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Review

Water Nutrient Management in Soilless Plant Cultivation versus Sustainability

by
Artur Mielcarek
,
Karolina Kłobukowska
*,
Joanna Rodziewicz
,
Wojciech Janczukowicz
and
Kamil Łukasz Bryszewski
Department of Environment Engineering, University of Warmia and Mazury in Olsztyn, Warszawska St. 117a, 10-719 Olsztyn, Poland
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(1), 152; https://doi.org/10.3390/su16010152
Submission received: 7 November 2023 / Revised: 15 December 2023 / Accepted: 17 December 2023 / Published: 22 December 2023
Browse Figures
Versions Notes

Abstract

:
Under-cover soilless cultivation is an important technique of crop production. Due to the lack of contact with soil and precipitation, the root system of crops grown must be provided with water and all necessary nutrients in the form of a solution (nutrient medium). This nutrient medium needs to be fed in excess to ensure proper plant development and the expected qualitative and quantitative parameters of the crop yield, which means that in the case of, e.g., tomato cultivation, 20–80% of the supplied medium must be removed from the root system and managed. Uncontrolled discharge of this drainage water poses a significant threat to the environment, causing contamination of surface waters and groundwaters. The article presents the latest solutions for drainage water management as well as technologies and systems that allow saving water and fertilizers, and thus recovering elements. It also characterizes methods deployed for the treatment of overflow that enable its recirculation, its re-use for fertilization of other less demanding crops (including soil crops), and its final management in the form of a discharge to the natural environment. Due to depleting resources of adequate-quality water, increase in the prices of mineral fertilizers, and depletion of natural phosphorus deposits, the future trends in water and nutrients management in this cropping system aim at closing circuits of drainage water and recovering elements before their discharge into the natural environment. These measures are expected not only to protect the natural environment but also to reduce the costs of crop production.

1. Introduction

According to Savvas et al. [1], soilless culture can be defined as “any method of growing plants without the use of soil as a rooting medium, in which the inorganic nutrients absorbed by the roots are supplied via the irrigation water”. Such cultivation entails use of a porous substrate—substrate culture soilless (SCS), or a nutrient solution without a solid phase—liquid-culture soilless (LCS) [2]. Soilless cropping systems have been practiced in ancient civilizations—the Egyptians used an unknown type of growing medium, probably much lighter than the soil, to transport trees from distant places to the royal palace [3,4]. The Aztecs, in turn, gave rise to the method of floating gardens based on hydroponics [3]. Currently, the greenhouse production of ornamental plants and vegetables is the largest industry branch based on the soilless cropping system [4]. The most commonly used neutral growing media are coconut fiber, mineral wool, pumice, and perlite [5]. In soilless growing systems, the plants receive essential nutrients through a nutrient-rich water solution, enabling more precise control over growing conditions. The main goal of soilless culture is to provide plants with optimal growing conditions, including nutrient levels, pH balance, and water availability [6,7].
Greenhouse crops require continuous and strict control [7]. Plant development, which is monitored on an everyday basis, is affected mainly by cultivation practices, the climate inside the greenhouse, conditions in the plant rhizosphere, and, finally, the protection of plants against diseases and pests. Nowadays, growing conditions are monitored by means of devices and systems that allow the producer to influence the controlled parameters. Although it seems unlikely, external conditions also largely determine greenhouse production [8]. They affect, among other things, the demand for heat energy in periods of low temperature in a moderate climate zone, or the electricity needed to illuminate plants under unfavorable sunlight conditions [9,10].
The global area of soilless cultivation is estimated to reach 95,000 ha [11]. In the European Union, more than 80% of the soilless cultures are located in five countries (the Netherlands, Spain, Poland, Italy, and France). The area of soilless cultivation in each of these countries exceeds 18,000 ha. In Poland, in 2022, about 5220 ha of vegetables were grown under covers, and their yield was estimated at 1.53 million tons. Tomatoes accounted for the major part of this yield, as they were grown on 1750 ha with the production rate estimated at 700,000 tons, which was 7% more than in 2021. For comparison, the yields recorded in 2004 and 2012 were 369,000 tons and 500,000, respectively [12].
The primary goal of greenhouse plant cultivation is to produce top-quality yields while maintaining economic balance and environmental neutrality. For this reason, solutions are being sought to minimize the volumes of water used for irrigation. This is achieved by boosting productivity, i.e., ensuring higher yield per drop of a solution used for fertigation and water re-use (recirculation) [13].
Unused surplus of nutrient medium in the form of drainage water (DW), also referred to as greenhouse wastewater, can be a source of valuable raw materials, including phosphates, nitrogen, calcium, potassium, and other micro- and macro-elements [14]. However, these compounds are very often irretrievably lost as a result of overflow discharge to the ground directly under the greenhouse or in its immediate vicinity, thereby contaminating groundwaters and surface waters. During cultivation of tomatoes on mineral wool, the amounts of nitrogen and phosphorus penetrating the environment may reach 23–245 kg N/ha and 2–54 kg P/ha per month, over a production period of 9–10 months [15,16]. This is especially important in the case of phosphorus because its non-renewable resources are estimated to deplete within the next 50–100 years, which makes the costs of its acquisition continuously increase [17]. At the same time, only five countries/regions in the world account for as much as 75% of the global export of phosphorus fertilizers, these being China, Russia, the European Union, Morocco, and the United States. Alarmingly, the disruption of supply chains as a result of a pandemic or the geopolitical situation in these countries poses a significant risk of price increases and of limited access to such fertilizers [18].
This review aims to provide an overview of water and nutrient management strategies in soilless plant cultivation, including overflow management, a description of technologies and systems enabling the saving of water and fertilizers, and methods for the treatment of drainage water generated in greenhouses. Further steps are proposed for the management of drainage water for sustainable cultivation under protected conditions.

