REVIEW ARTICLE

Growing Beyond Soil: The Future of Farming with Hydroponics

Tarun Kumar Patel

Department of Biotechnology, Sant Guru Ghasidas Govt. P.G. College, Kurud, Dhamtari, Chhattisgarh, India.

*Corresponding Author Email- tarun_rgh@yahoo.co.in

Introduction

Hydroponics offers a compelling alternative to these traditional methods by eliminating the dependency on soil and reducing water usage significantly. In a hydroponic system, plants receive their nutrients from a carefully balanced solution delivered directly to their roots. This direct delivery method ensures optimal nutrient uptake and minimizes water wastage, with studies showing that hydroponic systems can use up to 90% less water than traditional soil-based farming (Rajaseger  et al. 2023). This efficiency is crucial for regions facing water shortages and supports sustainable agricultural practices. The controlled environment of hydroponic systems allows for year-round cultivation, independent of seasonal changes and adverse weather conditions. This capability is particularly advantageous in urban areas where space is limited and traditional farming is impractical (Rajaseger et al. 2023). Vertical farming, a type of hydroponic system, exemplifies this benefit by utilizing vertically stacked layers to grow crops, maximizing space usage in densely populated cities. By bringing food production closer to urban centers, hydroponics can also reduce the carbon footprint associated with long-distance transportation of produce (Kabir et al. 2023; Al-Kodmany 2018).

This review explores hydroponics, a soil-less method of growing plants using nutrient-rich water solutions, highlighting its efficiency and sustainability as a solution to traditional agriculture challenges like soil degradation and water scarcity. It covers the evolution of hydroponic systems, their various types, advantages, and the challenges faced. The review includes case studies of successful implementations, technological innovations enhancing hydroponics, and its environmental benefits, concluding with future prospects and trends in this transformative agricultural practice.

Methodology

This review aims to provide a thorough examination of the future of farming with hydroponics by exploring the latest advancements and trends in the field. A comprehensive literature search was conducted using reputable databases such as Google Scholar, PubMed, Scopus, and Web of Science. The search focused on documents published between 2009 and 2024 to capture recent developments. Keywords such as "hydroponics," "soilless farming," "vertical farming," "sustainable agriculture," and "urban agriculture" were used in the search strategy. The inclusion criteria centered on peer-reviewed articles, reviews, and case studies, while outdated studies were excluded unless they provided essential historical context. The search results were systematically categorized, focusing on key areas including technological advancements, environmental impacts, and future trends. A rigorous critical analysis was performed, evaluating the methodologies, results, and conclusions of the selected studies. Gaps in the literature and areas of consensus or disagreement were identified to inform future research directions.

History and Evolution of Hydroponics

Origins and Early Developments

Hydroponics, the method of growing plants without soil, traces its origins back to ancient civilizations. The Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World, are believed to have employed early hydroponic techniques, using a system to deliver nutrient-rich water to plants Similarly, the ancient Aztecs practiced a form of hydroponics with their floating gardens, or "chinampas," where crops were grown on rafts in shallow lakes, receiving nutrients directly from the water (Ozier-Lafontaine & Lesueur-Jannoyer 2014).

The scientific foundation of hydroponics began to take shape in the 17^th century. Researchers like Sir Francis Bacon, who wrote "Sylva Sylvarum" in 1627, hinted at soil-less growing methods (Ozier-Lafontaine & Lesueur-Jannoyer 2014). However, it wasn't until the 19^th and early 20^th centuries that significant strides were made. In 1860, German botanists Julius von Sachs and Wilhelm Knop developed nutrient solutions that allowed plants to grow without soil, providing a clearer understanding of the essential elements required for plant growth (Kumar & Saini 2020).

Milestones in Hydroponic Technology

The 20^th century witnessed several key milestones that propelled hydroponics into modern agricultural practice:

1.     1930s - Coining of the Term "Hydroponics": Dr. William Frederick Gericke of the University of California is credited with coining the term "hydroponics" from the Greek words "hydro" (water) and "ponos" (labor) (Rajaseger et al. 2023). He successfully grew large tomato plants using only nutrient solutions, demonstrating the potential of this method for commercial agriculture (Stegelmeier et al. 2022; Al-Kodmany 2018).

2.     1940s - Military and NASA Experiments: During World War II, the U.S. military used hydroponics to supply fresh produce to troops stationed on non-arable Pacific islands. This practical application showcased hydroponics' potential in areas unsuitable for traditional farming. Later, NASA explored hydroponics as part of its Controlled Ecological Life Support System (CELSS) program, aiming to provide astronauts with fresh food during long space missions.

