ACADEMIA Letters Organic nutrient solution for hydroponic system H. F. Lakma Upendri Brintha Karunarathna Organic nutrient solution for hydroponic system H. F. L. Upendri and Brintha Karunarathna Department of Crop Science, Faculty of Agriculture, Eastern University, Sri Lanka Abstract Hydroponics is a method of crop production that has been successfully used soilless growing media for the growth of vegetables, flowers, herbs and other crops. It uses a nutrient solution and generally controlled environmental conditions which makes it more energy intensive and more productive than conventional agriculture. Hydroponic systems, a popular technique of highly resource and space efficient form of cultivation, already contribute extensively to global food production. High usage of chemical or inorganic fertilizers in agricultural sectors including hydroponics has raised concern towards healthy living environment. An environmental friendly agricultural system with organic fertilizer is used to reduce the use of chemical fertilizers, thus producing healthy agricultural products for consumption. Organic hydroponics is a system that is organized based on organic agriculture concept. Use of liquid organic fertilizers produced from agricultural residues and industrial wastes are increasingly popular in organic hydroponic system. The object of this review aimed to give an effective possibilities to use organic agriculture in hydroponic using liquid organic fertilizers based on different organic products. Keywords: Hydroponics, nutrients, organic, soilless, liquid Introduction The word ’Hydroponics’ was introduced by Dr. W.F. Gericke in 1936 to define the edible and ornamental plants cultivated in a solution of water and dissolved nutrients. In definition hydroponics derives from two Greek words ‘hydro’ and ‘ponics’ which means water and working respectively. Hydroponics is a method of growing plants using mineral nutrient soAcademia Letters, July 2021 ©2021 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: H. F. Lakma Upendri, lakmaupendri19931109@gmail.com Citation: Upendri, H.F.L., Karunarathna, B. (2021). Organic nutrient solution for hydroponic system. Academia Letters, Article 1893. https://doi.org/10.20935/AL1893. 1 lutions without soil (Sardare and Admane, 2013). The solution supply plant nutrients with dissolved fertilizers in water and nutrients are fed directly to the roots. This system is a type of soilless culture but it is a wider area than hydroponics. Hydroponics is a soilless culture but not all soilless cultures are hydroponics. The nutrient solution is one of the most important factor determining the crop yield and quality among factors affecting hydroponic production systems. Hydroponics uses less than 1/10th - 1/5th of the water compared to soil cultivation. The essential nutrients are supplied to hydroponic plants in the form of nutrient solution. Hydroponics is an excellent technique for the cultivation of vegetable crops and other plants. The conventional hydroponic systems commonly utilize only inorganic fertilizers, but using high concentrations of chemical fertilizer negatively effect on consumers due to the accumulation of toxic chemicals in vegetables. Due to the use of synthetic fertilizers, nitrates may accumulate in vegetable leaves such as lettuce (Gent, 2003). The accumulation of higher levels of nitrate in plants are detrimental in both human health and plant growth (Anjana and Iqbal, 2007; Ikemoto et al., 2002; Ishiwata et al., 2002). Therefore, the use of liquid organic fertilizer as a replacement or supplement to chemical fertilizer is an important feature for hydroponic planting. Organic hydroponics Incorporating organic nutrient solution for hydroponics is a new approach in spite of application of organic and inorganic nutrients on soil (Liang et al., 2014). The emergence of organic hydroponics came in the 1990s. As stated by Hadad and Anderson (2004), farmers prefer to use organic fertilizers for vegetable production. So that hydroponic systems developed in various forms and types. Organic hydroponics is a hydroponics culture system based on organic agriculture models which does not use synthetic inputs such as fertilizers or pesticides. Organic and conventional hydroponic systems practice same technique of supplying nutrients in solution for growth of plants. Liquid organic fertilizers can be used as a substitute for nutrients in hydroponics which is free from chemical because it derives from organic materials that are safe for health. Nutrient solutions are derivatives of plant and animal substances or naturally extracted constituents (Atkin and Nichols, 2003) or a solution of decomposing organic matter from plant residues, agro-industrial waste, animal manure, and human waste. The liquid organic fertilizers are produced by a simple fermentation processes using organic wastes as carbon substrates. Liquid organic fertilizers consist of essential plant nutrients and beneficial microorganisms, which recycle or degrade the organic substrate. The nutrient solution will comprise phytohormones, organic acids and plant growth promoters after fermentation process in order to influence on plant growth and development in organic hydroponics. Diseases and insect are a main challenge in hydroponic production systems. Different Academia Letters, July 2021 ©2021 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: H. F. Lakma Upendri, lakmaupendri19931109@gmail.com Citation: Upendri, H.F.L., Karunarathna, B. (2021). Organic nutrient solution for hydroponic system. Academia Letters, Article 1893. https://doi.org/10.20935/AL1893. 