2. Water and Nutrients Management

Due to the type of substrate, soilless cultivation systems may be divided into those where plant roots grow into porous mineral substrates (e.g., sand, mineral wool, gravel), organic substrates (e.g., peat, bark, rice husks) or a mixture thereof; and into hydroponic and aeroponic ones in which plant roots are immersed in a medium or in the air without permanent filling (Figure 1) [7].
Soilless tomato cultivation most often entails the use of substrates which, owing to their porosity, retain the nutrient medium, protect the roots from temperature fluctuations, and promote the flow of air and water [19]. These can be PE (polyethylene) or PVC (polyvinyl chloride) containers, plastic-lined planters, or plastic bags filled with mineral wool or coconut fiber that are placed in channels to collect a nutrient medium solution that is supplied by drip trays [1]. The width and length of the growing modules vary depending on the substrate used, the size of the containers, and the space available [20]. For example, modules with dimensions 1000 × 200/195 × 75 mm, 1200 × 200/195 × 75 mm and 1330 × 200/195 × 75 mm are frequently used in the greenhouse cultivation of tomatoes. Modules with these dimensions make it possible to provide an adequate volume of substrate for 4–6 plants. In the EU Member States, fruit vegetables are grown in the soilless system mainly on coconut fiber, pumice, perlite, and mineral wool, and are irrigated by means of a drip system. In turn, leafy vegetables and herbs are grown deploying a deep flow technique (DFT), nutrient film technique (NFT), and floating systems (Figure 1) [21].
In the deep flow technique, plants float on a floating platform and their roots are constantly immersed in a nutrient solution and aerated with diffusers [3]. This technique works well in the cultivation of plants that have a developed root system [19].
In the nutrient film technique (NFT), plants are grown in baskets suspended on a pipe or a PCV gutter at an angle of about 1–2%. The nutrient medium is delivered through channels and flows in accordance with the pipe’s fall (gravity) into a tank from which it is recirculated back and supplied continuously to the plants, keeping the root system at constant humidity [3,19]. The appropriate spacing of plants in the planter is determined depending on the crop type [19]. Plants producing little biomass, like lettuce, strawberries, and herbs, work best in this system. The medium composition changes slightly as it passes through the system, which enables its multiple recirculation before its composition changes so much that it will need to be exchanged [3].
There are also aeroponic systems, in which plants are supported, for example, in polystyrene panels, while their roots are suspended in the air. By this means, the roots are well aerated, which promotes faster growth of plants. The roots are periodically sprayed with a so-called nutrient mist to provide necessary nutrients and maintain adequate humidity. The frequency of nutrient medium spraying (usually every 2–3 min for 30–60 s) depends on the crop type, plant growth stage, the growing season, and sun exposure. Aeroponics is used for growing lettuce or spinach, and the yield produced can be up to 10 times higher than in the case of conventional soil cultivation [2,19,22].
Modern systems deployed in soilless crop cultivation provide fertilizers and water in an integrated way, and, therefore, the macroelements and microelements necessary for the proper growth of plants are delivered in the form of water-soluble fertilizer salts [6], whereas irrigation and fertilization are applied in a low-dose and frequent manner. Savvas et al. [1] distinguished the following irrigation systems: overhead, drip-irrigation, and subirrigation (Figure 1).
In overhead systems (above the plant), water or nutrients are delivered by irrigation pipes fixed over the plants on a platform that sprays the crops by sliding over them. These systems are commonly applied in the production of potted plants [1].
In drip-irrigation systems, water is delivered to the substrate or rhizosphere usually once an hour for a few minutes using drip emitters. Due to its precision and very efficient water use (this system ensures up to 95% performance [23]), it is the most commonly used solution, in particular for the cultivation of cucumbers, tomatoes, onions, or bell peppers, i.e., plants characterized by large biomass growth and requiring large volumes of water and nutrients [1,2]. In recirculated systems, excess medium is returned back to the tank and supplied at the appropriate frequency, while in the open system, it is supplied by slow dripping [19].
In turn, sub-irrigation is mainly applied to produce potted plants. The planters should be lined with a substrate having good capillary properties because the nutrient solution is applied below the rhizosphere and moves upwards due to capillary forces [1]. This also results in the concentration of salt in the upper layers, thus limiting the salinity of the nutrient solution, which runs slower than in the drop-irrigation system. In addition, the spread of pathogens that are not able to move in the opposite direction and do not reach the circulating solution is also reduced [21].
Regardless of the soilless cultivation method used, the nutrient medium flowing through the system undergoes a “concentration effect”. This is a negative outcome of the increase in nutrient concentration in the medium outflowing from the system, which results from the advantage of transpiration over the uptake of nutrients by plants. In order to maintain the appropriate values of the physicochemical indicators of the nutrient medium, an additional volume is used, which is referred to as overflow or drainage water (DW) [24,25].
Usually, such an overflow accounts for 20–30% of the nutrient medium delivered [15]. In the case of tomato cultivation, the standard volume of the overflow that can prevent nutrient medium salinization accounts for 25–50% [21]. However, when the electrolytic conductivity (EC) reaches 3–5 mS/cm or when evapotranspiration is diminished, the volume of DW can be from 20 to as much as 80% of the dosed nutrient medium [22]. Dyśko (2004) investigated the changes in nutrient content, pH and EC in the nutrient solution used for growing tomatoes on mineral wool and determined the increase in the change in concentration of the individual components. An increase in concentration occurred in N (62%), P (24%), K (48%), Ca (100%), Mg (91%), Na (112%), Cl (13%), S (75%), Fe (35%), Cu (100%), Zn (67%) and B (69%). There was also an increase in EC (54%) and pH (11%). In the studies cited, only Mn showed a decrease in concentration, which amounted to 15%. These values were calculated on the basis of average values from two years (2002–2003), which included 17 determinations per year made at weekly intervals. The cultivation was carried out in central Poland [24].
Open-circuit, closed-circuit, or cascade systems may also be distinguished considering the methods applied for the management of excess medium (Figure 2, Figure 3 and Figure 4) [7].

