Special Issue "Advances in Soilless Substrate Science for Modern Plant Production Systems"

A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Horticultural and Floricultural Crops".

Deadline for manuscript submissions: closed (15 July 2021).

Special Issue Editors

Dr. William Carl Fonteno III
E-Mail Website
Guest Editor
Department of Horticultural Science, NC State University, Raleigh, NC 27697-7609, USA
Interests: Growing media; physical properties; plant-soil-water relationships
Dr. Jean-Charles Michel
E-Mail
Guest Editor
Research Unit EPHOR Physical Environment of Horticultural Plants, L’INSTITUT AGRO, EPHor, 2 rue Le Nôtre, 49045 Angers, France
Interests: growing media; soilless culture; physical properties; soil-water relationships; substrates wettability, water repellency and hydrology
Dr. Brian Eugene Jackson
E-Mail Website
Guest Editor
Department of Horticultural Science, NC State University, Raleigh, NC 27697-7609, USA
Interests: wood substrates; bark substrates; engineering raw materials; substrate particle dynamics; substrate hydrology; container plant root growth; substrate analytical methods

Special Issue Information

Dear Colleagues,

Advancements in soilless plant systems are occurring rapidly today. Innovations and new science make this one of the fastest-growing sectors in agriculture worldwide. The reasons for this are many: less arable land for food production; increased emphasis on locally produced crops; more traditional field-grown crops being produced in soilless systems; higher demand for more sustainable plant production practices; reduction of pollutants and emerging environmental and economic advantages to producing plants in containers. These advances in plant production practices have spurred the need for more research in these areas.

In addition, the concerns for increased food safety and local food security have accelerated the development and adoption of urban growing systems, container gardening, green roof systems, and vertical farming technologies, and other systems that utilize soilless substrates will continue to drive the demand for new and improved products with enhanced performance well into the future.

Once thought to be only relevant for greenhouse and nursery ornamental production, soilless substrates now are being used in consumable plant production including vegetables, herbs, leafy greens, soft fruit, and Cannabis. Creative thinking and proactive product development have yielded some remarkable advancements in plant production and thriving plant functioning systems. This issue is intended to highlight topics within these crucial scientific initiatives.

This Special Issue will focus on recent advances in the development, formulation, characterization, and utilization of traditional and novel soilless substrate materials (growing media other than mineral soils in situ) used in plant production systems and enclosed planting areas. We welcome high-quality novel research and reviews covering all related topics in soilless substrate science, including new and emerging components, substrate engineering and formulation, substrate characterization and analytical techniques, substrate hydrology and physical properties, water capture and management, chemical and phytotoxicological properties, reducing water and nutrient runoff, biological additives and microbial influences, advancement of technologies such as green roofs, vertical farms, and vertical gardening substrates, as well as other closely related research areas within soilless substrates.


Dr. William Carl Fonteno III
Dr. Jean-Charles Michel
Dr. Brian Eugene Jackson
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Agronomy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Novel organic and inorganic substrate materials
  • Substrate sustainability and climate change
  • Carbon footprint and life cycle analysis
  • Organic component processing and engineering
  • Availability and use of substrates in the future
  • Substrate analysis and characterization
  • Image analysis and tomographic technologies
  • Substrate particle dynamics
  • Substrate pH and chemistry
  • Substrate stability and biodegradation
  • Substrates for large containers and long-term crops
  • Substrate hydrological properties
  • Water use efficiency
  • Surfactant usage in substrates
  • Root growth and root architecture development in soilless container systems
  • Post-production shelf-life improvements in container crops
  • Propagation substrates
  • Soft fruit production in soilless systems
  • Cannabis production in soilless systems
  • Retail and consumer substrates
  • Additives and biostimulants for soilless substrates
  • Biological and microbial influences
  • Wood fiber production and utilization
  • Peat use and sustainability
  • Advances in compost utilization in substrates
  • Advances in biochar production and utilization in substrates
  • Urban gardens, green roof, and vertical farming systems

Published Papers (8 papers)