3.     1960s-1970s - Advancements in Hydroponic Systems: Innovations such as the Nutrient Film Technique (NFT) by Dr. Allen Cooper in the late 1960s and the development of Deep Water Culture (DWC) systems in the 1970s marked significant technological advancements (Cooper 2002; Janick 1983). These systems improved nutrient delivery and oxygenation, enhancing plant growth and yield.

4.     1980s-1990s - Commercial Adoption and Vertical Farming: The commercial adoption of hydroponics grew in the 1980s, with large-scale operations in Europe and the United States producing high-quality vegetables and herbs. The concept of vertical farming, popularized in the 1990s, utilized hydroponic systems to maximize space in urban environments, leading to the development of multi-layered growing structures (Okomoda et al. 2023; Chatterjee et al. 2020).

5.     2000s-Present - Technological Integration and Sustainability: The 21^st century has seen hydroponics integrate with advanced technologies such as automation, Internet of Things (IoT), and LED lighting. These innovations have optimized growth conditions, reduced energy consumption, and made hydroponics more accessible. Additionally, the focus on sustainability has driven research into renewable energy sources and eco-friendly practices within hydroponic systems (Rajaseger et al. 2023; Thakur & Malhotra 2023; Tatas et al. 2022).

Today, hydroponics continues to evolve, offering a viable and sustainable alternative to traditional agriculture. With ongoing research and technological advancements, hydroponics is poised to play a critical role in addressing global food security challenges and promoting sustainable farming practices.

Key Advantages of Hydroponic Farming

Efficient Use of Water and Nutrients

One of the most significant advantages of hydroponic farming is its efficient use of water and nutrients (Fig.1). Traditional soil-based agriculture can be wasteful, with much of the water and nutrients lost to runoff and evaporation (Kumawat et al. 2021). In contrast, hydroponic systems deliver nutrients directly to the plant roots through a controlled environment, ensuring optimal uptake. This method can reduce water usage by up to 90% compared to conventional farming (Rajaseger et al. 2023). Nutrient solutions are recirculated, minimizing waste and ensuring that plants receive a balanced mix of essential minerals. This efficiency is especially crucial in regions facing water scarcity, making hydroponics a sustainable and environmentally friendly alternative to traditional farming (Rajaseger et al. 2023).

Year-Round Crop Production

Hydroponic farming allows for continuous, year-round crop production, independent of seasonal changes and adverse weather conditions (Rajaseger et al. 2023). By creating controlled environments with regulated temperature, humidity, and light, hydroponic systems can maintain ideal growing conditions throughout the year. This capability ensures a consistent supply of fresh produce, which is particularly beneficial in regions with harsh climates or limited growing seasons. The ability to produce crops continuously can also stabilize market prices and reduce the volatility associated with seasonal agricultural production. Moreover, it can help meet the increasing demand for fresh food in urban areas, contributing to food security and sustainability (Gómez et al. 2019; Aires 2018).

Space Utilization

Hydroponic farming is highly efficient in terms of space utilization (Rajaseger et al. 2023; Velazquez-Gonzalez et al. 2022). Traditional farming requires vast amounts of arable land, which is becoming increasingly scarce due to urbanization and environmental degradation (Wang 2022). Hydroponic systems, especially vertical farming setups, can maximize space by stacking multiple layers of crops in a controlled environment (Gürsu 2024). This vertical approach is ideal for urban areas where space is limited and land costs are high. Hydroponic farms can be established in a variety of settings, from rooftop gardens to repurposed warehouses, making it a versatile solution for urban agriculture (Zaręba et al. 2021; Benke & Tomkins 2017).

Scalability

Scalability is another key advantage of hydroponics. These systems can be scaled up or down to meet specific needs, from small-scale home gardens to large commercial operations. The modular nature of hydroponic systems allows for easy expansion, enabling farmers to increase production capacity as demand grows. This flexibility makes hydroponics an attractive option for both small-scale producers and large agricultural enterprises. Furthermore, the controlled environment of hydroponic systems reduces the risk of pests and diseases, leading to higher crop yields and lower reliance on chemical pesticides and herbicides (Rajaseger et al. 2023).

Fig.1. The advantages of hydroponic farming

In conclusion, hydroponic farming offers numerous advantages over traditional soil-based agriculture. Its efficient use of water and nutrients, ability to support year-round crop production, and excellent space utilization and scalability make it a sustainable and innovative solution for modern agriculture. As global challenges such as water scarcity, climate change, and urbanization continue to impact food production, hydroponics provides a viable and forward-thinking approach to meeting the world's growing food needs.