2.1. Open-Circuit Systems

In these systems, the excess DW is discharged untreated directly into the natural environment (Figure 2) [16]. This is commonly practiced in many places around the world, including Poland [21,26,27,28]. Open fertilization systems are widely found in almost all Mediterranean countries (e.g., Spain, Italy, Turkey, Morocco) [29,30] and in Portugal [31]. The procedure of frequent exchange of the nutrient medium in open-circuit systems facilitates its quality control and thereby enables achieving a crop yield of a desired quality and quantity. It also allows for easier protection of plants from infections [2]. Apart from being the most commonly used solution, this cultivation system also poses the greatest threat to the natural environment and is not viable economically considering the costs associated with water and nutrients consumption. At the same time, there is still a lack of technically and economically feasible large-scale solutions that could be implemented instead of open-circuit systems, which disrupt the environmental and economic sustainability of soilless crops. The scale of the problem is illustrated by the example of Spain, where only 12% of the 3000 hectares of soilless crops in Almeria are grown in a closed system. In South Korea, crops cultivated in a system with nutrient medium recirculation account for 5% of the 3355 arable hectares [32]. According to Dyśko et al. [33], the open-circuit system is still the main method for growing tomatoes in Poland, while recirculation is deployed only in a few facilities growing vegetables, including mainly those producing low biomass and requiring low variability of the nutrient medium composition [33].
DW outflowing from the soilless cultivation system has high concentrations of nitrogen and phosphorus, with the total nitrogen concentration ranging from 150 to 600 mg N/L, and that of total phosphorus from 30 to 400 mg P/L [34,35]. Mielcarek et al. [28] analyzed DW from a facility located in the north-eastern Poland, intended for tomato cultivation on mineral wool. The year-round qualitative analysis of DW demonstrated a concentration of nitrogen in the range of 270–615 mg N/L and that of phosphorus in the range of 35–104 P/L. In turn, in the study conducted by Kwon et al. [27], these values oscillated between 48–494 mg N/L and 12.7–106 mg P/L. Apart from nitrogen and phosphorus compounds, other macronutrients and micronutrients contained in the nutrient medium, such as calcium, magnesium, or potassium, are discharged with the drainage water [27,36]. Table 1 presents an overview of the physicochemical indicators of greenhouse effluents.
It is estimated that 170–335 kg N/ha, 34–95 kg P/ha, and 165–435 kg K/ha are lost during 9 months of tomato cultivation in the greenhouse at a water consumption of 400–500 L/m2 [21]. Breś (2009) presented the monthly nutrient losses with drainage water in open-circuit soilless cropping systems. They amounted to kg/ha*month in the case of tomato and cucumber cultivation for N 23-231, P 2-54, K 36-413, Ca 16-220, Mg 5-57, Na 4-62, Cl 1-34 and S 12-101 respectively. Lower losses were recorded for flower crops, which can be attributed to the lower concentration of ingredients in the nutrient solution. They amounted to kg/ha*month for N 10-83, P 1-16, K 13-106, Ca 9-54, Mg 3-21, Na 1-12, Cl 0.1-13, S 4-24. For Fe, Mn, Cu, Zn and B, the losses for tomatoes, cucumbers and flower cultivation did not exceed 1 kg/ha*month [16].
Malorgio et al. [40] determined that the annual water loss in the soilless cultivation of roses can be as high as 4282 m3/ha, thus resulting in up to 340–685 kg of nitrogen and 75–105 kg of phosphorus being discharged annually into the natural environment per crop hectare. Parada et al. [23] discharged 366.2 L/m2 of DW within 6 months of tomato cultivation on the perlite substrate using a 30% overflow. In a study by Muñoz et al. [26], the volume of DW discharged from tomato cultivation was 207.9 and 219.0 L/m2 at 28% and 39% overflow, respectively. In turn, Dyśko et al. [33] reported that 6-month tomato cultivation on mineral wool in the open-circuit system produced 3082 m3/ha of the overflow.
DW from open-circuit systems can theoretically be collected and re-used in recirculation systems or for fertilization of less demanding crops or field crops in a cascade system [20]. Massa et al. [41] determined differences in water losses in the soilless cultivation of tomatoes between open-circuit and closed-circuit systems. In a closed-circuit system, water losses reached 2680, 1960, and 1420 m3/ha over 167 days of cultivation with nutrient medium exchanged 14, 10, and 7 times, respectively, depending on the irrigation strategy. In contrast, 7168 m3/ha of drainage water was discharged during cultivation in the open-circuit system at the 50% overflow.

