Effects of different application methods of controlled-release fertilizers on capillary wick culture of tomato

Abstract

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 ["tankfertilization" (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, springLsummer and fallLwinter. 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 ofNH4-N/NO3-N was thought to be lower inMFthan 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 capillarywick irrigation system for tomato production is possible by promoting nitrification in the water reserve tank.