Horticulturae 2023, 9, 687. https://doi.org/10.3390/horticulturae9060687 www.mdpi.com/journal/horticulturae Article Nanobiochar Application in Combination with Mulching Improves Metabolites and Curd Quality Traits in Caulifower Naiwen Xue 1,2 , Sumera Anwar 3,4, *, Fahad Shafq 5, *, Gul-e-Kainat 6 , Kaleem Ullah 7 , Muhammad Zulqarnain 8 , Imtiaz Haider 8 and Muhammad Ashraf 6 1 College of Agronomy and Life Sciences, Shanxi Datong University, Datong 037009, China; xuenaiwen920@126.com 2 Facility Agriculture Research and Development Center, Shanxi Datong University, Datong 037009, China 3 Department of Botany, Government College Women University Faisalabad, Faisalabad 38000, Pakistan 4 Department of Bioscience, Durham University, Durham DH1 3LE, UK 5 Department of Botany, Government College University Lahore, Lahore 54000, Pakistan 6 Institute of Molecular Biology and Biotechnology, The University of Lahore, Lahore 54590, Pakistan; gullkainat865@gmail.com (G.-e.-K.) 7 Department of Entomology, Faculty of Agricultural Sciences, University of Punjab, Lahore 54590, Pakistan; muhammad1kaleem.3@gmail.com 8 Department of Agronomy, Faculty of Agricultural Sciences, University of Punjab, Lahore 54590, Pakistan; muhammadzulqarnain1221@gmail.com (M.Z.); imtiaz.haider.1999@gmail.com (I.H.) * Correspondence: anwer_sumera@yahoo.com (S.A.); fahadsheikh@gcu.edu.pk (F.S.) Abstract: Sustainable nutrient management approaches could improve production and quality without afecting soil health. We conducted a feld experiment to investigate the interactive efects of mulching (no mulch, plastic mulch, and straw mulch) and nanobiochar (NBC) foliar application on biomass, nutrient contents, and metabolites in the leaf and curd of caulifower (Brassica oleracea var. botrytis). After 20 days of transplantation, NBC (0.1% w/v) was applied as a foliar spray for four consecutive weeks (one spray per week). At the curd initiation stage, changes in chlorophyll, carot- enoids, and metabolite concentrations in leaves and curd were determined. The application of nano- biochar signifcantly enhanced the curd weight and improved curd morphology. Yield traits includ- ing curd weight, curd diameter, basal diameter, and stalk length were increased by 30, 13, 16, and 20% by NBC application compared to control. Plastic mulching also increased the aboveground biomass by 32% when compared to no mulching. Moreover, plastic mulching and nanobiochar prominently enhanced root dry weight, curd weight, rough solidity index, total soluble sugar in leaf and curd, calcium in curd, and potassium in leaf and curd of caulifower. Overall, this study re- vealed the potential of the foliar application of NBC in promoting the biomass and nutritional prop- erties of caulifower. Keywords: caulifower; mulching; metabolites; nanobiochar; nanoparticles; yield 1. Introduction Excessive application of chemical fertilizers is an inefective practice that alters plant nutrient use efciency [1,2]. Additionally, a large fraction of chemical fertilizers that are not taken up by the plants enter the water table and causes environmental pollution [3,4]. The release of nitrous oxide is another negative aspect to consider that is a major contrib- utor to climate change [5]. Alternatively, increasing crop production while maintaining environmental security could only be possible by promoting sustainable agroecological practices [4,6,7]. Mulching is a sustainable practice to minimize soil salinity, weed germination, and soil erosion and to increase soil organic mater and soil moisture [8,9]. Various mulching materials are normally derived from organic agricultural and industrial waste and animal Citation: Xue, N.; Anwar, S.; Shafq, F.; Gul -e-Kainat, G.; Ullah, K.; Zulqarnain, M.; Haider, I.; Ashraf, M. Nanobiochar Application in Combination with Mulching Improves Metabolites and Curd Quality Traits in Caulifower. Horticulturae 2023, 9, 687. htps:// doi.org/10.3390/horticulturae9060687 Academic Editor: Rita Maggini Received: 8 May 2023 Revised: 28 May 2023 Accepted: 7 June 2023 Published: 9 June 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Atribution (CC BY) license (htps://creativecommons.org/license s/by/4.0/).