2.2. Closed-Circuit Systems

Closed-circuit systems are the future of soilless crop cultivation in greenhouses. In some countries, they are already legally mandatory, especially in nature-protected areas. They allow reducing water and nutrient losses caused by the use of the overflow. Unfortunately, their application faces serious challenges, like changes in the composition of the nutrient medium that has passed through the system, as well as the presence of pathogens and root secretions, including phytohormones, that inhibit plant development [6]. There are two main ways of managing the overflow in closed circuits: recirculation—using DW in the cultivation of the same crop (Figure 3), and the so-called cascade systems—using DW in the cultivation of another, less demanding crop (Figure 4) [42].
In some solutions (e.g., liquid-culture soilless) and crops with low biomass growth (e.g., herbs, bell peppers, strawberries, or seedlings), the recirculation of the nutrient medium does not require a significant development of the system. This is due to relatively small changes in the nutrient medium composition during the flow through the installation. In this case, the pH and EC measurements are usually sufficient to determine the fresh water dose needed to dilute DW in the next recirculation cycle, without the need to replenish the medium with nutrients. During cultivation of bell peppers on mineral wool in a recirculated system, the nutrient medium can be exchanged at a frequency of 4 to 8 weeks, whereas the EC and pH should be adjusted every 3 days. In strawberry cultivation, the nutrient substrate should be exchanged every 8 weeks, and in basil cultivation, every 2 weeks [43]. At the same time, these examples indicate that, despite the possibility of recirculation, DW should be discharged out of the system from time to time. However, the re-use of DW for a certain period of time may enable a 40–50% reduction in fertilizer consumption [44]. In the Netherlands and Belgium, soilless tomato cultivation with DW recirculation produces yields of between 80 and 90 kg/m2 and ensures 1 m3 water consumption per 70–160 kg of fruit. For comparison, in open-field conventional soil cultivation systems, the yield of tomatoes is 8–15 kg/m2 and 1 m3 of water is consumed per 6–15 kg of fruit [45]. However, in the case of growing tomatoes, which are characterized by high biomass growth, a high transpiration rate, and, above all, a growing period of one crop for up to 10–11 months within a year, DW recirculation requires much more advanced solutions. They are primarily aimed at protecting the crop from the spread of pathogens and the adverse effects of phytohormones and other root secretions. In this case, the recirculation system requires constructing stations for, i.e., disinfection or desalination of the nutrient medium or water used for dilution. Otherwise, DW recirculation can diminish the quantity and quality of crop yields that greenhouse owners cannot afford [42].
The electrolytic conductivity (EC) and pH are some of the most important parameters of the nutrient medium, as they affect the absorption of nutrients by plants, and their recommended values vary depending on the crop being grown [46]. The pH and EC measurements are fast, simple, and relatively cheap. The optimal pH for tomatoes is 5.5–6.0, and the EC should not exceed 1.9 mS/cm [47]. For comparison, the DW in soilless tomato cultivation is usually characterized by pH > 6.0 and EC > 3.0 mS/cm [28]. The pH value of the nutrient medium largely determines the uptake of individual elements. At pH > 7.0, the uptake of micronutrients (except for molybdenum) and phosphorus decreases, while macroelements, in particular sulfur, calcium, and potassium, are absorbed in excess. In turn, macroelements are not absorbed at pH < 5.0. The pH can be regulated in fertilizer tanks using nitric acid or phosphoric acid [46]. According to Tong et al. (2023), an increase in the electrolytic potential of 1 mS/cm beyond the optimum value may result in 10% losses of tomato yields [48]. Too low EC causes insufficient supply of certain nutrients to plants, whereas too high EC exposes them to soil salinity and physiological drought [6]. Achieving the desired nutrient medium composition requires knowing the DW composition and the right DW-to-water ratio. However, the concentrations of ions absorbed by crops depend on their species, the stage of crop development, and weather conditions. This means that determining the right doses is not an easy task. There are several methods of DW recirculation. The most commonly used solution involves mixing DW with fresh water and then, based on the EC of the final solution, supplementing nutrients mainly based on literature data and the experience of the technologist, rather than on current determinations of solution composition [21]. Another problem is posed by the accumulation of Na+ and Cl− in recirculated DW. They negatively affect the quantity and quality of the crop yield. For this reason, long-term recirculation of the same DW solution is impossible and the nutrient medium must be exchanged periodically [1]. Thus, even the most advanced closed-circuit systems generate greenhouse wastewater, which should be managed [20,21].
In any closed-circuit system, DW must be disinfected and treated before it can be re-used [44,49]. Sand filters or UV lamps are used to this end as measures preventing the spread of pathogens inducing, e.g., plant root diseases [1]. In addition to the above technologies, pasteurization via heat treatment or chemical treatment via ozonation or chlorination may also be deployed in the soilless substrate cultures [44]. Disinfection methods also include the addition of perhydrol, alone or coupled with UV radiation [50,51], as well as ultrafiltration and ultrasound [50].
The principle of operation of UV radiation with a wavelength of 254 nm is the flow of the disinfected liquid through quartz pipes equipped in mercury-fluorescent lamps. The radiation destroys the DNA of microorganisms by inhibiting the division of their cells. The power of the lamps (110–200 W), the radiation dose, and the UV-C light transmission, i.e., T10 transmission [51,52], are important to ensure process effectiveness. Typical T10 values are 10–20% for nutrient medium overflow through an organic substrate, 15–35% for mineral wool, up to 80% for closed systems, and 80–100% for rainwater. The transparency of liquids is diminished by, i.a., root secretions or iron chelates (the recommended dose of Fe chelates for tomato cultivation is 0.84 mg/L). Thus, the UV-C-based disinfection system should be equipped with sensors (UV, flow, pH, and T), an acid dispenser (nitric acid is most often used to reduce solution EC, cleaning quartz tubes, and DW disinfection), and possibly a perhydrol dispenser [51].
A fairly new, not yet fully proven, disinfection method involves the use of ultrasounds, which cause cavitation-based destruction of microorganisms. Very high frequency sounds result in the formation of ever larger and unstable gas bubbles between water particles, which at some point implode, destroying pathogens [50].
DW desalination and disinfection can also be performed via reversed osmosis, but this process entails high operating costs [34]. In this method, sedimentary and carbon filters are used in front of the ion-exchange membrane to remove suspended solids and organic molecules [53]. Martin-Gorriz et al. [54] applied reversed osmosis and ultrafiltration to treat DW in a hydroponic system. The re-use of DW allowed reducing the pressure of hydroponic cultivation on the surface waters of the receiver by 72%, but this resulted in a 37% increase in pressure on global warming and air acidification as a result of building additional infrastructure and equipment compared to the open-system cultivation.
Zamora-Izquierdo et al. [55] developed a highly automated crop management system that was tested in a greenhouse in tomato cultivation with recirculation. It consisted of four units: a nutrient medium preparation unit, an irrigation unit, a DW disinfection unit, and a tap water purification unit. In the nutrient medium preparation unit, nutrients, disinfected drainage water, tap water, and water from the reverse osmosis system were mixed, and the composition of the nutrient solution was automatically controlled based on EC, pH, and temperature using the fertilization control module. The irrigation control unit was installed in the irrigation unit, and the untreated DW was pre-filtered to remove contaminants. Disinfection was based on electrolysis, and the tap water purification unit was equipped with devices for reversed osmosis enabling reduction of the EC of the tap water used to dilute the DW. This system enabled over 30% savings in water consumption and over 80% savings in fertilizer consumption compared to an open-circuit system. Rufí-Salís et al. [56] tested an open and a closed system in the hydroponic cultivation of green beans on the roof. The DW was filtered using a sand filter, then disinfected with UV lamps. The study demonstrated 40% daily savings of water used for irrigation and 35–54% savings of nutrients in the case of the closed-circuit system (with recirculation). Fresh water may be sourced for recirculation from rainwater, but this requires constructing tanks for its retention. The annual amount of precipitation is also difficult to predict, especially in a changing climate [21]. In the Netherlands and Belgium, the vast majority of greenhouses are equipped with recirculation systems [57]. However, studies carried out in Dutch facilities for soilless crop cultivation have shown that, despite technical possibilities of recirculation, DW is discharged to the natural environment even at the slightest doubt as to the quality of water in terms of both its composition and the presence of pathogens or growth inhibitors [58].
There are also closed-circuit systems without recirculation, in which DW is accumulated in tanks and then used for the cultivation of other crops (cascade systems) [59].

