Agronomic potential of Hermetia illucens frass in the cultivation of ryegrass in distinct soils

Cropping systems are strongly dependent on mineral fertilisers, which are effective in achieving high crop productivities. However, these chemical inputs end up compromising soil quality in the long-term. Frass from black soldier fly (BSF) larvae is a novel organic fertiliser that is rich in organic matter and advocated as a material that can sustain crop productivity while increasing soil quality. This study aimed at evaluating distinct fertilisation regimes in the cultivation of ryegrass (Lolium multiflorum Lam. or annual ryegrass) in soils of different types (sandy, loamy and clay) and fertility levels. In a 7-month pot experiment conducted in a glass greenhouse, plants were cultivated with exclusive mineral (MT) or organic (OT) fertilisation, in addition to combinations between both (mineral and organic, MOTs) in different proportions (25:50; 50:50 and 75:25), considering a 140 kg per hectare N demand. Crop yield was favoured by the combination of organic and mineral fertilisers in all soils, which also had its fertility increased, especially regarding organic matter build-up and nutrient accumulation. In addition, the presence of frass in the sandy soil stimulated microbial activity, which was measured by the enzyme dehydrogenase. Frass derived from BSF larvae can be considered an adequate organic fertiliser in the cultivation of ryegrass in distinct soil types, when applied in partial (25% to 75%) replacement of mineral fertilisers, enabling high crop productivity and nutritional quality of the crop, while increasing soil fertility.