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Hydroponics is a method for growing crops without the use of soil, and with nutrients added to the irrigation water (so called fertigation) (Figure 1). The main differences between traditional in-ground growing techniques and soil-less techniques concern the relative use of water and fertilizer, and overall productivity. Soil-less agriculture is also typically less labour-intensive, supports monocultures better than in-ground agriculture, and can be used on non-arable land (Somerville et al. 2014c).
Figure 1: Classification of soil-less cultures according to the use of substrate or growing medium. The main role of substrate (if used at all) is to act as a support for the plants, and to provide moisture and aeration
Hydroponics allows the farmer to monitor, maintain and adjust the growing conditions of the plants, ensuring optimal real-time nutrient balances, water delivery, pH and temperature. In addition, there is no competition from weeds, and the plants benefit from higher control of pests and diseases. It is said that a plant grown using hydroponics uses 90% less water than would be used to grow the same plant in soil (Somerville et al. 2014c). In hydroponics the water used is the minimum needed for plant growth, while in-ground agriculture loses water through evaporation from the surface, percolation into the subsoil, runoff, and weed growth. Hydroponics therefore offers great potential for crop production in areas where water is scarce or expensive. Since the nutrients necessary for plant growth are in a solution that is delivered directly to the roots, the solution can be tailored to the plant’s needs at a particular growth stage. With in-ground agriculture, on the other hand, farmers cannot fully control the delivery of nutrients to the plants because of the complex processes occurring in the soil, and some fertilizer may be lost to runoff, which not only decreases efficiency, but also causes environmental concerns. Because hydroponically grown plants dip their roots directly into the nutrient solution, they obtain what they need much more easily than plants grown in soil, so they usually have smaller root systems and can divert more energy into leaf and stem growth. As a result, hydroponic culture can achieve between 5 and 25% higher yields than soil-based culture (Somerville et al. 2014c).
However, there are also some limitations to hydroponic systems. The main problem is the high initial setup cost. They are also vulnerable to power outages, as the electrical-driven devices in the systems cannot supply the nutrient solution without power. In addition, when phytopathogens (microorganisms such as Verticillium, Pythium, and Fusarium) contaminate solutions or crops, waterborne diseases can rapidly spread throughout the entire system. Hydroponic system operators need specialized skills and knowledge to produce high yields of crops; they must learn the proper amounts of nutrients and lighting, manage complex nutritional problems, maintain pest control, and prevent the formation of biofilms in the water tubing system. Finally, although nutrient-rich hydroponic solutions and plastic materials can be reused, hydroponic systems still generate a large amount of waste that can have negative impacts on the environment (Lee & Lee 2015).
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