Make a choice: A rapid strategy for minimizing peat in horticultural press pots substrates using a constrained mixture design and surface response approach

PLOS ONE RESEARCH ARTICLE Make a choice: A rapid strategy for minimizing peat in horticultural press pots substrates using a constrained mixture design and surface response approach André Sradnick ID*, Marie Werner, Oliver Körner ID Leibniz Institute for Vegetable and Ornamental Crops (IGZ) e.V., Grossbeeren, Germany a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Sradnick A, Werner M, Körner O (2023) Make a choice: A rapid strategy for minimizing peat in horticultural press pots substrates using a constrained mixture design and surface response approach. PLoS ONE 18(7): e0289320. https://doi. org/10.1371/journal.pone.0289320 Editor: Randall P. Niedz, United States Department of Agriculture, UNITED STATES Received: March 27, 2023 Accepted: July 16, 2023 Published: July 31, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0289320 Copyright: © 2023 Sradnick et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript and its Supporting information files. * Abstract Peat is the most common used substrate in horticultural seedling production. To reduce peat in horticultural potted plant cultivation systems in general is an obstacle, even within the highly specialized horticultural industry. Next to soil-less cultivation systems as e.g. hydroponics, the horticultural industry is eagerly looking for suitable peat substitutes. The demands on these compounds are high, basically mimicking the physical properties of peat. A 100% replacement of peat for press-pots used in seedling production has not yet been found, and only mixes of peat and substrates exist. Several suitable peat substitutes with different properties are known, that usually are used as a share of a mixed peat-substitute substrate. A constrained mixture design was used to test substrates containing 50% v/v and 25% v/v peat and four peat substitutes (two composts and two wood fibers) for vegetable seedling production. By limiting the maximum quantities of each material to be added, there was no negative effect on the growth of Chinese cabbage (Brassica rapa subsp. pekinensis). This means a reduction in of peat to 25% v/v is possible without a change in substrate quality. The mixture design allowed a quick decision to be made regarding the most suitable peat-reduced mixtures. The surface response approach enabled the experimental results to be easily transferred to horticultural practices, additionally. This flexible and efficient method also allows the predictions to be used to meet specific crop management needs. Introduction Currently, approximately 38% of peat produced in Europe is used for non-energy purposes [1]. The horticultural sector accounts for a significant portion of this usage, at approximately 65% [2]. Peatlands are essential natural carbon sinks due to their capability of storing substantial amounts of carbon dioxide (CO2-C). However, when peat is used as a seedling substrate in nurseries, additional CO2-C is emitted as the organic matter is mineralized at a rate of 5% per year [1] and thus contributes to the input of greenhouse gases into the atmosphere [3]. Furthermore, the peat extraction process disrupts the peatland ecosystem in a sustainable manner [4]. PLOS ONE | https://doi.org/10.1371/journal.pone.0289320 July 31, 2023 1 / 19 PLOS ONE Funding: Funding for the research was provided by the German Federal Ministry of Food and Agriculture (BMEL) through the project “Development and evaluation of peat-reduced production systems in horticulture (ToPGa)” (project 2220MT006C). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. A strategy for minimizing peat in horticultural using an constrained mix design and surface response approach The challenge of reducing the use of peat in European horticulture has been acknowledged, with many countries ratifying sustainable peat reduction targets [1]. This implies that peatbased soilless systems, commonly employed in horticulture, may need to be re-evaluated in terms of their water supply and nutrient management [5]. Moreover, it has been projected that the demand for substrates may significantly increase in the coming decades [6]. In order to address the aforementioned challenges, peat-reduced or peat-free substrates must continue to provide the necessary technological requirements to be compatible with highly automated horticultural companies. This is particularly pertinent to ensure consistent substrate quality and meet the specific requirements for various horticultural sectors such as ornamental plants, herbs, woody plants, soft fruit and nursery plants. Peat is commonly replaced with regenerative organic materials such as compost, fermentation residues, wood fibers, fiber plants, sphagnum moss, or coconut fiber [7–10]. However, may not be suitable as sole peat substitutes, either because their inability to meet physical, biological, and chemical requirements, or because they cannot meet practical demands in terms of availability. In the horticultural industry, mixtures are utilized for the purpose of achieving desired qualities [5]. Compost can be an important replacement for peat due to its wide availability. During composting, organic material is transformed microbiologically through aerobic processes, resulting in an improvement in several of its properties, making it a suitable substrate [11]. Green compost is highly compatible due to its low salt content compared to other composts [12]. However, compost may have often a pH above 7, which limits its use as a peat substitute aggregate. Wood fiber has been used in multiple sources as an alternative to peat [13–15]. Similarly to compost, it is currently obtainable in sufficient quantities. The use of fibrous materials derived from wood or fibrous plants is suitable as a peat substitute, particularly due to its low salt concentration and advantageous hydrological characteristics. Nonetheless, its usage is constrained by high nitrogen immobilization potential [13]. Research into potential substitutes for peat has been ongoing for decades [16]. The majority of research into peat alternatives does not explore whether peat can be replaced, but instead what percentage, what proportions and what materials are suitable for substitution [17–20]. Various sources suggest that a mixture (...truncated)