Types of Hydroponic Systems

Hydroponic farming encompasses several innovative techniques, each offering unique benefits and suited to different types of crops and growing conditions. Here’s an overview of the most common hydroponic systems (Fig.2):

Nutrient Film Technique (NFT)

The Nutrient Film Technique (NFT) is one of the most widely used hydroponic systems. In NFT, a thin film of nutrient-rich water continuously flows over the roots of plants housed in channels or tubes. This film provides essential nutrients while also allowing the roots to access oxygen. The slight angle of the channels ensures that the nutrient solution flows smoothly from one end to the other, preventing stagnation. NFT systems are particularly popular for growing leafy greens, herbs, and other fast-growing plants (Souza et al. 2023; Wheeler et al. 1990). They are highly efficient in terms of water and nutrient use and can be easily scaled to different sizes, making them ideal for both small and large operations (Rajaseger et al. 2023).

Deep Water Culture (DWC)

Deep Water Culture (DWC) is a straightforward and effective hydroponic method where plant roots are suspended in a nutrient-rich water solution. The roots are fully submerged in the solution, and oxygen is provided through air stones and pumps that aerate the water. This continuous supply of oxygen and nutrients promotes rapid growth and robust plant health. DWC systems are commonly used for growing larger plants such as tomatoes, peppers, and cucumbers. They require minimal maintenance and are relatively inexpensive to set up, making them a popular choice for beginners and hobbyists. However, maintaining adequate oxygen levels is crucial to prevent root rot and ensure healthy plant growth (Pattillo et al. 2022; Verdoliva et al. 2021).

Fig. 2. The most common hydroponic systems

Aeroponics

Aeroponics is an advanced hydroponic technique where plant roots are suspended in the air and periodically misted with a nutrient solution. This method provides the roots with ample oxygen while delivering nutrients directly, promoting faster growth and higher yields (Garzón et al. 2023). Aeroponics systems can achieve remarkable efficiency in water and nutrient use, as the misting process reduces waste (Lakhiar et al. 2018). Additionally, the high oxygen levels around the roots can lead to increased nutrient absorption and plant vigor (Eldridge et al. 2020). Aeroponics is often used for high-value crops such as herbs, leafy greens, and medicinal plants (Kim et al. 2024). Despite its advantages, aeroponics systems can be more complex and costly to set up and maintain, requiring precise control over misting cycles and nutrient delivery (Niu & Masabni 2022).

Vertical Farming Systems

Vertical farming systems are designed to maximize space efficiency by growing plants in vertically stacked layers, often within controlled indoor environments. These systems can incorporate various hydroponic techniques, such as NFT, DWC, or aeroponics, to optimize growth conditions. Vertical farming is particularly well-suited for urban agriculture, where space is limited, and the demand for fresh produce is high. By utilizing vertical space, these systems can produce large quantities of food in a relatively small footprint. Additionally, the controlled environment of vertical farms allows for year-round production, independent of weather and seasonal changes. Vertical farming systems often integrate advanced technologies such as LED lighting, climate control, and automation to enhance efficiency and productivity. This innovative approach to farming addresses the challenges of urbanization and food security by bringing agriculture closer to consumers and reducing the environmental impact of food transportation (Van Gerrewey et al. 2022; Birkby 2016).

A comparison of different hydroponic systems, including Nutrient Film Technique (NFT), Deep Water Culture (DWC), Aeroponics, and Vertical Farming Systems is given in the Table1.

In summary, hydroponic systems offer diverse and adaptable solutions for modern agriculture. Each technique - NFT, DWC, aeroponics, and vertical farming - provides distinct advantages, catering to different crops, environments, and production scales. As technology continues to advance, these systems will likely become even more efficient and accessible, playing a crucial role in sustainable and resilient food production.

Challenges and Considerations

Initial Setup Costs

One of the primary challenges associated with hydroponic farming is the high initial setup costs. Establishing a hydroponic system requires significant investment in equipment such as grow lights, pumps, nutrient delivery systems, and climate control technologies. Additionally, specialized structures like greenhouses or controlled environment agriculture (CEA) facilities may be needed to optimize growing conditions. While these costs can be a barrier for small-scale farmers and hobbyists, they can be mitigated over time by the system's higher yields and efficiency. However, securing the initial capital can still be a substantial hurdle, and careful planning and budgeting are essential to ensure the project's financial viability (Quagrainie et al. 2017).

Table 1. Comparison of different hydroponic systems.

