal feed protein, in the form of larvae. To demonstrate the feasibility of using BSF treatment residues as organic fertiliser, more knowledge is needed about the effect of BSF larvae-frass compost on plant growth and performance. This study examined the effect on growth of Swiss chard of five fertiliser treatments: (1) BSF larvae-frass compost of human faeces (BSF-F); (2) BSF larvae-frass compost of food waste (BSF-FW); (3) cow manure (CM), the most commonly used organic fertiliser globally; (4) an inorganic fertiliser containing nitrogen, phosphorus and potassium (NPK); and (5) a negative control with no fertiliser. The results revealed that BSF larvae-frass compost of human faeces and food waste gave comparable yields to inorganic fertilisers, and significantly higher yields than the unfertilised control. The percentage increase in fresh weight of leaves in the treatments compared to the unfertilised control were 132% for BSF-FW, 115% for BSF-F, 118% for NPK and 86% for CM. Principal component analysis (PCA) showed that all treatments involving fertiliser gave differences in soil nutrient concentrations. PCA also revealed a positive correlation between soil nitrate concentration and yield. Thus, using BSF larvae-frass compost as fertiliser could be a way of efficiently returning plant nutrients in faeces and organic waste to the food chain.