ORIGINAL RESEARCH International Journal of Recycling of Organic Waste in Agriculture (2021)10: 415-426 Doi: 10.30486/IJROWA.2021.1899855.1073 Effects of organic manures bioremediation on growth performance of Maize (Zea mays L.) in crude oil polluted soil Stella Eberechukwu Obasi 1* , Nwogo Ajuka Obasi 2 , Ephraim O Nwankwo 3 , Benneth Nnanyelugo Enemchukwu 1 , Robert Ikechukwu Igbolekwu 1 , Jeff Onochie Nkama 1 Received: 13 May 2020 / Accepted: 06 July 2021 / Published online: 06 November 2021 Abstract Purpose Crude oil pollution adversely affects the environment and its remediation presents significant challenge due to its complex nature. Bioremediation approaches have proved effective and the use of organic wastes makes the process eco-friendly. Therefore, this study investigated the effects of organic manures amendments of crude oil polluted soil on the growth and performance of maize (Zea mays L.) under potted environment at the botanic garden of University of Port-Harcourt, Nigeria. Method The loamy soils in different pots (5.0 kg each) were polluted with crude oil in six factorial treatments set (0.0%, 2.0%, 4.0%, 6.0%, 8.0% and 10.0%) and allowed for two weeks. Thereafter, the polluted soils were sub- jected to different organic manure amendment: poultry-manure, cow-dung, saw-dust, combined poultry-manure + cow-dung, combined poultry-manure + saw-dust and combined cow-dung + saw-dust manures with two sets of control: polluted soil + no organic manure and non-polluted soil + no organic manure. The amended soils were allowed for two weeks before sowing viable maize seeds and the seedling monitored every two weeks after ger- mination for a period of eight weeks. Results Crude oil pollution impaired the maize seed germination, growth and development. Organic manures amendments of polluted-soil significantly improved (P < 0.05) maize plant agronomic characteristics with com- bined manures especially poultry-manure + cow-dung showing highest improvement than other combined or sin- gle manure treatment. Conclusion Combined organic manures amendments of crude oil polluted soil especially cow-dung + saw-dust were found to be environmentally friendly and beneficial for maize crop production. Keywords Crude oil pollution, Waste management, Zea mays L., Bioremediation, Crop production, Agronomic characteristics Plant Ecology Research Unit, Department of Science Laboratory Technology, School of Science, Akanu Ibiam Federal Polytechnic Unwana, Ebonyi State, Nigeria Environmental Biochemistry, Health and Toxicology Research Unit, Department of Medical Biochemistry, Alex Ekwueme Federal Uni- versity Ndufu-Alike, Ebonyi State, Nigeria Department of Applied Biology, Faculty of Biological Science Ebo- nyi State University, Abakaliki, Ebonyi State, Nigeria 1 2 3  Stella Eberechukwu Obasi stellaeobasi@gmail.com Introduction Crude oil spillage occurs regularly in the Niger Delta region of Nigeria where over 80% of the crude oil is produced. In Nigeria, numerous oil fields, tank farms, flow stations, pipelines, tankers and loading jetties constantly cause crude oil pollution especially in Niger Delta areas (Chikere and Chijioke-Osuji 2006; Bebeteidoh et al. 2020). These oil spillages introduce various organic and inorganic chemicals, some of which are non-carcinogenic (growth-inhibiting) and others carcinogenic chemicals, to the environment with direct impact on microorganisms, plants and humans (Okpokwasili and Odokuma 1990; Njoku et al. 2009; Aboh and Isitekhale 2013). Crude oil pollution adversely and drastically affects soil physicochemical properties and many studies (Baker and Herson 1994; Okolo et al. 2005; Liang et al. 2012) have reported its adverse effects on soil ecosystem to include but not limited to absorption to soil particles, provision of an excess carbon that might be unavailable for microbial