Liquid cultivation of tomato [Lycopersicon esculentum] plants by daily control of fertilizer application in which there are no N/P/K residues in the culture solution and the area of the leaf groups is used as an indicator

1) When N: 10 mg and P: 0.125 - 4 mg were applied daily to tomato plants using a culture solution containing Ca, Mg, S and K in more than the standard concentrations, each plant after harvesting time absorbed N and P to extremely lower concentrations when the N: P ratio was 10:1. When a culture solution containing Ca, Mg, S and K in more than the standard concentrations was applied, the amount of P applied was rate-determining to the growth of tomato when N/P was > 10, and the amount of N applied was rate-determining when it was <10. 2) When N: 10 mg and K: 0.75 - 24mg were applied daily to tomato plants using a culture solution containing more than the standard concentrations of Ca, Mg, S and P, individual plants after harvesting time absorbed N and K to extremely lower concentrations when the N: K ratio was 1:06. When a culture solution containing Ca, Mg, S and P in more than the standard concentrations was applied, the amount of K applied was rate-determining to the growth of tomato when N/K was > 1, and the amount of N applied was rate-determining when it was < 1. 3) When N: 10 mg and Ca: 0.1 - 3.2mg were applied daily to tomato plants using a culture solution containing Mg, S, K and P in more than the standard concentrations, individual plants after harvesting time showed symptoms of Ca deficiency, even though Ca was present in the culture solution. Moreover, the production of fruit and growth was abnormal and the growth of plants was not parallel to the amount of Ca applied. The lowest threshold value of Ca in the culture solution in which tomatoes could grow normally after harvesting time was different by season, being 20ppm during mild periods and 10ppm during cold periods, and the growth of tomato plants was considerably inhibited in the culture solution containing Ca in a concentration less than the threshold value. 4) When N: 10 mg and Mg: 0.15 - 4.8mg were applied daily to tomato plants using a culture solution containing Ca, S, K and P in more than the standard concentrations, individual plants showed symptoms of Mg deficiency and the growth of plants was not parallel to the amount of Mg applied, even though Mg was present in the solution. The lowest threshold value of Mg in a culture solution in which tomato plants could grow normally after harvesting time was different depending on the season, being 20 ppm during mild periods and 10 ppm during cold ones, and the growth of plants was inhibited considerably in a culture solution containing Mg less than the threshold value. When the concentration of Mg in a culture solution was more than 50 ppm, the absorption of Ca was inhibited, showing possible presence of the highest limit of concentration of Mg in a culture solution. 5) Competitive absorption of Ca and Mg by tomato plants in a culture solution containing N, P and K in extremely lower concentrations was examined. As a result, the absorption of Mg and K were hardly affected by the concentration of Ca. It was shown that the absorption of Ca, Mg and K were not competitive with one another, but that there was inhibition/interference action by Mg or K to Ca absorption. When tomato plants were cultured in a solution containing Mg in 20 or 40 ppm and N, P, and K in extremely lower concentrations and the EC value was elevated to 10 with CaCl2, no occurrence of shiri-gusare fruits (fruits rotten in the rear) was observed, even in mid-summer. It was recognized that the Ca deficiency of tomato plants by the increase of EC was caused by the inhibition of Ca absorption due to the increase of Mg or K in the culture solutions rather than by the inhibition of Ca absorption due to water stress. 6) When N: 9 mg and S: 0.34 - 18.9mg were applied daily to tomato plants after harvesting time under the condition that Ca/Mg and K/P were present in more than standard concentrations in the culture solution, individual plants showed symptoms of S deficiency in the plot where S was absorbed completely and also in the plot where S remained in the culture solution. The S deficiency and abnormal growth were observed to be gradually in inverse proportion to the amount of S applied, and the amount of S applied was not proportional to the yield of tomato fruit. The lowest threshold concentration of S in the culture solution enabling tomato plant to grow normally after harvesting time was about 40 ppm. When the concentration of S in a culture solution was lower than the threshold value, the growth of tomato plant was retarded considerably and inhibited. 7) The absorption characteristics of tomato plants for major fertilizer elements may be summarized as follows. N/P/K: Growth proportional to the amount applied is expectable and they are absorbable to extremely lower concentrations from the culture solution. S: Absorbable to extremely lower concentrations from the culture solution, but growth proportional to the amount applied is not expectable for a culture solution containing the element at less than the threshold value. Ca/Mg: Not absorbable to lower concentrations, and growth proportional to the amount applied is not expectable for a culture solution containing less than the threshold values of these elements. When small amounts of N, P and K were applied daily to individual plants, the growth was controlled by the element lacking most, and symptoms for N, P and K deficiency were scarcely observed. 8) The amounts of N, P and K were regulated on the basis of analyses of the culture solution 4 times at 7-day intervals from 30 days before the end of cultivation, and the regulated amounts were applied daily. Under the above conditions, the whole amount of N/P/K was absorbable from the culture solution wasted after the end of cultivation in the Application Method of Nitrogen Distributed in Small Portions (the NDSP Method), and scarce amounts of Ca/Mg/S remained in the culture solution. Moreover, liquid cultivation of tomato plants that is friendly to the environment with 100% fertilizing efficiency for N/P/K, equivalent to the NDSP Method, was attainable. 9) Yearly liquid-circulating cultivation of tomato plants without residual N/P/K in the culture solution can be accomplished by the following methods. CD Prepare Fertilizer C with Mg/Ca/S content in compliance with those in the fruit because normal growth of tomato plants is not attainable if the concentrations of these elements in the culture solution are less than the threshold values. In order to attain the lowest threshold value of each element, tomato seedlings are planted in cultivation cells containing Fertilizer C with EC values raised to 0.7 -1.0. (2) Prepare Fertilizer A in which the N/P/K/Mg/S elements are combined in compliance with the absorption ratio by tomato plants, utilizing the growth characteristics of tomato plants, which absorb the major elements of fertilizers in a definite ratio after harvesting time. Regulate the amount of Fertilizer A applied daily, making use of the area of the leaf groups in individual plants most suitable to photosynthesis as an indicator, and apply it daily in accordance with the Quantity-control Method. (3) Regulate the EC value of the culture solution with Ca Fertilizer B by the use of an EC meter and making use of the sugar degree (Brix) of the fruit as an indicator. (4) Regulate the pH of the culture solution to 5 - 6 once a day with Ca(OH)2 and H2SO4. 10) Liquid cultivation of tomato plants that is friendly to the environment, with 100% fertilizing efficiency for N/P/K and high productivity yielding 25 - 30t of good tomato fruits yearly, can be accomplished if 3500-4000 plants are planted per 10a to secure the number of fruits, if the area of the leaf groups in individual plants is kept at a level suitable to photosynthesis, and an EC value of 8 L of culture solution per individual plant is maintained at 1 - 3. Thus, there is no residual N/P/K in the culture solution (less than in tap water) from planting to the end of cultivation, and there is no drainage of N/P/K in incidence of overflow of the culture solution. Moreover, the concentrations of S and Mg in the culture solution are stable, excess accumulation of residues is not present, the major elements are applied daily without causing deficiency throughout the year, and analysis and exchange of the culture solution are not required throughout the year. The cultivation of tomato plants with a high sugar degree (Brix 8) is attainable if the EC value of the culture solution is altered with Ca fertilizer and the water stress of tomato plants is controlled.