2.3. Cascade Cropping Systems

Cascade systems involve the discharge of the nutrient medium from the primary crop, having high requirements regarding the medium composition to the secondary crop and exhibiting greater tolerance to changes in the nutrient medium composition (Figure 4) [60]. This cropping system is the least widespread [21]. The cascade management of the nutrient medium allows for savings in the consumption of water and minerals [29,60]. An example of the cascade management of DW was presented by Karatsivou et al. (2023) who used tomato as a primary crop, and then lettuce, spinach, and parsley as secondary crops [60]. The efficiency of nitrogen and phosphorus consumption increased by more than 50%, spinach yield increased by 14% compared to standard nutrient-medium-fed crops, whereas the efficiency of water consumption per lettuce, spinach, and parsley biomass growth was 50%, 30%, and 14% higher, respectively, compared to the standard nutrient medium. These results were due to the use of DW from the cultivation of a more-demanding crop with a nutrient medium having a much better composition compared to the standard medium that would be used in secondary crop cultivation. In turn, the results achieved by García-Caparrós et al. (2018) support the conclusion that crops intended for cascade cultivation should be appropriately selected [58]. The aforementioned authors irrigated rosemary crops with DW from the soilless cultivation of melon. In this case, the system enabled saving water and removing nitrates, but caused a decrease in rosemary yield compared to the cultivation variant with a standard nutrient medium. A key parameter for planning the number and type of plants that can be used in secondary cultivation is the variability of nutrient contents in the outflow from the primary cultivation [42]. A safe solution for cascade systems is to use DW from the soilless cultivation of field crops. Given the buffer properties of the soil, as well as a much larger area of open-field crops compared to under-cover crops, DW can account for a small percentage of the total fertilization used in this cropping system. However, the question of classifying DW as a fertilizing solution and placing it on the market remains unresolved.

2.4. Fertilizers

Proper and precise fertilization has a significant impact on the growth, development, and yield of plants. The composition of the nutrient medium is precisely calculated based on an analysis of water consumed for fertigation and adapted to the current stage of plant growth and atmospheric conditions, including primarily the temperature and the intensity of sunlight [61]. The fertilizing media are prepared from chemical compounds containing one or more nutrients. They also often contain non-nutritive compounds. Sixteen elements need to be provided to ensure the proper growth and development of plants, i.e., carbon (C), hydrogen (H), oxygen (O), phosphorus (P), potassium (K), nitrogen (N), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), and chlorine (Cl). An additional, but not necessary, element is silicon (Si). Phosphorus (which usually curbs the primary production in ecosystems) and nitrogen are of key significance considering natural environment protection, including mainly surface waters. The nutrient media should be prepared with high concentrations of components that are completely soluble in water. The basic fertilizers used for their preparation include: calcium nitrate, Ca(NO3)2; potassium nitrate, KNO3; magnesium nitrate, Mg(NO3)2; ammonium nitrate, NH4NO3; potassium sulphate, K2SO4; magnesium sulphate monohydrate, MgSO4∙H2O; magnesium sulphate heptahydrate, MgSO4∙7H2O; potassium monophosphate, KH2PO4; monoammonium phosphate, NH4H2PO4; calcium chloride, CaCl2∙6H2O; and potassium chloride, KCl. In addition, pH correction is achieved with nitric acid (V), HNO3, phosphoric acid (V), H3PO4, and hydrochloric acid, HCl, which serve as additional sources of nutrients. Iron, manganese, copper, zinc, boron, and molybdenum are introduced in the form of micronutrient fertilizers containing one, two, or more components. Apart from boron and molybdenum, these compounds are usually introduced in the form of chelates, ensuring good assimilation by plants. Fertilizer delivery devices include volumetric (quantitative) and proportional dispensers. The volumetric dispensers seem to be simpler to operate and are less expensive; however, they are dependent on changes in water pressure and do not adjust the fertilizer concentration to the fluctuations in pH or electrical conductivity (EC), unlike the proportional dispensers, which respond to these changes with the appropriate fertilizer dose [1].
In hydroponic cultivation, it is not possible to treat any macroelement or microelement as less important at any stage of plant growth due to the precision of fertilization. Each element plays an important role in physiological processes and in building the cells, tissues, and organs of plants. It is important to provide elements in a continuous manner because, in some cases, a deficiency or lack of a given element may result in serious disturbances in plant growth, deterioration of crop quality, or a significant reduction in crop yield. An example of this case may be the role of calcium, which determines, i.a., the rigidity of cell walls. It needs to be supplied continuously and in sufficient quantities, as the proper fruit nutrition from setting to harvest ensures plant protection against blossom end rot, which disqualifies the fruit from commercial use. Table 2 provides optimal ranges of nutrient contents for tomatoes grown in mineral substrates [62].
In recent times, the prices of minerals essential for fertigation have seen a notable surge, influenced by geopolitical factors and the ongoing pandemic. Analyzing the situation in Poland as of December 2022, it was observed that approximately 53% of the analyzed fertilizers, including nitrogen-based (such as ammonium nitrate, urea), phosphorus-based (like ammonium phosphate, superphosphate), potassium-based (potassium salt, potassium sulfate), and poly-compound fertilizers, experienced a more than 30% increase compared to the prices of the corresponding period in the previous year [63]. Looking ahead to 2023, there is a continuing upward trend in fertilizer prices, encompassing urea and ammonium nitrate, both in Poland and globally. In France, there has been a EUR 20 per ton increase in urea prices, whereas in the USA and the Middle East, urea prices have risen by almost USD 50 per ton [49].

