A Study on a Simple Passive Hydroponic System for Melon Production
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J. Japan. Soc. Hort. Sci. 64(4) : 839-844. 1996. A Study on a Simple Passive Hydroponic System for Melon Production Hideo Ikeda*, Keiko Tagami and Naoya Fukuda Institute of Agriculture and Forestry, University of Tsukuba, Tsukuba, Ibaraki 305 Summary Melon plants were grown from spring to summer (crop 1) and summer to autumn (crop 2) by a passive hydroponic system which was laid below the ground surface, so that plants can be grown and harvested without management of the nutrient solution. The effects of the initial concentration of nutrient solution on the growth of plants, yield and quality of fruits, and absorption of water and minerals were investigated while using this system. The concentrations of the nutrient solution had varied effects on plant growth and fruit yield of melon, depending on the growing season. The marketable fruits were har- vested from plants grown in the higher concentration plots in crop 1 and in all plots in crop 2. The temperature of the root zone was relatively low and fluctuated little even in the summer (crop 1), because the growing system, that is, solution reservoir was laid be- low the ground surface. Thus, it was concluded that this passive hydroponic system may be an useful and practical production technique for melons. However, more trails need to be conducted to adjust the nutrient solution for practical use. roots can absorb oxygen directly from the air. Introduction Electric pumps are not necessary, but before Many kinds of soilless culture techniques for planting, the nutrient solution required for one the production of vegetable crops have been estab- crop must be prepared in an underground reser- lished in Japan (Ikeda, 1994, 1995), as in other voir. Then after planting, such care as control of countries (Adams, 1990; Cooper, 1979; Hitchon et pH, electric conductivity (EC) and mineral com- al., 1990; Imai, 1987; Koontz et al., 1990; Kratky position of the solution, aeration, renewal of the et al., 1988). Almost every system use an electric solution, etc. is not required until harvest. pump for supplying the nutrient solution and/or However, for this hydroponic system, the proper air to plants. In most hydroponic systems, the pH, growing conditions for each crop, that is, optimum concentration, elemental composition, aeration and nutrient concentration and composition and pH of flow rate of the nutrient solution have to be con- the nutrient solution, have not yet been studied. trolled during growth periods. Those management In this experiment, melon plants were grown by practices are, however, fairly difficult and trouble- passive hydroponics; the effects of the initial con- some for growers to maintain. centration of the nutrient solution on the growth Recently, a new concept for a hydroponic sys- of plants, yield and quality of fruit, and absorption tem called "Passive hydroponics" was adapted by of water and minerals by the plants were investi- Ono (1988) in Japan. This growing system was gated. originally started in the U.S.A. as a Skaife Truck Materials and Methods Farm (Jones, 1983). In this system, once plants absorb nutrient solution, the water surface de- From our preliminary experiment, our passive creases, and naked roots with fine root hairs de- hydroponic system illustrated in Fig. 1, was esti- velop in the air above the water surface. Thus, the mated to require about 100 liter of nutrient solu- tion for one crop of melons even during the hot Received for publication 26 December 1994. * Present address; College of Agriculture season. This volume of nutrient solution was pre- , University of Osaka Prefecture, Sakai, Osaka 593. pared and stored in an underground 120 liter 839 840 H. Ikeda, K. Tagami and N. Fukuda plastic bucket as a reservoir. Three initial concen- tic cylinders (14 cm in diam. and 60 cm long) fil- trations of nutrient solution were: 1/3, 1 (full) and led with fresh rice hulls. The perforations allowed 3 times strength of the Japanese standard nutrient roots to grow into the external nutrient solution. solution (Enshi-shohou). The composition of the Melon plants were transplanted and grown from full strength solution in me• liter-1 was NO3-N, 16; March 5 and harvested on June 26 (crop 1) and NH4-N, 1.3; P, 4; K, 8; Ca, 8; and Mg, 4. Iron was from August 20 to November 19 (crop 2). Custom- added as an iron salt of EDTA (Ethylene- ary to a Japanese cultural practice, each plant bore diaminetetraacetic acid) to produce a concentration only one fruit. of 3 ppm. The microelements were added accord- During growth period, pH and EC values of the ing to Hoagland and Arnon (1950), and the pH of solutions were checked at regular intervals. At the the solution adjusted to 5.5. The bucket was co- end of the experiment, fresh and dry weights of vered with a reflective film to prevent algae leaves, stems and roots, and sizes and sugar con- formation and to keep the moisture content high. tents of fruits were determined. At the start and The experiment had five replications. end of the experiments, nutrient solutions were Seedlings of melon, cv. 