Organic hydroponics uses 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 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 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 (1) 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.