3. The Impact of Soilless Cultivation on the Natural Environment

The environmental impact can be estimated based on the quantity and quality of the discharged DW described earlier. It is noteworthy that there are few studies showing the results of the determination of environmental quality within greenhouses. The use of closed-circuit systems in soilless crop cultivation is more environmentally friendly, but unfortunately is not as widespread as the use of open-circuit systems [19]. However, both systems generate DW which needs to be discharged into the natural environment. Uncontrolled discharge of untreated DW causes all the nutrients present in the medium (in particular nitrogen, potassium, calcium, and magnesium) to pervade the environment [25]. These pollutants have the ability to migrate in the ground, which causes contamination of groundwater, wells, and rivers located even at a considerable distance from the contamination source, i.e., the greenhouse [64]. In the case of surface waters, an additional dose of biogenic compounds, especially phosphorus, significantly accelerates their eutrophication [45,56]. This is an undesirable and dangerous phenomenon having multiple consequences, including the mass blooming of algae, a deficit of dissolved oxygen, and the release of toxins [53]. Investigations conducted by Komosa and Roszyk [65] and Kowalczyk et al. [66] indicate that the concentration of certain minerals in well waters increased in the vicinity of greenhouses with crops grown in the soilless system with open water and sewage management systems. Similar observations were made by Komosa [67], who investigated the mineral composition of water from wells located in the vicinity of Kalisz city (Poland). His research demonstrated an increase in the pollution of well waters with plant nutrients and ballast ions. Dyśko and Kaniszewski [68] studied samples of groundwater collected from under the greenhouse and from the area located 25 m and 300 m away from the greenhouse. The nitrate nitrogen content (N–NO3) was 117 mg/L and decreased proportionally to the distance from the greenhouse. Furthermore, Kowalczyk et al. (2013) [69] analyzed water from deep-water wells located in areas with a high proportion of soilless crops between 2011 and 2013. It turned out that not only groundwater, but also deeper water layers were affected by greenhouse-derived contaminants as they contained both nutrients and ballast components and had slightly alkaline pH (pH = 7.00–7.07) and EC > 0.7 mS/cm. In the case of water with such a high EC, it is difficult to determine the correct proportions of components of the nutrient medium, which often prevents its use in soilless crops, especially in the case of such species as greenhouse cucumber. Vegetable production also entails the use of plant protection agents that can penetrate the natural environment [45]. Pesticides are intentionally used to protect crops from fungi, insects, or weeds, but when they pervade the natural environment they pose a threat to various aquatic organisms, fish, soil microorganisms, birds, and even humans [70]. Vermeulen et al. [71] conducted a study which demonstrated that up to 3.3% of the plant protection agents used in greenhouse cultivation were emitted into the environment. The scale of these point sources of contamination means that the greenhouse may be considered a real threat to the natural environment.
The use of different substrates can also have an adverse impact on the natural environment. Drainage water from tomato cultivation on organic substrates has been found to contain less nutrients than that from cultivation on mineral wool, and, therefore, the organic medium has been found to be more beneficial for the environment [68]. On the other hand, the extraction of peat (organic substrate) from peat bogs, which constitute wildlife habitats and are very important for the hydrological cycle and water quality, can upset the environmental balance. Hence, substitutes are being sought for this type of substrate; sand and bark seem competitive in this case as they have a small carbon footprint and are relatively cheap. Life-cycle assessment is a useful method for determining the various environmental impacts associated with a product throughout its life span [23]; therefore, attention is paid to problems posed by the disposal of substrates and high energy consumption during production, as in the case of using mineral wool [7].
Various strategies for managing the overflow can be implemented, including closed-circuit or cascade systems, to mitigate the effects of wastewater discharge from the greenhouse [64]. The re-use of the nutrient medium can minimize, for example, the effects of eutrophication of water receivers; however, it should be borne in mind that a closed-circuit system requires additional infrastructure needing electricity supply, thus contributing to global warming and the scarcity of fossil resources to a greater extent than an open (linear) system does [54,56].

4. Methods for the Final Management of the Overflow

Depending on whether the nutrient medium is returned to the system or discharged outside the greenhouse, various techniques are deployed for its treatment. In a closed-circuit system with recirculation, these are methods allowing its disinfection (removal of pathogens and root secretions) and desalination (Section 2.2).
During DW discharge into the environment, attention is focused primarily on reducing the concentrations of nitrogen and phosphorus, i.e., the elements that have the greatest impact on the eutrophication of water reservoirs [34]. It is also important to remove the remaining contaminants contributing to salinity increase, which is, however, often performed during DW denitrification and dephosphatation [53]. The low content of organic compounds impairs the application of conventional treatment methods based on activated sludge or biofilm; therefore, search is underway for technologies that would enable overflow pre-treatment or treatment [53]. Well-known solutions that work well with other types of wastewater and lesser-known ones based on the specific qualitative composition of DW have been tested in this respect.

4.1. Nature-Based Solution

One of the most popular full-scale solutions intended for final DW management is constructed wetlands (CW). Here, treatment is aided by heterotrophic microorganisms as well as water and hydrophilous plants, which incorporate nitrogen and phosphorus into their biomass. Most often, CWs are planted with cane (Phragmites australis), common rush (Scripus lacustris), or willow (Salix viminalis). The advantages of CWs include their natural appearance, easy and simple operation, competitive operation costs, and the fact that they do not generate secondary sewage sludge [34,72]. In addition, biomass collected from CWs can be used as an organic fertilizer, animal feedstuff, or energy substrate, e.g., in methane fermentation [73]. CWs represent a buffer between the greenhouse and the natural environment. They promote intensification of natural processes in the environment that has received this type of wastewater, in a specific space enabling monitoring. In the case of soilless cultivation facilities, the challenge is to find the right space with the right soil and water conditions to build CW, which would ensure high treatment efficiency with long-term DW discharge practically all year round. This is due to the fact that the operation of such systems in the winter yields a low removal efficiency of nitrogen (about 4%) and phosphorus (about 6%). The addition of an external carbon source is then helpful, as it improves N and P treatment efficiency to 79% and 30%, respectively [74]. However, given the contaminant load of DW, this extent of treatment poses a threat to the natural environment. The efficiency of CW action can be increased by applying various wastewater distribution systems, including, for example, horizontal subsurface flow, vertical subsurface flow, surface flow, and multi-stage combined flow systems [72].
Park et al. [75] used a hybrid CW with subsurface horizontal flow for the treatment of hydroponic wastewater. They attempted to combine autotrophic and heterotrophic processes based on sulfur (thiosulphate and elemental sulfur), which allowed them to achieve 71.5% and 65.3% removal efficiency of thiosulphate-based and elemental-sulfur-based nitrate nitrogen, respectively. In turn, using heterotrophic denitrification alone, they achieved ca. 43% removal efficiency of N-NO3.
In turn, Putri and Hung [37] used duck weed (Lemna minor) to treat synthetic wastewater with a composition similar to that from soilless citrus cultivation and achieved 23% and 40% removal efficiency of total N and P, respectively.
Apart from biogenic compounds, chlorine and sodium ions accumulate in the recirculated medium, which are harmful to crops in excess amounts. Rozema et al. [76] used four plant species (Typha latifolia, Schoenoplectus tabernaemontani, Juncus torreyi, Typha angustifolia) to remove Na+ and Cl−. These plants are able to survive excessive salinity and maintain an appropriate osmotic gradient by accumulating and storing salt ions in their vacuoles. The study results showed that T. latifolia enabled the removal of 12% of Na+ ions and 23.4% of Cl− ions, whereas S. abberaemontani enabled the removal of 8.7% of Na+ and 26% of Cl− ions.
Another solution based primarily on natural processes is that of microalgae culture. Microalgae are microorganisms that, like hydrophyte plants, use organic compounds, nitrogen, and phosphorus contained in wastewater for growth [77]. Growing algae in nutrient media from soilless cultures is considered a promising technology in the treatment of greenhouse wastewater and, at the same time, allows for its alternative application [34]. This solution refers to the cascade circulation of the nutrient medium, where microalgae are less demanding. They remove contaminants to very low concentrations [77], and at the same time, use CO2 for photosynthesis, thereby contributing to reduction in greenhouse gas emissions [78]. Algal species, such as Chlorella vulgaris and Dunaliella salina, achieve biogenic compound removal efficiencies of 70.2% N and 98% P [79], as well as 80% N and 97% P [34]. Saxena and Bassi [35] reported equally high removal rates (95.2% N and 93.6% P) using Dunaliella salina. In turn, Aravinthan et al. [78] removed biogenic compounds from wastewater generated during soilless cultivation of ice lettuce with Chlorella vulgaris and achieved ca. 27.9% and ca. 22.7% removal efficiency of N and P, respectively. They also confirmed that this algal species uses ammonia from wastewater in the first place. Different conclusions were reached by Baglieri et al. [79] who analyzed Chlorella vulgaris and Scenedesmus quadricauda (grown in a medium derived from the cultivation of cherry tomatoes), because according to their study results, these algae species showed a preference for nitrates rather than for ammonia nitrogen. However, this may have been due to a too low N-NH4 concentration in the culture medium. The above-cited authors achieved a nitrate removal efficiency of approximately 99% for both algae species and phosphorus removal efficiencies of 94% and 89% for C. vulgaris and S. quadricauda, respectively.
Particular attention is owed to aquaponics, which is a sustainable microecosystem that couples aquaculture and hydroponics, exploiting the symbiosis of flora and fauna, i.e., wastewater from the aquaculture subsystem is re-used for growing plants in the hydroponic subsystem. Fish feces satisfy the nutritional needs of plants, and water from the fish tank may be recycled owing to microbiological nitrification and denitrification [80,81]. Based on their study results, Yang et al. [82] concluded that aquaponic systems are more efficient and generate fewer N and P losses (59–70%, 38–54%) than hydroponic systems (76–87%, 79-89%). When selecting fish species for aquaponics, various criteria must be taken into account to ensure the success and sustainability of the system. Some of the most important criteria for the selection of fish species in aquaponics are temperature and tolerance to a wide range of physico-chemical water parameters [80]. Criteria such as growth rate, feeding habits, size and space requirements, reproduction and life cycle, and disease resistance are also often considered [81]. The most commonly cultivated species of fish include tilapia, koi, carp, and catfish, whereas the most often grown plants include lettuce, kale, basil, tomatoes, bell peppers, and cucumbers [83]. Nitrogen metabolism can be determined depending on the plant species used. A study conducted by Hu et al. [84] in an aquaponic system for tilapia culture compared the nitrogen consumption efficiency in the cultivation of tomato and pak choi, which reached 41.3% and 34.4%, respectively. In addition, the tomato-based aquaponics system was characterized by better water quality. In turn, Wongkiew et al. [85] used lettuce, pak choi, tomatoes, and chives in combination with tilapia culture. The highest nitrogen recovery was achieved during tomato cultivation of 44.0% and the lowest one during chives cultivation of 1.7%.