'Amusu', grown on rock- sampled and analyzed by the following methods: wool cubes were transplanted into perforated plas- NO3-N; by ultraviolet spectrophotometry (Norman and Stucki, 1981), P; by ammonium-vanadate- molybdate-method on a spectrophotometer, K, Ca and Mg; by atomic absorption. Results Although the air temperature was very high and fluctuated during the crop 1 period, root zone temperature was low and rather stable in this sys- tem (Fig. 2). Leaves of melon plants grown in the 1/3 strength nutrient solution became a light green to yellow 3 to 4 weeks after transplanting in crop 1 but in 1 week in crop 2. Leaves of plants grown in the 3 times strength solution remained a dark green. The total dry weight of plants in crops 1 and 2 was the highest in the full strength solution (Table Fig. 1. The passive hydroponic system used in the 1). In crop 1, the leaf dry weight of plants grown experiment. Fig. 2. Air and root zone temperature during the experiments. J. Japan. Soc. Hort. Sci. 64 (4) : 839-844. 1996. 841 in the full strength solution was almost double (Fig. 4), whereas in the full and 3 times strength that of plants grown in the 1/3 strength solution solutions, EC increased after about 5 weeks of and equivalent to 60 % of the total dry weight. treatment. The former became 6 mS¥cm-1 while The amount of nutrient solution absorbed by a the latter became about 12 mS¥cm-1 by the end of plant ranged from 66 to 92 liter in crop 1 and 64 the experiment. to 84 liter in crop 2; plants with the higher dry Analytical data of the solution at the end of the weight absorbed more solution. experiment showed that the concentration of all In crop 1, the fresh weight of fruit was the mineral elemetns in the 1/3 strength solution de- lowest in the full strength solution and the highest creased compared with the initial one (Table 3), in the 3 times strength solution (Table 2). Melons especially, NO3-N which decreased to 4 to 5 ppm. had the highest sugar content and the best apper- However, concentration of mineral elements in the ance in the 3 times strength solution. In crop 2, full and 3 times strength solutions increased by however, fruit size did not differ among the treat- the end of the experiment. ments and the quality was equally high. Discussion The pH of the solution fluctuated between 4.5 and 6.5 in crops 1 (Fig. 3); in crop 2, however, pH In general, hydroponics evolved as a high tech- of the 1/3 strength solution sharply decreased to nology plant production system until now. The below 4.0 after 7 weeks of treatment. EC of the main advantages of hydroponics over all other 1/3 strength solution remained almost constant types of soil culture are: 1) more efficient nutrient Table 1. Effects of initial concentration of the nutrient solution on growth of melon plants and the amount of nutrient solution absorbed by a plant. Table 2. Effects of initial concentration of the nutrient solution on size, fresh weight and sugar content of melon fruits. 842 H. Ikeda, K. Tagami and N. Fukuda Fig. 3. The changes in pH of the nutrient solution during Fig. 4. Changes in the electric conductivity of the nut- the experiments as affected by the initial concentra- rient solution during the experiments as affected by tions. the initial concentrations. Table 3. Mineral composition of the nutrient solution at the start and end of the experi- ment. (me¥liter-1) regulation, 2) availability in regions of the world The nutrient film technique (NFT), which is a very having nonarable land, 3) efficient use of water simple water culture system, was originally de- and fertilizers, 4) ease and low cost of sterilization veloped by Sholto Douglas in India in 1973 for of the medium, and 5) higher density planting, the purpose of providing a cheap and simple leading to increased yields per acre (Resh, 1993). means for the local people to grow their own fresh J. Japan. Soc. Hort. Sci. 64(4) : 839-844. 1996. 843 , vegetables. NFT, however, needs the solution flow 30 cm and deeper from soil surface in the green- by an electric pump. If a simple passive hydropo- house is stable and maintained at 16° to 17 °C all nic system were developed, it should become a year round (Sasaki, 1987).