2 methods are used to control plant pathogens such as physical, natural chemicals, biological controls, biofertilizers, bioremediators and integrated pest management in organic hydroponics avoiding synthetic pesticides. The outcome will be a hydroponic system, which will be sustainable, easy to manage, cost-effective and environmentally friendly system. Nutrient solutions There are a number of promising sources for liquid organic fertilizer used in organic hydroponics. Liquid organic fertilizers produced from agricultural residues and industrial wastes and various sources are becoming increasingly popular. Waste nutrient solution can be used as an alternate resource for crop cultivation under hydroponic system (Choi et al., 2011). Confirming that Mavrogianopoulos et al. (2002) used wastewater for hydroponics and tested the growth and biomass production of giant reed (Arundo donax L.) for sewage effluents without detrimental or toxic effect. Susnawati et al. (2015) study also showed that greywater can be used as hydroponic media solution in water spinach and lettuce. The use of liquid organic fertilizer as a replacement or supplement to chemical fertilizer is a better solution for hydroponic planting. Fish-based soluble fertilizer and corn steep liquor, which are byproducts of food production or treated food waste were used as liquid fertilizer in hydroponics (Aoyama et al., 2014). Similarly, different sources of liquid organic waste byproducts, such as compost, biogas effluent, soluble fish waste, or corn steep liquor have been utilized (Shinohara et al., 2011). Further some studies have reported the possibility of using rapeseed oil cake, corn oil cake, fish meal, dried brewer’s yeast, fermented tomato foliage, sea Academia Letters, July 2021 ©2021 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: H. F. Lakma Upendri, lakmaupendri19931109@gmail.com Citation: Upendri, H.F.L., Karunarathna, B. (2021). Organic nutrient solution for hydroponic system. Academia Letters, Article 1893. https://doi.org/10.20935/AL1893. 3 weed, and vermicaste derived solutions in hydroponic systems (Kano et al., 2021). Moreover, study in Thailand evaluated different ratios of waste molasses, distillery slop, and sugarcane leaves which are carbon rich wastes from agro-industry factories, provide a source of organic matter have the potential to be used for liquid organic fertilizer production and observed comparable growth rates those of chemical fertilizer in green cos lettuce (Lactuca sativa var. longifolia) (Phibunwatthanawong and Riddech, 2019). Nasir et al. (2012) tested using of bio-slurry, byproduct of an anaerobic fermentation of organic matter from biogas reactors as a nutrient source for growing hydroponic plants. Further, Cheng et al. 2004 reported liquid effluent from anaerobic digestion (digestate) also has the potential for use as a fertilizer in hydroponic cultures. According to the literature, Moringa leaves (Moringa oliefera) and wastewater from rice washing have high mineral and vitamin content can be used as organic liquid fertilizer in hydroponics to the growth of pakcoy plant (Brassica rapa L. spp. Chinensis (L.) in Indonesia (Sari et al., 2020). Liquid organic fertilizer from bamboo shoots is also an alternative substitute for chemical fertilizers in the planting of cayenne pepper (Capsicum frutescens L.) hydroponically (Saputri et al., 2021). Vermicompost leachate, or worm compost tea which is a highly nutritious fertilizer already in liquid form can be easily used in hydroponic systems if the food and animal waste used in its production are of high quality. Bidabadi et al. (2016) reported an efficient results using vermicompost derived liquids as a nutrient supplement in stevia culture via a suitable hydroponic system. Umapriya et al. (2019) also designed a hydroponics setup with natural means such as vermicompost extract, vegetable waste extract, Panchakavya and cattle shed soil extract for the cultivation of medicinal herbs. Tikasz et al. (2019) experimented on effect of using animal wastes such as chicken, cow, and turkey manure extracts on yield of lettuce and kale yield in hydroponics. Liquid organic fertilizers used in hydroponic systems are typically concentrated solutions of organic nutrients that are diluted for use. Moreover, most of the nutrients in organic sources, such as waste material from the agricultural and industrial effluent, are not in ionic forms and, hence, are not directly available for plants. Also most of the organic fertilizers are generally insoluble in water, and nutrients are not readily available for plants as they are converted to soluble form by microorganisms. Hence a solubilization step is needed to break down organic matter and mobilize nutrients for optimizing the utilization of organic waste for hydroponic plant growth. Furthermore, the direct use of organic fertilizers in hydroponic systems may inhibit plant growth and can be toxic to plants by accumulation of minerals, organic acid and plant exudates (Foucard and Tocqueville, 2019). Therefore, it is essential to regular checking of the pH and Academia Letters, July 2021 ©2021 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: H. F. Lakma Upendri, lakmaupendri19931109@gmail.com Citation: Upendri, H.F.L., Karunarathna, B. (2021). Organic nutrient solution for hydroponic system. Academia Letters, Article 1893. https://doi.org/10.20935/AL1893. 4 concentration of the solution in order to prevent it becoming phytotoxic (Jijakli, 2018). Constraints Using liquid organic fertilizers in hydroponics limited due to rapid pH fluctuation, difficulty of organic certification and excessive or unwanted constituents in organic nutrient sources (Williams and Nelson, 2016). The organic certification of hydroponics have been a heavily debated theme belongs to organic production in the agriculture industry. Further, based on the production system and level of automation, it requires high investment, technical knowledge and experience which could prevent its use by smallholders (Savvas, 2003; Phibunwatthanawong and Riddech, 2019). Also, different types of organic fertilizers, crops, and hydroponic systems perform differently. Therefore, it is difficult to disclose efficacy of organic fertilizers in hydroponics. Conclusion The aim of this review was to identify possibility of using organic residues and wastes from different sources to produce liquid organic fertilizer and to evaluate the effectiveness of the fertilizer on the promotion of plant growth in a hydroponic system. It can be concluded that organic hydroponics based on this method is a practical solution using variety of organic sources as liquid fertilizer. Plants produced from organic hydroponic system are Academia Letters, July 2021 ©2021 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: H. F. Lakma Upendri, lakmaupendri19931109@gmail.com Citation: Upendri, H.F.L., Karunarathna, B. (2021). Organic nutrient solution for hydroponic system. Academia Letters, Article 1893. https://doi.org/10.20935/AL1893. 5 safe, healthy and environmentally friendly. References Andrian, D., Tantawi, A.R. and Rahman, A. (2019). 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