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Research

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Article
Substrate Stratification: Layering Unique Substrates within a Container Increases Resource Efficiency without Impacting Growth of Shrub Rose
Agronomy 2021, 11(8), 1454; https://doi.org/10.3390/agronomy11081454 - 22 Jul 2021
Viewed by 355
Abstract
Nurseries rely on soilless substrates to provide suitable growing media for container grown crops. These soilless substrates have been developed to readily drain water to prevent issues with waterlogging and associated soil-borne disease. A negative consequence of high porosity and subsequent drainage throughout [...] Read more.
Nurseries rely on soilless substrates to provide suitable growing media for container grown crops. These soilless substrates have been developed to readily drain water to prevent issues with waterlogging and associated soil-borne disease. A negative consequence of high porosity and subsequent drainage throughout the container profile is the required high or frequent irrigation rates with poor retention of applied nutrients. Substrates with relatively high levels of moisture and nutrient retention placed on top of a coarse and freely draining substrate could further optimize water and nutrient retention, while allowing for needed gas exchange for plant establishment and growth. Containerized Red Drift® rose (Rosa ‘Meigalpio’ PP17877) plants were grown under 16 mm or 12 mm daily irrigation, utilizing a traditional pine bark substrate or stratified substrates with either a conventional bark, bark fines, or a bark–peat mixture on top of a coarse bark within a container. The stratified substrates received 20% less controlled-release fertilizer; however, the fertilizer in the stratified treatments was concentrated in the upper strata only. During the first growing phase or season, plants grown in stratified substrates outperformed those grown in conventional, non-stratified bark substrates under normal irrigation. The stratified substrates did not reduce growth under reduced irrigation regimes. Overall, crop growth was equal or superior for stratified substrates when compared to the non-stratified controls, even with a 20% reduction of fertilizer. This research suggests that stratified substrate systems can be used to reduce fertilizer and irrigation rates while producing crops of similar or superior quality to conventionally grown containerized crops. Full article
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Article
Exploring Substrate Water Capture in Common Greenhouse Substrates through Preconditioning and Irrigation Pulsing Techniques
Agronomy 2021, 11(7), 1355; https://doi.org/10.3390/agronomy11071355 - 01 Jul 2021
Viewed by 701
Abstract
Particles in a substrate create a network of pore pathways for water to move through, with size and shape determining the efficacy of these channels. Reduced particle size diversity can lead to increased leachate, poor substrate hydration, and an inefficient irrigation practice. This [...] Read more.
Particles in a substrate create a network of pore pathways for water to move through, with size and shape determining the efficacy of these channels. Reduced particle size diversity can lead to increased leachate, poor substrate hydration, and an inefficient irrigation practice. This research examined the hydration characteristics of three greenhouse substrate components at three preconditioned initial moisture contents using subirrigation under five different irrigation durations and three water depths (2 mm, 20 mm, and 35 mm). Sphagnum peatmoss, coconut coir, and aged pine bark were tested at 67%, 50%, and 33% initial moisture (by weight). The objectives were to determine the impact of varying irrigation event durations (5, 10, 20, 30, 60 min) over a 60-min period, and the further influence of water depth and initial moisture, on the water capture abilities of peat, coir, and pine bark. The number of irrigation events depended on the irrigation event time of that experimental unit divided by the total time of 60 min, varying from 12, 6, 3, 2, and 1 event. Hydration efficiency was influenced by initial moisture content (IMC), water depth, pulsing duration, and inherent substrate characteristics (hydrophobicity/hydrophilicity). Initial MC had the largest impact on peat, regardless of water level or irrigation duration. Lower IMCs increased the hydrophobic response of peat, further reducing the amount of water the substrate was able to absorb. Pine bark had a 5–10% decrease in initial hydration between 67%, 50%, and 33% IMC, while coir’s hydrophilic nature reduced any IMC affects. At 50% IMC or less, coir had the highest volumetric water content (VWC) across all substrates, pulsing durations, and water depths. Water depth was found to increase initial hydration and final hydration 6–8% across all substrates. These three materials had altered and varied water capture responses depending on the combination of treatments employed. This work demonstrated the effects of intensity and exposure on substrates and the need for more integrated research for improving water use efficiency on container crops. Full article
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Article
Extrusion of Different Plants into Fibre for Peat Replacement in Growing Media: Adjustment of Parameters to Achieve Satisfactory Physical Fibre-Properties
Agronomy 2021, 11(6), 1185; https://doi.org/10.3390/agronomy11061185 - 10 Jun 2021
Viewed by 613
Abstract
Peat is a highly contentious input in agriculture. Replacing or reducing peat by substitution with lignocellulosic biomass processed into fibre by twin-screw-extrusion could contribute to more sustainable agriculture with regard to horticultural production. Therefore, plant wastes including pruning from Olea europaea L. and [...] Read more.
Peat is a highly contentious input in agriculture. Replacing or reducing peat by substitution with lignocellulosic biomass processed into fibre by twin-screw-extrusion could contribute to more sustainable agriculture with regard to horticultural production. Therefore, plant wastes including pruning from Olea europaea L. and Vitis spp. L., residues from perennial herbs like Salvia spp. L., Populus spp. L. and forest biomass were processed to fibre for peat replacement with a biomass extruder. The water-holding-capacity (WHC), particle-size-distribution and other physical fibre characteristics were determined and compared to peat. The specific energy demand during extrusion was measured for aperture settings from 6–40 mm. No fibre reached the 82% WHC of peat. At the setting of 20 mm of all materials investigated, Salvia performed best with a WHC of 53% and moderate specific energy demand (167 kWh tDM−1) followed by Olea europaea with a WHC of 43% and a low energy demand (93 kWh tDM−1). For Populus, opening the aperture from 20–40 mm decreased energy demand by 41% and WHC by 27%. The drying of biomass for storage and remoistening during extrusion increased the specific energy demand. Despite a lower WHC than peat, all investigated materials are suitable to replace peat in growing media regarding their physical properties. Full article
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Article
Effect of a Newly-Developed Nutrient Solution and Electrical Conductivity on Growth and Bioactive Compounds in Perilla frutescens var. crispa
Agronomy 2021, 11(5), 932; https://doi.org/10.3390/agronomy11050932 - 09 May 2021
Viewed by 621
Abstract