Technical Expertise Required

Hydroponic farming demands a higher level of technical expertise compared to traditional soil-based agriculture. Growers must understand the intricacies of nutrient formulations, pH levels, water quality, and system maintenance to ensure optimal plant health and productivity. The precision required in managing these factors can be daunting for beginners. Furthermore, advanced hydroponic systems often integrate technology such as automation and IoT, which necessitates knowledge in operating and troubleshooting electronic and mechanical components. As a result, growers may need to invest in education and training or hire skilled personnel, adding to the overall operational costs and complexity (Rajaseger et al. 2023; Velazquez-Gonzalez et al. 2022).

Potential Environmental Impacts

While hydroponics offers numerous environmental benefits, such as reduced water usage and minimized need for pesticides, it also presents certain environmental challenges. The production and disposal of hydroponic growing media, such as rock wool or coconut coir, can have environmental impacts if not managed properly. Additionally, the use of synthetic nutrients in some hydroponic systems can contribute to nutrient runoff and pollution if not carefully controlled. Energy consumption is another consideration, particularly in systems that rely heavily on artificial lighting and climate control. Although advancements in renewable energy and energy-efficient technologies are mitigating these impacts, growers must still be mindful of their energy use and seek sustainable practices wherever possible (Fathidarehnijeh et al. 2024; Sela Saldinger et al. 2023; Velazquez-Gonzalez et al. 2022; Aires 2018; Barrett et al. 2016).

In conclusion, while hydroponic farming holds great promise for sustainable and efficient agriculture, it is not without its challenges. High initial setup costs, the need for technical expertise, and potential environmental impacts must be carefully managed to realize the full benefits of this innovative farming method. By addressing these considerations through strategic planning, education, and sustainable practices, hydroponic farming can continue to evolve and play a vital role in the future of global food production.

Case Studies and Examples

Successful Implementations in Commercial Agriculture

1.      Gotham Greens (USA)

Gotham Greens is a leading example of commercial hydroponic farming in the United States. Founded in 2009, the company operates several urban greenhouses across cities like New York, Chicago, and Baltimore. Utilizing advanced hydroponic systems, Gotham Greens produces a variety of leafy greens and herbs year-round. Their greenhouses use 95% less water than traditional soil-based farming and are powered by renewable energy sources. By employing precise climate control and integrated pest management, Gotham Greens ensures high-quality produce while minimizing environmental impact. Their success demonstrates the viability of hydroponics in urban settings, providing fresh, locally grown produce to nearby communities and reducing food miles significantly (Min et al. 2023; Proksch & Ianchenko 2023; Darling 2020; Sembin et al. 2019).

2.      Bright Farms (USA)

Bright Farms is another successful commercial hydroponic farming company based in the United States. The company builds and operates greenhouse farms in close proximity to urban areas to supply local supermarkets with fresh, sustainably grown produce. By using hydroponic systems, Bright Farms maximizes resource efficiency, cutting water usage by up to 80% compared to conventional agriculture. Their greenhouses also reduce the need for long-distance transportation, ensuring that produce is fresher and has a smaller carbon footprint. Bright Farms’ model has proven scalable and economically viable, contributing to more sustainable food systems (Schoch 2022).

Urban Farming Initiatives and Their Impact

1.      Sky Greens (Singapore)

Sky Greens is an innovative urban farming initiative in Singapore, where land is scarce, and food security is a major concern. Established in 2012, Sky Greens operates the world's first commercial vertical farm using hydroponics. The farm utilizes rotating vertical towers that allow for efficient use of space and resources. By growing vegetables in a controlled environment, Sky Greens can produce crops year-round, unaffected by weather conditions. The vertical farming system uses minimal land and reduces water consumption by up to 90%. Sky Greens has successfully integrated hydroponics into Singapore's urban landscape, contributing to local food production and reducing the city-state's reliance on imported produce (Chatterjee et al. 2020; Milestad et al. 2020; Wood et al. 2020; Al-Kodmany 2018; Ali & Srivastava 2017).

2.      Lufa Farms (Canada)

Lufa Farms, based in Montreal, Canada, is a pioneering urban farming initiative that uses hydroponic systems to grow fresh vegetables on rooftop greenhouses. Founded in 2009, Lufa Farms aims to provide sustainable and locally grown produce to urban residents. Their rooftop greenhouses utilize hydroponic techniques to maximize space and resource efficiency, producing high yields with minimal environmental impact. By situating their farms on rooftops, Lufa Farms makes efficient use of urban space that would otherwise go unused. The produce is delivered directly to consumers through a subscription model, ensuring freshness and reducing food waste. Lufa Farms' innovative approach to urban agriculture has inspired similar projects worldwide and highlights the potential of hydroponics to transform urban food systems.

