2017 ASHS Annual Conference

The recycling operating system of waste nutrient solution (WNS) in view of closed hydroponic cultivation is important to reduce the cost of purchasing fertilizer and to preserve the natural environment by eliminating the unauthozied discharge of organic and inorganic nutrients. We therefore investigated the changes of inorganic compounds in WNS and tomato plant leaves, and the diversity of microorganisms in WNS to determine whether it is possible or not to recycle the WNS drained in hydroponic cultivation of tomatoes during spring cultivation. The change of EC in WNS was increased by 4.5 dS.m^-1 when tomato plants were grown until the 9^th fruiting node than the initial rate of 2.0 dS.m^-1 at the 2^nd ones. However, the pH of WNS was lowered to pH 5.9-6.1 at the 9^th and the 10^th fruiting node compare to pH 6.4-6.7 at the 2^nd and the 3^rd ones, respectively. The concentrations of nitrogen (NO₃-N), phosphorus (PO₄), potassium (K), calcium (Ca), magnesium (Mg) and boron (B) were similar in both WNS and initial nutrient solution (INS) during the 2^nd and the 3^rd fruiting stage, while their concentrations in WNS were higher than that of INS at the middle and late fruiting of tomato. The Fe content was also higher in INS than that of WNS from the beginning to the end of tomato growth. During the cultivation, the density of the microorganisms were 2.3 to 9.4 x 10⁶ cfu.ml^-1 in the WNS. Trichoderma, Penicillium and Pseudomonas spp. were isolated into dominant species and they have been found to be non-pathogenic fungi and bacteria. The content of total NO₃-N in the leaves was 4.01% level at the 2^nd fruiting node, but it was reduced by 2.75% at the 10^th ones. The phosphorus (PO₄) concentration in the analysis of the leaves was not difference from 2^nd fruiting node to 10^th ones, however the concentration of K and Ca were increased slightly during tomato growth. The content of Mg is 0.67 to 0.92% of the total. The results of these experiments showed that the reuse of WNS could be possible because of the high concentration of inorganic compounds and non-pathogenic microoganisms in the WNS.