We evaluated the effect of a newly-developed nutrient solution of red perilla (NSP) with various electrical conductivity (EC) levels on plant growth, mineral content, and bioactive compounds. Four-week-old seedlings were grown in greenhouse nutrient solution as control (CT) (EC 1–3 dS m−1 [...] Read more.
We evaluated the effect of a newly-developed nutrient solution of red perilla (NSP) with various electrical conductivity (EC) levels on plant growth, mineral content, and bioactive compounds. Four-week-old seedlings were grown in greenhouse nutrient solution as control (CT) (EC 1–3 dS m−1) or NSP (EC 1–6 dS m−1). NSP 1 dS m−1 induced better growth characteristics, whereas higher EC levels inhibited plant growth. Most of the macro-elements contents significantly decreased under NSP 6 dS m−1, whereas the micro-elements contents fluctuated according to EC levels. Total phenolic concentration in NSP was lower than that in CT, and total phenolic content was highest under NSP 1 dS m−1. Total anthocyanin and antioxidant concentrations and contents increased at lower EC levels. Rosmarinic and caffeic acids concentrations increased at higher EC levels, whereas there were no significant differences in these compound contents among the EC levels. No difference in perillaldehyde concentration was observed, whereas the content was higher at lower EC levels. Overall, these results suggest that NSP 1 dS m−1 is suitable for cultivating red perilla in plant factories. Full article
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Article
The Use of Wood Fiber for Reducing Risks of Hydrophobicity in Peat-Based Substrates
Agronomy 2021, 11(5), 907; https://doi.org/10.3390/agronomy11050907 - 05 May 2021
Cited by 1 | Viewed by 437
Abstract
Peat substrates are well known to become hydrophobic during desiccation, thus degrading their water retention properties. Synthetic wetting agents are commonly incorporated to limit the risk of hydrophobicity, but substrates companies are searching for more sustainable alternatives. To that end, the effect of [...] Read more.
Peat substrates are well known to become hydrophobic during desiccation, thus degrading their water retention properties. Synthetic wetting agents are commonly incorporated to limit the risk of hydrophobicity, but substrates companies are searching for more sustainable alternatives. To that end, the effect of wood fiber addition in peat-based mixes was measured using contact angles and hydration curves. The study was carried out on two raw materials (white milled peat and wood fiber) and binary mixes. The results showed a shift from hydrophilic to more hydrophobic character with a decrease in the ability to rewet of peat-based substrates in relation to the intensity of drying, whereas wood fiber remained hydrophilic. Increasing wood fiber content in peat-based mixes improved the rehydration efficiency, but with a lower intensity of that measured with synthetic wetting agent addition. Our results highlighted the hydrophilic nature of wood fiber and demonstrated an additional benefit of wood fiber use in peat-based growing media. Full article
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Article
Biochar for Circular Horticulture: Feedstock Related Effects in Soilless Cultivation
Agronomy 2021, 11(4), 629; https://doi.org/10.3390/agronomy11040629 - 26 Mar 2021
Cited by 2 | Viewed by 793
Abstract
Biochar has previously been used in growing media blends as fertilizer or for improving plant growth, disease suppression, and as a sustainable replacement of peat. To achieve optimal circular horticulture, we propose here to reuse the biochar from spent growing media. However, it [...] Read more.
Biochar has previously been used in growing media blends as fertilizer or for improving plant growth, disease suppression, and as a sustainable replacement of peat. To achieve optimal circular horticulture, we propose here to reuse the biochar from spent growing media. However, it is unclear to what extent the biochar feedstock determines the mode of action of the biochar and if use of spent growing media biochar may encounter nutrient or salt problems. Differences in chemical characteristics, nutrient release, and interaction in a leaching experiment and effects on plant growth, nutrient uptake, and disease suppression in a strawberry greenhouse trial were studied for 11 biochars either processed from spent growing media or from lignocellulosic biomass. A well-studied biochar produced from oak wood was set as reference. Biochars produced from spent growing media were characterized by higher electrical conductivity, extractable and total nutrient concentrations compared with biochars produced from lignocellulosic biomass. Especially in the first phase of the leaching experiment, all biochars showed nutrient and salt release, with most prominent effects for spent growing media biochars and the reference biochar. The latter biochars were an important source of phosphorus and in particular of potassium. Only for the reference biochar, strawberry plants showed increased uptake of phosphorus, potassium and calcium, and increased chlorophyll concentration. No Bortrytis cinerea disease suppression and no increase in plant growth was observed for the tested biochars. It is concluded that spent growing media can be recycled as biochar in growing media without adverse effects compared to biochars produced from lignocellulosic biomass. Full article
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Article
Growing Medium Type Affects Organic Fertilizer Mineralization and CNPS Microbial Enzyme Activities
Agronomy 2020, 10(12), 1955; https://doi.org/10.3390/agronomy10121955 - 12 Dec 2020
Cited by 2 | Viewed by 887
Abstract
Managing plant fertilization is a major concern of greenhouse growers to achieve sustainable production with growing media (GM). Organic fertilization is popular but is more difficult to control, since organic compounds need first to be mineralized by microbes. After 7, 14, 28, and [...] Read more.
Managing plant fertilization is a major concern of greenhouse growers to achieve sustainable production with growing media (GM). Organic fertilization is popular but is more difficult to control, since organic compounds need first to be mineralized by microbes. After 7, 14, 28, and 56 days of incubation, we investigated the response of microbial activities and nutrient releases from three frequently used organic fertilizers (horn and two plant-based fertilizers) in three frequently employed GM types (peat, coir, and bark). We measured pH, electrical conductivity, nutrient contents (NH4+-N, NO3-N, PO43−-P, SO42−-S), and enzyme activities (β-1.4-glucosidase, urease, acid phosphatase, arylsulfatase). After fertilization, microbes in coir expressed all the C, N, P, and S functions studied, making related nutrients available. In peat and bark, some C, N, P, and S-related pathways were locked. Peat presented high NH4+-N and PO43−-P releases linked to high acid phosphatase and β-glucosidase activities, while bark showed high nitrification rates but weak enzyme activities. Fertilizer types modulated these responses with lower activities and nutrient releases with horn. Our results contributed to better understanding mineralization processes in GM, showing different microbial responses to fertilization. This study pointed out the necessity to look deeper into microbial functions in GM optimizing biological and physicochemical properties. Full article
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Review

