horticulturae Article Organic Materials and Their Chemically Extracted Humic and Fulvic Acids as Potential Soil Amendments for Faba Bean Cultivation in Soils with Varying CaCO 3 Contents Ihab M. Farid 1 , Mohamed A. El-Ghozoli 2 , Mohamed H. H. Abbas 1, * , Dalia S. El-Atrony 1,2 , Hassan H. Abbas 1 , Mohamed Elsadek 3,4 , Hosam A. Saad 5 , Nihal El Nahhas 6 and Ibrahim Mohamed 1, *   Citation: M. Farid, I.; A. El-Ghozoli, M.; H. H. Abbas, M.; S. El-Atrony, D.; Abbas, H.H.; Elsadek, M.; A. Saad, H.; El Nahhas, N.; Mohamed, I. Organic Materials and Their Chemically Extracted Humic and Fulvic Acids as Potential Soil Amendments for Faba Bean Cultivation in Soils with Varying CaCO 3 Contents. Horticulturae 2021, 7, 205. https://doi.org/10.3390/ horticulturae7080205 Academic Editors: Arcângelo Loss, Cledimar Rogério Lourenzi, Paulo Ademar Avelar Ferreira, Moreno Toselli and Gustavo Brunetto Received: 29 June 2021 Accepted: 15 July 2021 Published: 21 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Soils and Water Department, Faculty of Agriculture, Benha University, Toukh 13736, Egypt; ehab.farid@fagr.bu.edu.eg (I.M.F.); dalia_tcrar@yahoo.com (D.S.E.-A.); hharsalem@yahoo.com (H.H.A.) 2 Soils, Water and Environment Research Institute, Agricultural Research Center (ARC), Giza 12112, Egypt; elghozoli_acr@yahoo.com 3 Department of Horticulture, Faculty of Agriculture, Suez Canal University, Ismailia 41522, Egypt; elsadek_m@tongji.edu.cn 4 Department of Landscape Architecture, College of Architecture and Urban Planning, Tongji University, Shanghai 200092, China 5 Department of Chemistry, College of Science, Taif University, P.O. Box 11099, Taif 21944, Saudi Arabia; h.saad@tu.edu.sa 6 Department of Botany and Microbiology, Faculty of Science, Alexandria University, Alexandria 21515, Egypt; nihal.elnahhas@alexu.edu.eg * Correspondence: mohamed.abbas@fagr.bu.edu.eg (M.H.H.A.); ibrahim.ali@fagr.bu.edu.eg (I.M.) Abstract: Organic amendments are important sources of nutrients that release upon organic matter degradation, yet the stability of these organics in arid and semi-arid regions is relatively low. In contrast, humic substances (HS) are resistant to biodegradation and can keep nutrients in the soil available for the plant over a long time. Combinations between humic substances (HS) and mineral- N fertilizers are assumed to retain higher available nutrients in soils than those recorded for the sole application of either mineral or organic applications. We anticipate, however, that humic substances might not be as efficient as the organics from which they were extracted in increasing NP uptake by plants. To test these assumptions, faba bean was planted in a pot experiment under greenhouse conditions following a complete randomized design while considering three factors: two soils (calcareous and non-calcareous, Factor A), two organics (biogas and compost, Factor B) and combinations of the organics and their extracts (HA or FA) together with complementary doses of mineral-N ((NH4) 2 SO 4 ) to attain a total rate of 50 kg N ha −1 (the recommended dose for faba bean plants) (Factor C). Results indicated that nitrogenase activity increased significantly due to the application of the used organics. In this respect, compost manure caused higher nitrogenase activity than biogas manure did. Humic substances raised NP-availability and the uptake by plants significantly; however, the values of increase were lower than those that occurred due to the compost or biogas manure. Moreover, the sole application of the used organics recorded the highest increases in plant biomass. Significant correlations were also detected between NP-availability, uptake and plant biomass. This means that HS could probably retain nutrients in available forms for long time periods, yet nutrients released continuously but slowly upon decomposition of organics seemed more important for plant nutrition. Keywords: humic substances; sandy soils; faba bean; NP-uptake; NP-availability 1. Introduction Faba bean (Vicia faba L.) is an important legume crop in Egypt [1] that belongs to the family Fabaceae [2]. Its seeds are the edible parts that may partially replace meat and dairy products in the human diet [3] because they are rich in complex carbohydrates, proteins, Horticulturae 2021, 7, 205. https://doi.org/10.3390/horticulturae7080205 https://www.mdpi.com/journal/horticulturae