2017 ASHS Annual Conference

It is important to develop the recycling system of waste nutrient solution (WNS) in view of closed hydroponic cultivation of tomatoes, because many farmers have grown tomatoes with hydroponics and released a lot of WNS once used to the surrounding natural environment without permission. So we investigated the changes of inorganic compounds to examine the possibility of recycling of WNS, which is a Yamazaki nutrient solution drained during hydroponic cultivation of tomato using coir-perlite from March 18^th to June 28^th. The EC of WNS was increased by from 2.0 to 3.0 dS.m^-1 when tomatoes were grown. The pH of WNS was low as 5.5-5.8 level until mid-April, and maintained pH 6.1-6.4 level after the end of April. The concentrations of NO₃-N, PO₄ and K were similar in both WNS and initial nutrient solution (INS) during the early growth stage, while their concentration of WNS were higher than that of INS at the middle and late growth of tomato. The concentrations of Ca and Mg were no significant difference between INS and WNS until mid-April. But the concentrations of Ca and Mg in WNS were increased by 1.3-1.5 times than that of INS after the end of April. The Boron content was higher in INS by the end of March, but it was increased by 1.5 times in WNS than INS. The Fe content was also higher in INS than WNS from the beginning to the end of growth. In general, inorganic compound concentration in INS and WNS were no difference at the seedling period when absorption of nutrients is low. But that in WNS was higher than INS because evaporation loss of big plant increased. Although these results provided a lot of information about the changes of inorganic compounds in INS and WNS as one of the recycling nutrient solution for hydroponic cultivation of tomato, further studies for the availability of waste nutrients in plant vegetative and reproductive growth are required in the near future.