2022 Volume 10 Pages 101-114
Agriculture has been the most common way of food resources for centuries, and it is also closely linked to food security, rural development, and poverty reduction. Traditionally, the soil has been thought to be the most important prerequisite for growing food crops, but hydroponics techniques are currently considered one of the most popular plant-growing systems around the world. Plants are grown in a soil-free environment with the appropriate fertilizer solution, exactly required water, and no pesticides. Hydroponics is classified into distinct systems based on the principles of operation. Hydroponics has been utilized as a standard method for many aspects of plant biology research employing various systems, automation, and operation control methods. Aside from promoting healthy plant growth, using hydroponics there are other various advantages, including year-round production, enhanced yields, quality, and environmental benefits. Much research has been conducted utilizing hydroponics to investigate plant responses to biotic and abiotic stressors. This agriculture system will aid in the advancement of technology as a mission for future generations to become a self-sustaining model, as it is a promising way in the face of a global food security crisis.
Hydroponics is a technology wherein plants are grown in a soil-less environment with required nutrient solutions, less water, and zero pesticides. There is ‘No Role of the Soil’ in a hydroponic system. The nutrient solutions containing crop-specific nutrient components in the right concentration with balanced pH and EC are delivered to the roots in a highly soluble format and a controlled environment [1]. A hydroponics system generally comprises of few essentials like a growing tray, a reservoir, a timer, a controlled submersible pump, a delivery system, an air pump, an air stone to oxygenate the nutrient solution and grow lights (either natural or artificial) at a required range. Plants can be grown via hydroponics using various technologies like drip irrigation systems, automatic temperature control using evaporative cooling and light controlling systems, etc. replicating a complete artificial farming area, isolated from the outside environment, which also includes greenhouse farming, mainly for protecting the plants from extreme weather conditions during winter as well as summer [2]. The plant production factories use a series of plant growth facilities through artificial regulation of the indoor environment, such as lighting, temperature, CO2, and nutrient solutions, to achieve higher yields of plants [3, 4, 5].
In food production, hydroponics has many advantages as the composition of hydroponics solution can easily modify, so physicochemical phenomena and altering the efficiency of the nutrient acquisition process by a series of nutrient interactions in the plants. That’s led to the improvement of plant production from both qualitative and quantitative points of view. This cultivation offers a huge potential approach that is indisputable and ranges of advantages to environmental benefits because of its higher efficiency in using nutritional and water resources [6, 7].
It is a controlled system; the outcomes are highly predictable and can be well defined. The unpredictability in the traditional farming system can be reduced to a great extent by hydroponics. This emphasizes the urgent need to look at this system not only as adjunct technology or parallel technology for farming, but also as a mainstream strategy for Indian farming. This demands a comprehensive review encompassing not only science and technology aspects but the market need, quality aspects and challenges of abiotic and biotic factors. With this aim, we have structured this review, which we envisage to be a ready reference for all professionals in agriculture and agro-biotechnologists.
Hydroponics is not a new technology as considered by few. There are records in history where it has been practiced to grow plants without soil for centuries. The hanging gardens of Babylon, known as floating gardens of Mexico, and those of the Chinese floating gardens were grown using hydroponics. Soilless farming has also been referred to in Egyptian hieroglyphic records dating back several hundred years B. C. It was recorded that there were various experiments in crop nutrition done by Theophrastus (372–287 B.C.). In 1666, Irish scientist Robert Boyle explained growing plants with their roots submerged in water [8]. In 1699, another attempt at growing plants in a soilless environment was made by John Woodward, an English scientist who performed experiments on spearmint [9]. The basic concepts of growing plants using hydroponics were established in the 1800s by those investigating how plants grow [10]. Hydroponics was further popularized in the 1930s in a series of publications by a California scientist Dr. Gericke, who developed a laboratory technique on a commercial scale [11]. Allen Cooper of England established the Nutrient Film Technique (NFT) during the 1960s [10]. During the 1960s and 70s, marketable hydroponics farms were established in Abu Dhabi, Arizona, Belgium, California, Denmark, Germany, Japan, Holland, Iran, Italy, Russian Federation, and other countries [12]. Around 1970, the energy-saving poly greenhouse covers, PVC pipes used in the feed systems, and injector pumps and reservoir tanks were made of types of plastic [13]. By 1995, over 60,000 acres of hydroponics greenhouse vegetables were being grown, across the world, an acreage that is expected to increase further [9]. In 2004, Hydroponics Merchants Association published a report regarding ~55,000 acres of hydroponics greenhouse vegetable production worldwide. This included about 1,000 acres in the United States, 2,100 acres in Canada, and 2,700 acres in Mexico [10]. In the space program, this cultivation is being adopted to supplement a healthy diet, eliminate toxic carbon dioxide from the air inside Spacelab and create life-sustaining oxygen. Moreover, NASA has done extensive research on hydroponics for its Controlled Ecological Life Support System (CELSS). Nowadays, companies worldwide are vigorously working on and establishing hydroponics. Historical aspects of the techniques are shown in Figure 1.
