Investigating the effects of fish effluents as organic fertilisers on onion (Allium cepa) yield, soil nutrients, and soil microbiome

•Soil fertility was enhanced by the addition of fish effluents.•Fertilisation with fish effluents resulted in higher plant yields than manure.•Manure resulted in a higher species diversity compared with fish effluents.•Soil microbial species number increased after fish effluent supplementation.•The fish effluents’ superiority questions their prohibition in organic agriculture.