  Citation: Sipayung, H.N.; Wu, K.-T.; Liu, D.-Y.; Chen, C.-T. Growth Enhancement of Camellia sinensis with Biochar. Processes 2022, 10, 199. https://doi.org/10.3390/pr10020199 Academic Editor: Avelino Núñez-Delgado Received: 26 December 2021 Accepted: 17 January 2022 Published: 21 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). processes Article Growth Enhancement of Camellia sinensis with Biochar Herta Novalina Sipayung 1 , Keng-Tung Wu 2 , De-Yu Liu 1 and Chien-Teh Chen 1, * 1 Department of Agronomy, National Chung Hsing University, Taichung 402202, Taiwan; hertanovalinas@yahoo.co.id (H.N.S.); ls97649548@icloud.com (D.-Y.L.) 2 Department of Forestry, National Chung Hsing University, Taichung 402202, Taiwan; wukt@dragon.nchu.edu.tw * Correspondence: ctchen41@dragon.nchu.edu.tw; Tel.: +886-4-22840777 (ext. 506) Abstract: Biochar application in the agriculture sector is a practical approach to minimize waste and maintain sustainable farming. However, the information regarding biochar application in tea cultivation is limited and especially rare in field research. In this study, a two-year biochar experiment was conducted in a tea yard subject to tea yield and soil characteristics. According to tea growth, the tea yard for the experiment was divided into weak and normal sectors. Biochar was made from tea processing waste, mainly the twigs. The results showed that biochar application increased tea production by 2.3- and 1.3-fold in the weak and normal sectors, respectively, suggesting that converting tea waste to biochar for soil amendment is beneficial to increasing tea production, particularly in the weak sector. The regression analysis on tea production and soil characteristics revealed that only soil electric conductivity (R 2 = 0.6597), soil organic matter (R 2 = 0.7024), and soil extractable phosphate (R 2 = 0.6547) were positively correlated with tea yield. Therefore, the field experiment of this study improves the understanding of biochar’s agronomic and environmental benefits on plant productivity and soil health. Keywords: biochar; field study; soil amendment; sustainable farming; tea production 1. Introduction Biochar is a pyrolysis product of biomass and is recommended for soil amendment for improving soil health and increasing crop yield [1,2]. The biomass types and pyrolysis conditions were determined by biochar’s structure, nutrient content, pH, and other proper- ties [3–5]. The application of biochar in soil remarkably influenced soil properties, such as enhanced soil water retention, soil aggregation, and nutrient turnover [6–10]. In addition, it was proposed as an efficient process to increase soil organic matters (OM) [2,7,11,12]. Moreover, many reports notified that biochar application affected numerous elements’ cycling in the soil, including carbon (C), phosphorus (P), and nitrogen (N) [13–15]. The soil N and P were preserved due to the addition of biochar [16,17]. Biochar application enhanced the mineralization of preserved soil P and provided a certain proportion for plant uptake [18]. Tea is a worldwide beverage with a yearly yield of 6.5 MT [19], mainly planted in Asia and Africa. The requirements for tea planting were temperatures ranging from 10 to 30 ◦ C, precipitation higher than 1250 mm annually, acidic soils preferably, and 0.5–10 ◦ slopes. Tea production is susceptible to growing seasons and is threatened by extreme climate change. Biochar from the waste of tea drinking has been produced and studied in many reports [20–22]. However, using tea twigs for making biochar has never been studied. Tea twigs are one of the waste materials during tea processing in tea factories, which is around 10% of raw materials. This study recycled the tea processing waste by converting it to biochar and used its benefits as a soil amendment in a tea yard to approach sustainable tea cultivation. The limiting factors of sustainable tea cultivation are soil acidification [23], poor soil fertility [24], and low nutrient efficiency [25]. Soil acidity is one of the most significant Processes 2022, 10, 199. https://doi.org/10.3390/pr10020199 https://www.mdpi.com/journal/processes