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Review
Growing Mediums for Medical Cannabis Production in North America
Agronomy 2021, 11(7), 1366; https://doi.org/10.3390/agronomy11071366 - 05 Jul 2021
Viewed by 690
Abstract
The production and use of cannabis for medical purposes has been legalized in Canada and several states in the USA. Due to the historically illegal nature of cannabis, there is very little information available in academic publications about appropriate growing media for growing [...] Read more.
The production and use of cannabis for medical purposes has been legalized in Canada and several states in the USA. Due to the historically illegal nature of cannabis, there is very little information available in academic publications about appropriate growing media for growing cannabis. The purpose of this review is to provide an overview of the most commonly used growing media for the production of medical cannabis and to discuss their advantages and disadvantages. Based on current knowledge, there is a general agreement on the properties of a suitable growing medium within the cannabis industry. However, there is little consensus among growers on the best growing medium to grow cannabis. Different categories of growing media are widely used in North America. In this review, we classified them into several main categories principally based on the type of material used in their composition and the growth stages of the plant. The main categories include: coir-based, peat-based, rockwool, phenolic foam, and living soil. It is not easy to suggest the best growing medium for cannabis production. Each category of growing medium has its strengths and weaknesses. Overall, it seems that coir-based products are the intermediate substrates showing more advantages and less weakness; however, choosing any of these categories depends a lot on the growing technique and production system. Future research should focus on determining the optimal level of growing media properties to produce high yielding medical cannabis with the desired quality. Full article
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