Nematology 0 (2021) 1-12 brill.com/nemy Impact of biochar amendment on soil nematode communities in a West African rain-fed rice cropland Segun O. OLADELE 1,∗ , Adebayo ADEYEMO 2 , Moses AWODUN 2 , Ajoke ADEGAYE 2 and Mariko INGOLD 3 1 Department of Agronomy, Faculty of Agriculture, Adekunle Ajasin University, Akungba Akoko, Nigeria 2 Department of Crop, Soil and Pest Management, Federal University of Technology, Akure, Nigeria 3 Section of Organic Plant Production and Agroecosystem Research in the Tropics and Subtropics, University of Kassel, D-37213 Witzenhausen, Germany Received: 9 April 2021; revised: 7 June 2021 Accepted for publication: 8 June 2021 Summary – Nematode population and diversity in a West African rain-fed rice cropland amended with biochar (B), biochar plus inorganic fertiliser (B + NPK), inorganic fertiliser (NPK) and control (CK) without amendments were investigated in a 3-year field study. Results demonstrated that significant differences exist between treatments and years of study for total nematode population and nematode trophic groups. Total nematode density, nematode trophic group (bacterivore and plant-parasitic) density were increased and dominant in B + NPK compared with CK after 3 years. Relative abundance of nematode genera according to trophic group across treatments showed Hirschmanniella (23%) as the dominant plant parasites in NPK, and Heterocephalobus (27%), Aphelenchoides (22%) and Eudorylaimus (9%) as dominant bacterivores, fungivores and omnivores-predators, respectively, in B + NPK. Trophic group indicators showed that the fungivore plus bacterivore to plant-parasitic ratio (73%) was significantly increased by B + NPK treatment in comparison to CK. Conversely, treatments exerted no significant effect on the fungivore to bacterivore ratio (F/B) throughout the period of study, which implies less disturbance and adverse impact of biochar on nematode communities. Apart from treatments and environmental factors, changes in nematode trophic groups were strongly related to soil chemical properties, such as soil pH, total nitrogen and available phosphorus, which shows their influence on soil nematode community. Our result shows the positive effect of integrated addition of biochar and inorganic fertiliser in balancing nematode diversity and building a resilient soil ecosystem in a low input rain-fed rice cropping system. Keywords – below ground biodiversity, food web, organic additives, Oryza sativa, soil fauna. Organic additives (OAs) are widely regarded as recy- cled products derived from plants and animals with poten- tial use as soil conditioners or improver. An example of soil OAs is biochar – a pure carbon dense material derived from the thermal pyrolysis of organic biomass in the presence of little or no oxygen and intended for use as a soil ameliorant (Oladele et al., 2019a, b). Biochar is basically applied to improve degraded soils, enhance water and nutrient retention, mitigate greenhouse gas emissions from agricultural croplands and boost soil func- tioning (Steinbeiss et al., 2009). Many biochar studies have focused on its conditioning effect on soil physico- chemical properties and crop yield (Dias et al., 2010; Gaskin et al., 2010; Zhang et al., 2010; Butnan et al., 2015), and microbial communities and enzymatic activ- ities (Warnock et al., 2007; Deenik et al., 2010; Dempster et al., 2011; Lehmann et al., 2011; Oladele et al., 2019c), while studies on soil faunal response, e.g., nematodes, are scarce. Soil nematodes are one of the most densely popu- lated mesofauna with about five trophic groups occupy- ing consumer levels within the soil food web (Biederman & Boutton, 2009). Nematodes play an important role in soil organic matter cycling and could be used as a bio- indicator of soil health, biota biodiversity and ecosystem sustainability (Hu & Qui, 2010). In addition, soil nema- todes serve as indicators of soil pollution, disturbance, and possible toxic contents of amendments upon incorpo- ration in soils by showing distinct changes in population and diversity (Lehmann et al., 2011). Studies on biochar ∗ Corresponding author, e-mail: segun.oladele@aaua.edu.ng © KONINKLIJKE BRILL NV, LEIDEN, 2021 DOI 10.1163/15685411-bja10121