Citation: Asif, M.; Haider, M.S.; Akhter, A. Impact of Biochar on Fusarium Wilt of Cotton and the Dynamics of Soil Microbial Community. Sustainability 2023, 15, 12936. https://doi.org/10.3390/ su151712936 Academic Editor: Chenggang Gu Received: 31 July 2023 Revised: 19 August 2023 Accepted: 24 August 2023 Published: 28 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Impact of Biochar on Fusarium Wilt of Cotton and the Dynamics of Soil Microbial Community Mamoona Asif, Muhammad Saleem Haider and Adnan Akhter * Department of Plant Pathology, Faculty of Agricultural Sciences, Quaid-e-Azam Campus, University of the Punjab, Lahore P.O. Box 54590, Pakistan; mamoona.rehan@gmail.com (M.A.); dean.fas@pu.edu.pk (M.S.H.) * Correspondence: adnanakhter.iags@pu.edu.pk Abstract: The effects of biochar on leaf and soil-borne diseases of plants can be seen in addition to its ability to sequester carbon, improve soil quality, and enhance plant performance. However, the mechanisms by which soil-borne pathogens are suppressed and plant performance is enhanced are not well understood. The present work aims to comprehensively establish the links between biochar-induced changes in the richness of the rhizosphere microbial population, in association with the reduction of soil-borne Fusarium wilt disease (Fusarium oxysporum f. sp. vasinfectum), in cotton (Gossypium hirsutum), with improved plant performance. Biochar made from organic waste significantly decreased the colonization and survival of Fusarium in soil, raised the culture-able counts of numerous microbes with biocontrol potential (microorganisms that boost plant growth and development), and inhibited Fusarium wilt of cotton. The biochar amendment significantly enhanced the cotton plant development and physiological parameters such as chlorophyll content, etc. Overall, 9% organic waste biochar had shown a significant impact on cotton growth as compared to other treatments with or without biochar. Compared to the soil-only control, the disease index was considerably reduced in all biochar-amended treatments. In terms of the plant’s resistance to Fusarium wilt, biochar-induced increases in the level of overall chlorophyll content and biochemicals such as phenolics, flavonoids, etc. Additionally, cotton plants grown with a 9% biochar composition had considerably greater NPK levels than other treatments with or without biochar. The biochar addition resulted in increased counts of Pseudomonas spp., Actinomycetes spp., and Trichoderma spp., while Acidobacteriales, Rhodospirillales, and Frankiales were less when compared with an un-amended (without biochar) soil control. Thus, the composition of rhizosphere bacteria in the treatments with and without modified biochar was found to differ significantly. Keywords: disease protection; Fusarium oxysporum f. sp. vasinfectum; microbial biodiversity; defense chemicals 1. Introduction Emissions of greenhouse gases need to be decreased if we are going to combat global warming. Pollution caused by fossil fuels is the main cause of the anthropogenic greenhouse effect, making a decrease in the usage of fossil fuels a top concern [1]. Yet, a responsible plan also includes actively removing carbon dioxide from the atmosphere because some emissions will be inevitable [2]. Such carbon sequestration confronts a variety of difficulties, including the need for a long-term, significant net removal of carbon dioxide. For the soil to retain its chemical, physical, and biological integrity to carry out its agricultural production and environmental functions, a certain level of organic matter must be maintained in the soil [3]. Attention has also been drawn to the idea that adding biochar to soil could be a way to control plant diseases. Biochar sequestration is a short-term solution that can balance the increasing production of carbon. It is a renewable energy technique that sequesters carbon and decreases emissions when paired with bioenergy generation [4]. Growing plants that store carbon dioxide in their biomass or in soil organic matter is an established method of Sustainability 2023, 15, 12936. https://doi.org/10.3390/su151712936 https://www.mdpi.com/journal/sustainability