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Application of controlled-release fertilizer (CRF) to root-proof capillary-wick irrigation systems (a type of subirrigation method) has both economic and environmental benefits because it does not require any equipment for fertigation and minimizes water leaching. In this study, we compared three CRF fertilization methods: 1) mixed with the substrate completely [“mixed-fertilization” (MF)]; 2) packed in bags and placed on the wick [“packed bag-fertilization” (PF)]; and 3) supplied in the water reserve tank [“tank-fertilization” (TF)] in tomato cultivation using the root-proof capillary-wick irrigation system. We also refined the TF method to simplify and reduce labor requirements for fertilization of CRF and reuse of substrate. Fruit yield was lower in PF and TF than in MF because of high incidence of blossom-end rot (BER) in PF and TF during both cultivation periods, spring−summer and fall−winter. However, promotion of nitrification in TF by supplying nitrogen through the addition of bark compost and aeration of the water reserve tank increased fruit yield to the same level as that observed in MF as a result of a decrease in BER incidence. Nutrient residue in the substrate was lower in TF than in MF. On the basis of the analysis of nitrogen concentration in xylem exudates, the uptake ratio of NH₄-N/NO₃-N was thought to be lower in MF than in PF and TF. The high NH₄-N uptake in PF and TF could be the cause of calcium (Ca) deficiency and increased incidence of BER. Thus, the use of “tank fertilization” of CRF in the root-proof capillary-wick irrigation system for tomato production is possible by promoting nitrification in the water reserve tank.

Application of controlled-release fertilizer (CRF) to a root-proof capillary wick irrigation system (a type of subirrigation method) has both economical and environmental benefits, because it does not require any equipment for fertigation and minimizes water leaching. In this study, we examined the effects of CRF and liquid fertilizer (LF), a conventional fertigation method, on fruit production and nutrient uptake and transport in forcing tomato cultures for harvesting 15 trusses per plant from October to June. No significant difference was noted in marketable fruit yield between CRF- and LF-treated plants. The quantity of nutrient uptake per plant and per fruit yield was lower with CRF than with LF, indicating that nutrients were used more efficiently for fruit production in plants grown with CRF. Analysis of the volume and mineral concentrations of xylem exudates indicated that the amount of nutrients absorbed was greater with LF than with CRF, particularly after the tenth truss was harvested. Mineral concentrations in the substrate solution of CRF-treated plants were initially higher than those in the substrate solution of LF-treated plants but extremely low after the second truss was harvested, whereas mineral concentrations in the xylem exudates were similar in CRF and LF plants until the eighth truss was harvested. Thus, the difference in mineral concentrations between the xylem exudates and substrate solution was much larger in the case of CRF than in the case of LF, indicating that the plants absorbed the bulk of nutrients immediately after their release from the CRF surface. Therefore, CRF is suitable in this system, because it combines high fruit production with high nutrient utilization efficiency.