Figure 1: Historical aspects of the techniques
Both active and passive hydroponics systems can be categorized based on some factors as shown in Figure 2. Currently, many hydroponics techniques are used for growing plants, which are classified into three categories based on the system's function. The first category is based on the system design, including wick, drip, water, nutrient film technique, ebb-flow nutrient solution, and aeroponics system. The second category is based on the aspect of hydroponics and how the nutrient solution in the system functions. Systems involved in the second category are closed and open systems. The third category is based on growing media used, including aggregate and liquid hydroponics systems. The hydroponics systems are designed based on specific requirements of plants with the most reliable and efficient methods of nutrient supply. The three primary conditions are (a) Proper quantity of nutrient solution to the roots while avoiding stagnation, (b) aeration to the root zone should be maintained to supply oxygen and remove CO2, (c) dehydration of roots should be prevented by maintaining relative humidity.
Figure 2: Classification of hydroponics systems
In hydroponics, substrates play a crucial role as many failed plant growths are related to roots becoming too wet or too dry, not sustainable, too expensive, and releasing toxic substances. As much as plant growth depends on the type of hydroponics system, it equally depends on the substrate used in hydroponics. Depending on the materials used in substrate, plants can stimulate homogeneous exploration by roots to attain a well-distributed and abundant root system at different levels. Materials used as substrates in hydroponics systems and their characteristics are given in Table 1. Substrates used in hydroponics are divided into two types such as fibrous and granular substrates [14, 15]. Fibrous substrates can be organic or inorganic. They are characterized by the presence of different fibre sizes or their modest air capacity or free porosity, and high water-retention capacity [16]. Granular types of substrates are generally inorganic. They are characterized by different particle sizes, textures, high porosity, and free draining. These types of substrates had poor water-holding capacity and retained water in a substrate, which is not easily accessible to the plant. So, the substrate volume required per plant is more than a fibrous substrate [17].
| Substrate | Characteristics | Example |
|---|---|---|
| Organic | This group includes natural organic substrates, their residues, by-products, and waste of organic nature derived from agricultural or from industrial by-products obtained from the wood industry. These constituents can be further subjected to processing, such as maturation and extraction. | Peat, Coconut fibre |
| Inorganic | This group includes natural materials as well as mineral products obtained from industrial processes. | Sand, pumice, vermiculite, perlite, expanded clay, stone wool, zeolites |
| Synthetic | This category includes both ion-exchange synthetic resins and low-density plastic materials. The materials obtained from this type are known as “expanded”. As they are produced by a dilation process at higher temperatures. They are not used widely, even though their physical properties are suitable to the other substrate's characteristics. | Expanded polystyrene, polyurethane foam |
Hydroponics aided plant researchers in identifying which elements were essential to plants, in what ionic forms, and what the optimal concentrations of these elements were. It allowed us to understand the effects of elemental deficiencies and toxicities and to study other aspects of plant development under more controlled conditions [18]. Although 60 elements are found in various crops, only 16 elements are generally considered to be essential for a physiological role in crop growth. These fundamental elements are classified as significant nutrients (C, H, and O), these are the basic necessity of crops; the macronutrients (N, P, and K) required by plants in relatively large quantities, the micronutrients (Ca, S, and Mg) crucial for crop development and the secondary nutrients (Fe, Cl, Mn, Bo, Cu, and Mo) critical for crops in smaller quantities [19, 20]. The list of elements and their functions are explained in Table 2.