4.2. Physicochemical and Biological Methods for the Final Management of DW

Physicochemical and biological methods have been deployed for the final management of DW relatively late. The denitrification method involves reducing nitrates and nitrites to molecular nitrogen and is based on metabolic processes carried out by facultative anaerobes. Depending on the electron donors they use, denitrification may be divided into heterotrophic (a donor from organic sources, e.g., acetic acid, methanol, sodium acetate [86]) and autotrophic (a donor from inorganic sources, e.g., carbon dioxide, bicarbonates) [87]. In the search for new, cheaper carbon sources, some researchers have focused their attention on plant waste. For instance, Park et al. [88] used leachate from pre-treated plant waste and achieved 85% and 90.5% efficiency of nitrates and phosphates removal from hydroponic wastewater containing over 300 mg N/L. In turn, Castellar et al. [89] saw potential in cork pellets that could aid denitrification-based treatment of hydroponic wastewater; however, this potential has not been studied on a larger scale, and the cork itself may also be a source of phenolic compounds, which limits its applicability as a filtration medium.
Kwon et al. [27] achieved high treatment efficiency of DW from hydroponic culture by its denitrification in a sequencing batch reactor (SBR) with methanol as a carbon source. The removal rate of phosphates was 99.8% and that of nitrates was 89.5%. The removal efficiency was also determined for calcium (48.3%), potassium (17.5%), magnesium (14.1%), sodium (15.2%), and dissolved iron (67%). In turn, Bryszewski et al. [90] used a sequential batch biofilm reactor (SBBR) for the treatment of wastewater from soilless tomato cultivation. The application of sodium acetate produced a significant increase in the efficiency of contaminants removal (81% of nitrogen; 91% of phosphorus).
The research group of Rodziewicz et al. [91] coupled biological and electrochemical processes and applied simultaneous removal of nitrogen and phosphorus via auto- and heterotrophic denitrification as well as electrochemical nitrate reduction and phosphorus electrocoagulation in a rotating bioelectrochemical contactor. The 24-h hydraulic retention time enabled achieving 68% and 99% nitrogen and phosphorus removal efficiency using a direct electric current. In addition, a study conducted by Bryszewski et al. [38] demonstrated that hydrogenotrophic and electrochemical processes can also be assisted by alternating electric current. In turn, a study by Mielcarek et al. [39] showed that the use of alternating current was viable in increasing the rate and effectiveness of denitrification, but only when electric current was applied simultaneously with an external source of organic carbon.
Equally interesting seem to be the methods for phosphorus recovery from wastewater via precipitation. For example, phosphorus was removed from hydroponic wastewater (at a removal rate of 97.8%) by its alkalization (pH increased to 7.5), and then nitrate nitrogen was removed with 95.2% efficiency during Dunaliella salina algae culture [35]. One of the first attempts to recover phosphorus from artificial greenhouse wastewater was carried out by Dunets and Zheng (2014). They used artificial wastewater solutions containing four PO4–P concentrations: 20, 50, 90, and 190 mg P/L, chosen to represent the common P concentration range in greenhouse wastewater, as reported in the literature [92]. In order to precipitate phosphorus, these authors used hydrated lime, obtaining 99% efficiency with a lime to P ratio (molar ratio of CaMg(OH)4: PO4–P) of 1.5. Optimal P removal was reported when lime addition increased the pH from 8.6 to 9.0 [88]. Alkalization was also applied by Mielcarek et al. [93] who demonstrated that the removal efficiency of phosphorus from greenhouse wastewater increased with pH increase and approximated 99% at pH 9. At the same time, calcium, magnesium, sulfur, manganese, and boron were removed from DW. Sorption processes can also be used to remove both nitrates and phosphates. Jóźwiak et al. [94] used the sorbents, non-crosslinked chitosan (53% nitrate removal efficiency and 93% orthophosphate removal efficiency) and epichlorohydrin-crosslinked chitosan (75% and 77% removal efficiency of nitrates and orthophosphates, respectively), in the form of hydrogel beads.

