Citation: Lei, A.-Q.; Yang, Q.-H.; Zhang, Y.; Liao, W.-Y.; Xie,Y.-C.; Srivastava, A.K.; Hashem, A.; Alqahtani, M.D.; Abd − Allah, E.F.; Wu, Q.-S.; et al. Agronomic Practices Alter Regulated Effects of Easily Extractable Glomalin-Related Soil Protein on Fruit Quality and Soil Properties of Satsuma Mandarin. Agronomy 2023, 13, 881. https:// doi.org/10.3390/agronomy13030881 Academic Editor: Salvatore Camposeo Received: 28 February 2023 Revised: 11 March 2023 Accepted: 13 March 2023 Published: 16 March 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/). agronomy Article Agronomic Practices Alter Regulated Effects of Easily Extractable Glomalin-Related Soil Protein on Fruit Quality and Soil Properties of Satsuma Mandarin An-Qi Lei 1 , Qing-Hua Yang 2 , Ying Zhang 2 , Wen-Yue Liao 2 , Ya-Chao Xie 2 , Anoop Kumar Srivastava 3 , Abeer Hashem 4 , Mashael Daghash Alqahtani 5 , Elsayed Fathi Abd_Allah 6 , Qiang-Sheng Wu 1, * and Yi Zhang 1 1 College of Horticulture and Gardening, Yangtze University, Jingzhou 434025, China 2 Yichang Citrus Science Institute, Yichang 443005, China 3 ICAR-Central Citrus Research Institute, Nagpur 440033, India 4 Botany and Microbiology Department, College of Science, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia 5 Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia 6 Plant Production Department, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh 11451, Saudi Arabia * Correspondence: wuqiangsheng@yangtzeu.edu.cn Abstract: Easily extractable glomalin-related soil protein (EEG) released from arbuscular mycorrhizal fungi exhibits many roles in soil and plants, while it is not clear whether the biostimulator alone or in combination with agronomic practices can improve soil characteristics and fruit quality in citrus. The objective of this study was to analyze the effects of foliar sprays of EEG, singly or in combination with fruit bagging (FB), reflective film mulching (RF), and grass-proof cloth mulching (GPC) on root mycorrhizal colonization rate, fruit internal and external quality, and soil structure and fertility on an early-ripening Satsuma mandarin “Oita 4” (Citrus unshiu cv. Oita 4). Exogenous EEG application increased root mycorrhizal colonization, while agronomic practices dramatically inhibited root mycorrhizal colonization in EEG-treated trees. Foliar EEG application significantly improved the internal and external quality of fruits, but the combination of three agronomic practices with EEG did not further enlarge the improved effect on the external quality of fruit and even produced an inhibitory effect. Also, the addition of RF further amplified the improved effect of EEG on the contents of fruit vitamin C and soluble solids. EEG application also significantly elevated sucrose in the fruit pith and juice sac, fructose in the fruit peel, fruit pith, segment membrane, and juice sac, and glucose in the fruit pith, segment membrane, and juice sac. Additional RF treatment could increase sucrose in the fruit peel and juice sac as well as glucose in the fruit peel to varying degrees in EEG-treated trees. EEG application also significantly increased soil organic carbon, mean weight diameter, nitrate nitrogen, ammonium nitrogen, available phosphorus, and available potassium levels, with additional agronomic practices almost reducing the promoting effect of EEG on these soil variables. It has been summarized that a single EEG application had positive effects on fruit quality and soil fertility, while the additional agronomic practices resulted in little change or even suppressed the positive effects of EEG. Keywords: aggregate; glomalin; mycorrhiza; soil organic carbon; sugar 1. Introduction Citrus plants are cultivated in more than 140 countries around the world with an annual production of 124.3 million tons, and its fruits are rich in various ingredients such as carotenoids, vitamins, essential oils, coumarins, sugars, etc. [1]. Satsuma mandarin Agronomy 2023, 13, 881. https://doi.org/10.3390/agronomy13030881 https://www.mdpi.com/journal/agronomy