| Element | Functions |
|---|---|
| Carbon | Integral of all organic compounds found in plants. |
| Hydrogen | Component of all organic compounds of which carbon is a constituent. |
| Oxygen | Constituent of many organic compounds in plants. And intricate in anion exchange amid external medium and roots. It is a terminal H+ acceptor in aerobic respiration. |
| Nitrogen | Constituent of a large number of necessary organic compounds, including amino acids, proteins, coenzymes, nucleic acids, and chlorophyll. It is also present as a component of coenzymes like FAD, NAD, and NADP, etc. |
| Phosphorus | Constituent of many important organic compounds, including sugar phosphates in photosynthesis, ATP, nucleic acids, phospholipids, and certain coenzymes. |
| Potassium | Essential for stomatal opening and translocation of sugar. Acts as a coenzyme or activator for numerous enzymes (e.g., pyruvate kinase). Protein synthesis requires high potassium levels. |
| Sulphur | Present in numerous organic compounds, as well as amino acids and proteins. Coenzyme A, biotin contain sulphur and the vitamins thiamine. |
| Magnesium | A vital portion of the chlorophyll molecule and crucial for the activation of many enzymes, including those involved in ATP bond breakage. Essential to maintain ribosome structure. |
| Calcium | Originate inside cell walls as calcium pectate that cements together primary walls of head-to-head cells. Required to maintain the integrity of the membrane and is part of the enzyme α-amylase. Interferes with the ability of magnesium to activate enzymes. |
| Iron | Essential for chlorophyll synthesis and is a vital portion of the cytochromes. Electron carriers in photosynthesis and respiration. It is a crucial part of ferredoxin and possibly nitrate reductase. Activates certain other enzymes. |
| Manganese | It helps activate one or more enzymes in fatty acid synthesis, the enzymes responsible for DNA and RNA formation, and the isocitrate dehydrogenase enzyme. Contributes directly in photosynthesis and maybe in chlorophyll formation. |
| Chlorine | Crucial for photosynthesis, where it acts as an enzyme activator during the production of oxygen from water. Effects of deficiency on roots suggest additional functions. |
| Boron | Function in plants not well understood. It may be essential for carbohydrate transport in the phloem. |
| Zinc | Required for the formation of the indoleacetic hormone acid. Activates the alcohol dehydrogenase enzyme, lactic acid dehydrogenase, glutamic acid dehydrogenase, and carboxypeptidase |
| Copper | Electron carrier and a portion of certain enzymes. A portion of plastocyanin, which is involved in photosynthesis, and also of polyphenol oxidase and possible nitrate reductase. May be involved in N2 fixation. |
| Molybdenum | Plays as an electron carrier in the conversion of nitrate to ammonium and is also essential for N2 fixation. |
Monitoring and controlling are two important factors in hydroponics systems for successfully growing plants. Automation and operation control is divided into four categories such as sensors, remote management, equipment control, analytical, and machine learning. The main automation and operation control involved in hydroponics is shown in Figure 3. Nowadays, commercial hydroponics systems are automated using a microcontroller, which provides more flexible and efficient operation than manual operation. The controllers can be used on large-scale crops in a greenhouse with small conversions. At present, the controllers used in setting up hydroponics systems can monitor activation and deactivation of lighting, ventilation, fan, and humidifier. In addition, some of the controllers used more specifically to collect the values of environmental factors and automatically adjust them to favorable levels of humidity of the growing area, the acidity of the nutrient solution, and the operation time of artificial light. Some of the systems can adjust desired fertilizer dosages, and these are automatically injected into the tank with the touch of a button. These parameters are monitored by implementing well-designed sensors and conditioning circuits. The adoption of an inexpensive controller has the capacity to solve problems caused by simultaneous climate and necessary conditions at a reasonable cost [21, 22]. Systems like Autogrow, MultiGrow, IntelliDose, IntelliClimate, LEAF, and SUPERCLOSET available in the market provide automation, monitoring, and control of the environmental parameters [23].
Figure 3: Automation and operation control involved in hydroponics farming
There are many advantages of the hydroponics system for growing crops than the soil-grown crops. But there is no guarantee regarding the nutritional quality of produce since the quality of plants depends on water quality, nutrient solution, and environmental conditions. Comparative studies of the nutritional content of food grown hydroponically with that of produce grown in soil showed mixed results. Various studies claimed that hydroponically grown crops have better quality than those from soil cultivation, while others indicated that soil-grown plants have acceptable quality in nutrient level. Table 3 represents some examples of studies about a nutritional comparison between hydroponics and soil-grown crops. Treftz and Omaye explain that hydroponically grown strawberries showed higher ascorbic acid, alpha-tocopherol, total phenolic, brix, and moisture content than soil-grown ones. Based on the results obtained from different studies, it can be assumed that the nutritional quality of plants can be enhanced using a hydroponics system by tight control over the entire process of cultivation [24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36].
