2006 Volume 5 Issue 1 Pages 39-44
The present study aimed to stabilize high tomato fruit yields with high soluble solids on long-term hydroponic cultivation using an organic substrate culture. The water holding properties of an organic substrate (made with cedar bark or coconut husk and bark compost) were investigated. Use of an irrigation control system based on solar radiation, and the effects of the irrigation interval on fruit yield and quality were also investigated. In the case of substrates drained after water had been absorbed, the volumetric water content decreased sharply in organic substrates compared to that in rockwool. The volumetric water content was higher in organic substrates compared to that in rockwool at pF2.7. The amount of leaf area changed only slightly after removing leaves under the second truss; a positive correlation was seen between total integrated solar radiation and the evapotranspiration rate in long-term tomato cultivation. Irrigation treatments were a function of the total integrated solar radiation with three thresholds (MJ·m−2); 1.71, 1.93, and 2.14 (1.50, 1.71, 1.93 before removing leaves under the second truss). Nutrient solution was supplied at a rate of 100 mL per plant during each irrigation. The marketable yield decreased and the soluble solids content increased as the thresholds increased. However, the yield of fruits with highly soluble solids (Brix 8% or more) was highest when irrigation thresholds were 1.93 MJ·m−2 (1.71 before removing leaves under the second truss).