5. Conclusions

Appropriate water and wastewater management in soilless cropping systems allows maintaining economic balance and environmental neutrality. It is important to turn to closed-circuit systems that can enable nutrient medium recirculation, thereby contributing substantially to saving water and fertilizers. There are more and more new technologies that enable precise preparation of the nutrient medium (with the appropriate EC and pH values), using drainage water, which after disinfection can be re-used for the cultivation of the same or another crop. Closed-circuit systems require additional infrastructure, which entails higher costs. Perhaps for this reason, many investors remain with open-circuit systems, in which excess of the nutrient medium is usually discharged into the soil under the greenhouse. At the same time, the excess of the medium must be discharged outside the facility after a certain number of cycles even in closed-circuit systems. This wastewater has high concentrations of nitrogen and phosphorus. When it penetrates into the aquifers in the ground, it causes multiple adverse effects resulting in groundwater pollution and eutrophication of water bodies. For this reason, newer solutions are being sought to effectively manage the outflow from the facilities for soilless plant cultivation in greenhouses. In addition to the relatively popular nature-based solutions, increasing attention is devoted to research on physicochemical and biological processes taking place in separate reactors, which besides removing contaminants, also allow for the recovery of valuable elements. In light of climate change and the increase in the world’s population with the associated demand for food, the recovery of water and nutrients for crop production is crucial. Given the concerns of protected crop growers about potential damage to crops from improperly managed recirculation, a reasonable solution appears to be the recovery of nutrients from drainage water and the discharge of treated effluent into the environment. Based on the analysis of literature data and our own data, it is now possible to recover almost 100% of the phosphorus from the drainage water and to a large extent also calcium, magnesium, manganese, and boron. A high level of denitrification efficiency is achieved. This allows drainage water to be safely discharged into the environment where it can contribute to surface and groundwater resources. The recovered nutrients can be reused in fertigation or other crops. Further research should aim to optimize the recovery of nutrients from drainage water and their reuse.

Author Contributions

Conceptualization, A.M.; software, K.K.; literature review, A.M., K.K. and K.Ł.B.; formal analysis, W.J. and J.R.; writing—original draft preparation, A.M. and K.K.; writing—review and editing, A.M. and K.K.; visualization, K.K. and A.M.; supervision, W.J. and J.R.; project administration, A.M.; funding acquisition, A.M. All authors have read and agreed to the published version of the manuscript.

Funding

The study was part of the project “Development of a precise treatment of wastewater from soilless tomato cultivation technology using electro biological hybrid reactor” as part of the LIDER X programme, financed by The National Centre for Research and Development No. LIDER/4/0019/L-10/18/NCBR/2019. Co-financing amount: PLN 1,492,500.00.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Sustainability 16 00152 g001
Figure 1. Fertigation methods.
Figure 1. Fertigation methods.
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Figure 2. Open-circuit systems.
Figure 2. Open-circuit systems.
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Figure 3. Closed-circuit systems—recirculation.
Figure 3. Closed-circuit systems—recirculation.
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Figure 4. Closed-circuit systems—cascade systems.
Figure 4. Closed-circuit systems—cascade systems.
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Table 1. Concentration of pollutants in greenhouse wastewater discharged from soilless crops.
Table 1. Concentration of pollutants in greenhouse wastewater discharged from soilless crops.
ParametersTomato
[36]		Tomato
[24]		Citrus Nursery
[37]		Tomato
[38]		Hydroponic
Vegetable Greenhouse
[35]		Tomato
[27]		Tomato
[39]		Tomato
[28]
pH- 5.35 6.226.45.405.56.5 5.43 --
EC mS/cm 7.57 4.603.66.09-3.0 6.15 4.4–6.94.9–6.9
Total nitrogenmg/L 592.3 439514.5501.8466242 504.7 403.6–614.8270.0–577.4
Total phosphorus 145.9 76161.781370106 79.3 35.4–78.054.1–104.0
Ca 797.0 4029.28588.8539334---
Mg 181.1 1212.33261.6-140---
S-SO4 475.0 194.351.1 -61---
K 1276.9 522- -163---
Cl 91.8 17- -- --
Fe 0.127 3.511.490.5920.22- 0.492 --
Cu 0.13 0.380.52 0.03----
Zn 1.65 2.601.16 0.76----
Mn 0.738 0.610.90 0.03----
B 1.75 0.68- 0.01----
Al <0.02 --0.017-- 0.016 --
Mo 2.87 -- -----
Table 2. Optimal range of nutrient contents in soilless tomato cultivation.
Table 2. Optimal range of nutrient contents in soilless tomato cultivation.
ParametersConcentration [mg/L]
N-NO3220–230
P30–60
K360
Mg50–80
Ca200–210
SO480–100
Fe1.2–1.6
Mn0.5–0.1
B0.3–0.5
Zn0.3–0.35
Cu0.12
Mo0.05–0.1
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Mielcarek, A.; Kłobukowska, K.; Rodziewicz, J.; Janczukowicz, W.; Bryszewski, K.Ł. Water Nutrient Management in Soilless Plant Cultivation versus Sustainability. Sustainability 2024, 16, 152. https://doi.org/10.3390/su16010152

AMA Style

Mielcarek A, Kłobukowska K, Rodziewicz J, Janczukowicz W, Bryszewski KŁ. Water Nutrient Management in Soilless Plant Cultivation versus Sustainability. Sustainability. 2024; 16(1):152. https://doi.org/10.3390/su16010152

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Mielcarek, Artur, Karolina Kłobukowska, Joanna Rodziewicz, Wojciech Janczukowicz, and Kamil Łukasz Bryszewski. 2024. "Water Nutrient Management in Soilless Plant Cultivation versus Sustainability" Sustainability 16, no. 1: 152. https://doi.org/10.3390/su16010152

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