| Properties | Hydroponically grown (+) | Soil-grown (+) |
|---|---|---|
| Ascorbic acid | Strawberries [25], Waldman’s Dark Green Lettuce, Red Lollo Antago Lettuce, Red Romaine Annapolis Lettuce and Butterleaf Lettuce [26], Basil [27] | Raspberries [25] |
| Alpha-tocopherol | Strawberries and Raspberries [25], Waldman’s Dark Green Lettuce, Red Lollo Antago Lettuce and Red Romaine Annapolis Lettuce [26], Basil [27] | Butterleaf Lettuce [26] |
| Carotenoids | Curly lettuce [28] | |
| Chlorophyll | Okra and Mong [29] | Pea [29] |
| Protein | Pea [29] | Okra and Moong [29] |
| Fructose | Strawberries [25] | |
| Glucose | Raspberries [25] | Strawberries [25] |
| Total sugar | Moong [29] | Pea and Okra [29] |
| Total phenolics | Lettuce [30], Lollo rosso and Butterhead lettuce [31], Red kale and Cherry tomato [32], Strawberries [25], Spinach [33], Basil [27], Ligularia fischeri [34] | Red oak leaf [31], Basil, Chard, Parsley, Bell pepper, and Cucumber [32], Raspberries [25], Sage [35] Common Dandelion [36] |
| Total flavonoids | Chard, Red kale, Squash and Cherry tomato [32], Spinach [33], Yarrow root [36], Ligularia fischeri [34] | Basil, Parsley, Bell pepper and cucumber [32], Sage [35], Yarrow leaf [36], Ligularia fischeri [34] |
| Brix | Raspberries [25] | Strawberries [25] |
| % Moisture | Strawberries and Raspberries [25] |
Two aspects help increase the crop yield; the first one increases the amount of plant per area, and the second is to increase the production per plant. In hydroponics, the plants can be grown in vertical layers, so the number of plants increases by the increase in the number of layers, whereas in soil, crops are grown in only one layer. Production per plant is rising in hydroponics as plants are provided with adequate nutrients, light, and CO2. There are some scientifically proven examples mentioned in Table 4. Barbosa et al. study showed that hydroponically grown lettuce (41 kg/m2/y) obtained a higher yield as compared to soil-grown lettuce (3.9 kg/m2/y). Based on the results obtained from different studies, it can be assumed that the nutritional quality of plants can be enhanced using a hydroponics system by tight control over the entire process of cultivation [37, 38, 39, 40, 41, 42, 43, 44, 45, 46].
| Crops | Total yield | Reference | |
|---|---|---|---|
| Hydroponics | Soil | ||
| Lettuce | 41 kg/m2/y | 3.9 kg/m2/y | [37] |
| Lamb’s Lettuce | 1585±304 g/m2 | 1203±304 g/m2 | [38] |
| Chard | 246.78 g/plant | 228.22 g/plant | [32] |
| Eggplant | 7.36 kg/m2 | 6.47 kg/m2 | [39] |
| Wheat | 1828 kg/acre in 7 days | 1762 kg/acre in 7 days | [40] |
| Cantaloupe var. Alpha | 23.18 t/ha | 12.55 t/ha | [41] |
| Cantaloupe var. Emerald | 23.18 t/ha | 7.73 t/ha | [41] |
| Cantaloupe var. Sin | 23.18 t/ha | 4.44 t/ha | [41] |
| Tomato var. Miramar | 7844 g/plant | 5118 g/plant | [42] |
| Cherry tomato | 4741.83 g/plant | 3513.58 g/plant | [32] |
| Basil | 388.14 g/plant | 326.64 g/plant | [32] |
| Parsley | 414.64 g/plant | 342.04 g/plant | [32] |
| Cayenne pepper | 10.8 Fruits/plant | 8.6 fruits/plant | [43] |
| Sage | 2286 g/m2 | 863 g/m2 | [44] |
| German chamomile | 3015 g/m2 | 962 g/m2 | [44] |
| Jordanian chamomile | 906 g/m2 | 411 g/m2 | [44] |
| Thyme | 1283 g/m2 | 518 g/m2 | [44] |
| Mint | 3208 g/m2 | 1320 g/m2 | [44] |
| Strawberry | 85 Fruits | 70 Fruits | [25] |
| Sweet pepper | 10.95 kg yield/m2 | 9.40 kg yield/m2 | [45] |
| Bell pepper | 1277.88 g/plant | 834.54 g/plant | [32] |
| Cucumber | 4727.38 g/plant | 4427.38 g/plant | [32] |
| Zucchini | 21 fruit/plants | 17 fruits/plants | [46] |
Hydroponics is considered a promising technology despite the high initial cost and demand for energy. Insight of initial capital expenditure is high; this technology is the best because the operational cost is minimal compared to conventional farming. It reduces labor costs and maintenance costs by sophisticated control devices [37]. According to UNDP in 1996, total expenses used to produce hydroponic celery was 2.31 US$ cost/m2, whereas net income was 28.55 US$/m2 [47]. Studies explained that in hydroponics cultivation, the profit is more than the cost of cultivation for growing crops. For example, capital cost (includes the cost of land, greenhouse, irrigation system, and project consultancy) required 6.1 lakhs/year (approx.) and operational cost (includes polybags, coco pear, nutrients per cropping cycle, seeds, electricity, and salary for employees) required is 9.0 lakhs/year (approx.) to grown tomato hydroponically, whereas revenues are 30/year (approx.) [48].
