Chapter I.
Tomatoes are classified as common or cherry type. Common tomatoes are classified as asian or european type by fruit skin color. Long-term cultivation requires sustained vigorous growth, and european type are selected instead of the asian, which is not easy to maintain for a long time, European types are known to have a different water and nutrient management compared to the asian or cherry types previously grown. This study was carried out to acquire basic data for long-term soilless culture by investigating the water and inorganic ion uptake according to tomato cultivars and EC of nutrient solution.
The influence of different EC level (1.0, 2.0, 3.0 and 4.0 dS·m-1) of hydroponic nutrient solution on water and inorganic ion uptake of three tomato cultivars, european type (cv, Daphnis), asian type (cv. Super dotaerang) and cherry type (cv. Minichal), were investigated. Tomato plants cultivated using the deep flow technique (DFT).
The higher the EC of the nutrient solution, the less water uptake.
The difference in water uptake of the three cultivars was not clear, but in the second survey, the ''Daphnis'' did not show a significant decrease in water uptake higher than EC 2.0 dS·m-1, on the other hand, ''Super dotaerang'' was very low in water uptake due to water absorption trouble in high EC of nutrient solution. At a low EC of nutrient solution, NO3-N, P, and K were absorbed higher than supplied concentration and at a high EC, the concentration of the remaining solution was much higher than the initial concentration, since it was absorbed by 50% or less compared with the initial concentration. ''Daphnis'' showed high absorption at low concentration and low absorption at high concentration. ''Daphnis'' was a cultivars that effectively utilized nutrients under nutrient stress conditions. However, ''Daphnis'' was the most severe symptom caused by excessive nutrients. At high EC of nutrient solution, leaf area and fresh weight decreased at first, and later all growth factors (plant height, leaf number, leaf area, fresh weight) were poor.
Chapter II.
1. Effect of EC level of irrigation solution on tomato growth and inorganic ions of root zone
In hydroponics, the nutrient solution is supplied considering the water and nutrient uptake characteristics of crops. However, as the ionic uptake characteristics are changed as a result of the weather conditions or the growth response of the crops, the root zone can not be maintained in optimal condition. In addition, the coir substrate has been used mainly for the tomato cultivation in place of the inorganic substrate, there are few studies on long-term cultivation using coir substrate. Therefore, this study was conducted to investigate the effect of EC level of irrigation solution on tomato growth and inorganic ions of root zone in soilless culture using coir. Coir substrate mixed with 5: 5 chip and dust was used. EC level of irrigation solution was 1.0, 1.5, 2.0, and 3.0 dS·m-1.
At the initial stage, NO3-N, P, Ca and Mg in the drainage were lower than the irrigation level at 1.0 and 1.5 dS·m-1. However, EC 2.0 dS·m-1 or higher, all the ions except P were highly concentrated in the drainage. The average fruit weight was not significantly different between 1.0 and 1.5 dS·m-1 until 3th cluster, but from the next cluster, the higher the EC level, the smaller the weight. The number of fruit to 5th cluster was the highest at 1.5dS·m-1, but the yield was higher at 1.0dS·m-1. The yield of high EC level treatment decreased with the later cultivation. Magnesium deficiency symptoms were observed in 18 - 25 nodes. This symptom was more severe in high EC level treatments. In the upper cluster where this symptom appeared, fruit setting and yield decreased. At the early stage of growth, BER occurred only in EC 3.0 dS·m-1, but increased in all treatments with increasing irradiation. The incidence rate of EC 3.0 dS·m-1 was higher than that of the lower EC level treatment.
2. Effect of irrigation volume on tomato growth and inorganic ions of root zone
In hydroponics, the accumulation of inorganic ions in the root zone are closely related to the irrigation volume. Therefore, the effects of irrigation volume on the growth and yield are very signigicant. This study was conducted to investigate the effect of irrigation volume on tomato growth and inorganic ions of root zone in soilless culture using coir substrate. The irrigation volume was adjusted 4 levels based on the integrated solar radiation. Set value of integrated solar radiation was changed according to the growing season.
The drainage rate was calculated by daily amount of irrigation and drainage. The monthly average irrigation volume and the drainage rate were calculated. The higher irrigation volume, drainage ratio and water absorption tended to increase. But, high of irrigation volume decreased water absorption in February and March compared with medium high, and fruit setting of 12 - 15th cluster and yield was low. The rate of drainage was selected from 20 to 30%, and 120 to 140 J/cm2 in January, 100 to 120 J/cm2 in February, 80 to 100 J/cm2 in March and 70 to 90 J/cm2 in April and 60 to 75 J/cm2 in May. The higher irrigation volume, higher the drainage rate, which could prevent the accumulation of nutrients. However, due to the characteristics of the coir substrate that adsorbing ions, the EC of the root zone was significantly higher when the drainage rate was 20-30%. Concentrations of ions in the draining water showed periodic patterns of change reflecting crop demand and seasonal environmental changes. Concentrations of P and K were sometimes lowered in the drainage concentration than irrigation regardless of the treatment. Mg and S were the most accumulated ions even in the case of high irrigation volume. At low radiation season, there was no difference in the ion concentration of the drainage according to the irrigation volume, at high radiation season, the lower irrigation volume was higher the inorganic ion in the drainage. After March, it was difficult to prevent the rise in the EC of the drainage by only adjusting irrigation volume, so it was necessary to lower the EC of irrigation solution to prevent the accumulation of nutrients in the root zone.
3. Effect of K and S strength in the irrigation solution on tomato growth and inorganic ions of root zone
In tomato long-term soilless culture, Mg deficiency often occurs because fruits of several clusters grow simultaneously. We hypothesized that the cause of this might be due to the suppression of Mg absorption while competing with K, which is relatively easy to absorb. In the nutrient solution composition, the anion should be controlled at the same rate for controlling the cation. S, which is easily accumulated in the root zone due to low uptake rate, was selected as the target anion. So, using K2SO4 fertilizer that can control these two ions at the same time. The effect of reducing the ratio of ions in the irrigation solution was examined.Using the tomato nutrient solution of PBG of Netherlands. Treatments with K and S ratios of 10%, 20%, and 45% reduced at standard and standard concentrations, respectively.
Since the substrate was washed just before the experiment, the inorganic ions of the drainage were lower than the experiment 2. Except for K and S, which had different composition ratios in culture, the other ions did not show the difference of ions in the drainage. The contents of K in the leaf were high and Mg and Ca was low with high K and S ratio. The total yields of all treatments with reduced K and S tend to be higher than those with standard treatments. The yields of 0.8 strength K and S higher than those of standard treatments were 8.6% higher than those of standard. The soluble solids was the highest in the 0.55 strength up to 4th cluster, and 0.8 strength higher from the next cluster.