||It has been suggested that this article be merged into Hydroponics. (Discuss) Proposed since November 2011.|
Organic hydroponics is a hydroponics culture system which is managed based on organic agriculture concepts. Most studies have focused on use of organic fertilizer. Conventional hydroponics cannot use organic fertilizer because organic compounds contained in hydroponic solution inhibit the growth of the crop roots, so it uses only inorganic fertilizer.
In this method of organic hydroponics, organic fertilizer is degraded into inorganic nutrients by microorganisms in the hydroponic solution via ammonification and nitrification. The microorganisms are cultured with a method of multiple parallel mineralization. The culture solution can be used as the hydroponic solution. Practical method of organic hydroponics is developed in National Agriculture and Food Research Organization (NARO), in Japan, in 2005.
History of organic hydroponics
Studies for establishing organic hydroponics have been conducted for a long time. Kennedy Space Center had studied organic hydroponics for crop production in space. It was necessary to develop the method to generate nitrate from organic fertilizer via ammonification and nitrification, because most of crops are nitrate-phylic but not ammonium-philic. It is easy to generate ammonium from organic fertilizer by saprophytic microorganisms. However it was difficult to degrade organic fertilizer to nitrate efficiently because the growth of nitrifying bacteria, such as the obligate chemolithoautotrophs Nitrosomonas spp. and Nitrospira spp., is particularly inhibited by the presence of organic compounds (Jensen 1950; Quastel and Scholefield 1951; Rittenberg 1969; Smith and Hoare 1977; Krummel and Harms 1982; Takahashi et al. 1992; Stutte 1996; Xu et al. 2000; Tomiyama et al. 2001).
Shinohara  invented the method to efficiently generate nitrate from in water. The method, multiple parallel mineralization, consists of three manipulations: small inoculation of soil microorganisms, addition of small amounts of organic fertilizer, and aeration. The mineralized solution can be used as the hydroponic solution and organic fertilizer can be added in the solution during cultivation. This is the first practical organic hydroponics technique that organic fertilizer can be added directly during cultivation.
Farajollahzade et al., introduced a method in which soil remained as the source of nutrients and the nitrogen was supplied by a in-line tank containing nitrogen-fixing bacteria. This method could be considered as a variation of soil culture in which the plant and soil are connected by cycling liquid. By use of organic soil as the source of nutrients, they believe that it could be considered within the definition of organic agriculture.
- NOTE: In the USA there is a great deal of debate within the organic community regarding hydroponically grown crops being certified as organic. Currently the National Organic Program (NOP) has not offered any guidance in this area and has ignored the recommendations of its own advisory board, the National Organic Standards Board (NOSB), which decided that hydroponic growing should not be allowed organic certification in the USA. Most other countries, including Canada and Mexico do not permit hydroponic crops to be labeled organic.
(1) Missing reference
(2) C.L. Mackowiaka, b, J.L. Garlanda, b, R.F. Strayera, b, B.W. Fingera, b, R.M. Wheeler (1996) Comparison of aerobically-treated and untreated crop residue as a source of recycled nutrients in a recirculating hydroponic system. Adv. Space Res. 18, 281-287
(3) M Shinohara, C Aoyama, K Fujiwara, A Watanabe, H Ohmori, Y Uehara & Masao Takano (2011) Microbial mineralization of organic nitrogen into nitrate to allow the use of organic fertilizer in hydroponics. Soil Sci. Plant Nutr. 57, 190-203
(4) Z Farajollahzadeh, E Hadavi, and A. Khandan-Mirkohi (2014)Introducing a potentially organic hydroponics system in production of pot gerbera flowers. Acta Hort. (ISHS) 1037:1075-1082, http://www.actahort.org/books/1037/1037_142.htm