Enthought hydroponic cultivation is developed to provide plants with the best growing conditions to attain optimum yield. But some stresses can occur on plants as soil although at different ranges, in more pervasive and severe conditions. In hydroponics, stresses can be biotic and abiotic. Abiotic stresses are caused by temperature, improper nutrient supply, salinity, drought, insufficient or excessive oxygen or carbon dioxide, and light. Biotic stresses can be caused by pests and algae [49].
8.1 Challenges due to abiotic stressesThe impact of abiotic stresses can be easily applied to shoot and root tissues because of its rapid accessibility in hydroponic cultivation [50]. The abiotic stresses mainly affect the composition of the plants. For example, Gent [51] explained that temperature affects nutrient uptake and metabolism in plants. Cool temperature decreased specific leaf area, total reduced nitrogen and nitrate content of the lettuce. The warm temperature increased dry matter, sugar, malic acid, and potassium content in the lettuce tissues. Improper nutrient supply is another abiotic stress that has both positive and negative effects on plants. Amongst the abiotic stresses, salinity is one of the major limiting factors for plant growth in hydroponics. Some studies showed that salinity decreased root water uptake by osmotic effect leads to water stress. It also showed that hydroponic salinity positively affects tomato fruit quality, whereas plant growth and fruit production were negatively affected [52]. Zha et al. [53] explained that the increase in the light intensity and continuous light duration leads to enhancing the oxidative stress degree reflected by ROS production and lipid peroxidation.
8.2 Challenges due to biotic stresses 8.2.1 Pest and its controlThe chances of pest infestation are more in hydroponics as the entire system has an ideal environment for various types of pests. The control of different kinds of pests is considerably varied from one to another. So, it is crucial to be familiar with pests and their control measures. In case of hydroponics, there is nothing unique about pest control. The same procedures are used to prevent insects in soil-grown plants. It is essential to maintain the daily monitoring procedures regarding pest incidence considered damaging, and they are economically necessary to control [10]. The common pests in hydroponics crop production are spider mites, aphids, thrips, whiteflies, and fungus gnats [54]. The best pest management program mainly depends on prevention rather than control [55].
8.2.2 Algae and its managementAlgal growth in a hydroponics system is noticed mainly due to light and nutrient availability, especially with the recirculating system (example: nutrient film technique). The algae can create problems like water supply, competitors for nutrient absorption with plants, and certain algae produce toxins that can inhibit or stop crop growth. Overall, the occurrence of algae has more negative effects on crop yield in hydroponics systems [56, 57]. In a hydroponics system, the presence of algae attracts two species of flies, such as Bradysia spp. (Diptera: Sciaridae) and Scatella stagnalis (Diptera: Ephydridae) [58]. There are a few conditions to be maintained in hydroponics for controlling algal growth. They are as follows: (a) coverage of physical structures by suitable plastic films have been reported as efficient for algal control, (b) nutrient solutions should be kept in the dark and cold conditions. (c) after each crop cycle, reused plastic system components should be sanitized. (d) common sanitizers include chlorine bleach solution, Hydrogen peroxide (H2O2), quaternary ammonium chloride, phenolic materials, and cryptocidal soaps.
The magnificent yield quality and quantity with hydroponics techniques compared to traditional soil-based farming has enormously attracted farmers and markets globally and is flourishing in India. According to Global Marketing Insights Journal under section food, nutrition, and animal feed, the global hydroponics vegetable market size is likely to grow with a high CAGR by 2024. Hydroponically grown vegetables can be cultivated corresponding to the market’s demand-supply and price. It helps substantially swelling the value of harvest for the manufacturers, thereby reducing the carbon footprint and expenses tangled between the distribution channels [59].