3. The Högdalen urban farm (Sweden)

Milestad et al. (2020) explores the multifaceted success of the Högdalen urban farm. Situated in Stockholm, Sweden, this urban farm exemplifies a model of sustainability by integrating ecological, economic, and social dimensions into its operations. They find the farm's innovative practices, such as organic farming techniques and local food production, contribute to food security and environmental stewardship. Moreover, the farm fosters community engagement and education, creating a resilient social fabric that supports sustainable urban living. The study underscores the potential of urban farms to enhance sustainability in metropolitan areas, offering valuable insights for policymakers and urban planners.

These case studies illustrate the diverse applications and significant impact of hydroponic systems in both commercial agriculture and urban farming. By leveraging technology and sustainable practices, these initiatives address key challenges such as resource scarcity, food security, and environmental sustainability, paving the way for the future of agriculture.

Technological Innovations in Hydroponics

Automation and Internet of Things (IoT) integration have revolutionized hydroponic farming, making it more efficient, scalable, and user-friendly. These technologies enable precise control over various environmental factors such as nutrient delivery, pH levels, humidity, and temperature, ensuring optimal growing conditions for plants.

1.    Automation:

Nutrient Delivery Systems: Automated nutrient delivery systems can precisely control the concentration and timing of nutrient solutions provided to plants. These systems use sensors to monitor the nutrient levels and adjust the delivery in real-time, ensuring that plants receive the exact amount of nutrients needed for optimal growth (Sangeetha & Periyathambi 2024).

Climate Control: Automated climate control systems regulate temperature, humidity, and CO₂ levels within the growing environment. This ensures consistent and ideal conditions, which are crucial for maximizing plant health and yield. These systems often include automated ventilation, heating, and cooling mechanisms (Soussi et al. 2022).

Watering and Irrigation: Automated watering systems in hydroponics can ensure that plants receive the correct amount of water at the right intervals, reducing water waste and preventing over- or under-watering (Ghiasi et al. 2024; Rajendran et al. 2024).

2.     IoT Integration:

Real-Time Monitoring: IoT devices equipped with sensors can provide real-time data on various parameters such as nutrient concentration, pH levels, light intensity, and environmental conditions. This data can be accessed remotely through smartphones or computers, allowing farmers to monitor and manage their hydroponic systems from anywhere (Rahman et al. 2024).

Data Analytics: IoT systems can collect and analyze large amounts of data to optimize growing conditions. By analyzing trends and patterns, these systems can make predictive adjustments to nutrient delivery and environmental controls, enhancing efficiency and productivity (Rahman et al. 2024).

Alerts and Notifications: IoT integration allows for instant alerts and notifications if any parameters fall outside the optimal range. This enables quick intervention to prevent potential issues and maintain a stable growing environment (Rahman et al. 2024).

Advances in LED Lighting for Plant Growth

Advances in LED lighting technology have significantly improved the efficiency and effectiveness of hydroponic systems. LEDs offer numerous benefits over traditional lighting methods such as high-pressure sodium (HPS) and fluorescent lights, making them a preferred choice for modern hydroponic farms. The key technological innovations/advances in hydroponics along with their advantages and challenges are given in the Table 2.

Energy Efficiency: LEDs are highly energy-efficient, consuming up to 50% less electricity compared to traditional lighting systems. This reduces operational costs and makes hydroponic farming more sustainable (Poulet et al. 2014).

Customizable Light Spectra: Modern LED grow lights can be tailored to emit specific wavelengths of light that are most beneficial for plant growth. Different stages of plant growth (e.g., vegetative and flowering) require different light spectra, and LEDs can be adjusted to provide the optimal light conditions for each stage (Rahman et al. 2021; Sena et al. 2024).

Reduced Heat Emission: LEDs produce significantly less heat than traditional lighting systems, reducing the need for additional cooling and ventilation. This not only lowers energy consumption but also minimizes the risk of heat stress on plants (Barceló-Muñoz et al. 2022; Lanoue et al. 2022).

Longevity and Durability: LED lights have a longer lifespan compared to traditional bulbs, often lasting up to 50,000 hours or more. This reduces the frequency of replacements and maintenance costs (Richter et al. 2019).

Compact and Versatile Design: LED lights are compact and can be easily integrated into various hydroponic setups, including vertical farming systems. Their versatility allows for more creative and space-efficient growing configurations (Nájera et al. 2022; Neo et al. 2022).

In conclusion, technological innovations such as automation, IoT integration, and advances in LED lighting are transforming hydroponic farming. These technologies enhance the precision, efficiency, and scalability of hydroponic systems, making them more viable and attractive for both small-scale and commercial growers. As technology continues to evolve, the potential for further advancements in hydroponics remains vast, promising even greater sustainability and productivity in the future of agriculture.

Table 2. The technological innovations/advances in Hydroponic system.