9.1 Global perspectiveThere is a substantial growth opportunity in the global hydroponics market. The key geographical regions served by the hydroponics industry are America, Europe, and the Asia Pacific. These regions are additionally segmented, listing the major countries in each area. The U.S. is recognised to be the largest market for the hydroponics industry, accounting for over 33% of net market revenue as of 2014, followed by Germany and Canada [60]. Major companies have been trying to arrive in this space, either by developing hydroponics components or investing in crop cultivation technology. Hydroponics market is separated into two segments-system input providers and hydroponics crop producers. They are led by Bowery, Inc., Metropolis Farms, Inc., Lufa Farms, FreshBox Farms, Cropking, Inc., Triton Foodworks, Hydroherbs, Evergreen Farm Oy, GrowUp Urban Farm, Urban Harvest, Signify Holdings (Netherlands), Heliospectra AB (Sweden), American Hydroponics (US), Scotts Miracle Gro (US), LumiGrow (US), and Argus Control Systems (Canada), are the major hydroponics players worldwide. And the key players in the hydroponics crop producer market include Hydroponics Farms (UAE), Aerofarms (US), Terra Tech Corp (US), Triton Foodworks Ltd. (India), Urban cultivator (Canada), Village Farms (Canada), Green Sense Holdings (US), and Iron Ox (US) [61].
9.2 Indian perspectiveHydroponics farming is setting uproots all across India. India has been lagging in the race of implementing hydroponics as a technology. But it has been picking up in a big way in the past decade. Several farmers across the length and breadth of India have been trying to experiment and learn the science of hydroponics. Due to the dynamics of the Indian market, hydroponics farming in India has been limited to the growth of exotic vegetables, which gives better economic viability. In India, the government promotes hydroponics by offering subsidies for fodder growing through hydroponics.
Additionally, increasing government spending on locally grown food is also expected to foster the growth of the global hydroponics market in upcoming years [62]. Sakina Rajkotwala and Joshua Lewis of Herbivore Farms have come into focus in the last year. In Manori, Linesh Pillai started Terra Farms as a pilot project before taking the idea countrywide. Delhi has Triton Foodworks; Noida has Nature’s Miracle; Chennai has Sriram Gopal’s Future Farms and Rahul Dhoka’s Acqua Farms; and Gurugram-based company, Barton Breeze, has six farms across Haryana, Rajasthan, Uttar Pradesh, and Uttarakhand [63].
Hydroponics is the fastest increasing area of agriculture and has a great future in food production. It has a bright future as many under-developed and developing countries adopt it for food production in limited space. Tokyo has started hydroponics rice production to feed people. Hydroponics also has been used successfully to grow large quantities of berries, citrus fruits, and bananas in a country like Israel, which has a dry and arid climate. This technique has the ability to feed millions in areas where both water and crops are in scarcity, like Africa and Asia. In EU, this technology is extensively practiced in producing vegetables and eggplant, peppers, melons, strawberries, and herbs. In the USA, high-quality garden type vegetables, tomato, cucumber, and especially lettuce are grown extensively. Hydroponics is an appropriate technique for biological research, and it is the best platform for analyzing the interactions between multiple factors that influence plant growth. This technology shows a promising result in the space program's future, as NASA has extensive hydroponics research plans in place, especially current and future space exploration long-term colonization of the Moon or Mars. Hydroponics could play a vital role in the future of spaceOO exploration as we haven’t yet found any soil that can support life in space and also the logistics of transporting soil via space shuttles seems impractical [12, 64].
Hydroponics is emerging to be a promising approach in the design of supportable, eco-friendly technology to improve polluted soil sites and prevent further degradation of the soil system. Even though initial capital expenditure is high, this technology is the best because the operational cost is minimal compared to conventional farming. It reduces the labour cost, and sophisticated control devices decrease maintenance costs. It also helps eliminate the most important concerns about food safety by eradicating problems like soil or water contamination and pesticide residues. The hydroponics industry is expected to grow exponentially in the near future throughout the world.
This work was supported by a HiMedia Laboratories Private Limited, Mumbai, India, and University Grant Commission, Government of India. All authors are grateful to Dr. Savita V. Bhave for their excellent support in editing the draft. This has reference to our manuscript all the authors involved in this paper declare that the University Grant Commission did funding the present work, Government of India, under the Scheme UGC-NET JRF program grant number is 1382/(OBC)(NET-JUNE2015).
