Development of Closed, Energy-saving Hydroponics for Sloping Land

Transcription

1 Development of Closed, Energy-saving Hydroponics for Sloping Land T. Higashide, Y. Kasahara, T. Ibuki and O. Sumikawa National Agricultural Center for Western region 2575 Ikano, Zentsuji, Kagawa, Japan Keywords: hillside field, tomato, drip irrigation, flow rate, outflow, water pressure Abstract In sloping areas in Japan, tomatoes are produced under rain shelters in the summer. However, two serious problems affect tomato production in these areas. One is that the soil continuously but slowly migrates down-slope and requires hard labor to bring it back up into the field before planting crops. The other problem is soilborne diseases caused by Pseudomonas and Fusarium. To avoid these problems, we developed a hydroponics system suitable for use on sloping land. First, we tested an irrigation system in a sloped greenhouse (about m, 20 inclination). The drip tubes were set along the contour lines of the slope. The difference in elevation between the highest and lowest drippers was about 4.5 m. While the supply valve was open, the flow rates were almost same in each dripper line. However, after the valve was closed, outflow from the lowest line continued for 12 min, resulting in an extra volume of 211 ml dripper -1. We replaced all dripper lines with a dripper line that automatically stops outflow below a certain pressure and also inserted check valves into the line. As a result, outflow from the lowest line stopped only 20 s after closing the water valve, resulting in an excess of only 7 ml dripper -1. Next, we used the irrigation system to develop a hydroponics system for sloping land. Fertilizer injection and supply of nutrient solution to the plants were powered by water pressure only. Unabsorbed nutrient solution was collected into a reservoir; then used solution from the reservoir tank was mixed with fresh solution for re-use by means of an aspirator. INTRODUCTION Hilly and mountainous areas occupy about 70% of the total land area of Japan. Especially in the Shikoku area that we studied, the proportion of the land found on steep slopes is higher than the average in Japan. One of the advantages of hilly areas is cool temperatures in the summer, owing to the high altitude (about m above sea level). In many parts of Japan, it is generally too hot in the summer to produce tomatoes in a greenhouse. In Japan, tomatoes are not produced outdoors because of too much rain that causes some diseases. One advantage of sloped fields in hilly areas is that they can grow tomatoes in both summer and autumn. However, it is difficult to build a pipe-frame greenhouse, which is popular in Japan, on steeply sloped hillside fields. In hillside fields, tomato plants are commonly grown under simple rain shelters in which every row is covered by plastic sheeting. However, the exposed plants are sometimes damaged by wind and pests, and fruit cracking is increased by rain. To avoid these problems, a sloped greenhouse was developed and tested in a hillside field by our laboratory (Nagasaki et al., 2001; Nagasaki, 2002). The sloped greenhouse is made of inexpensive steel pipes 48.6 mm in diameter (which are frequently used as scaffolding in construction sites). The greenhouse has a flat roof that is almost parallel to the field. It is possible to build a greenhouse to match the crooked shape of a hillside field. Ventilation is good because of the greenhouse structure and the presence of anabatic winds. Two other serious problems in producing tomatoes occur in this area. One is that the soil continuously but slowly migrates down-slope and requires hard labor to bring it back up into the field before planting crops. This happen also in greenhouses. The other problem is soilborne diseases caused by Pseudomonas and Fusarium. In some of these areas, tomatoes have been cultivated for more than 30 years. The disease breaks out every year in Proc. IC on Greensys Eds.: G. van Straten et al. Acta Hort. 691, ISHS

2 some fields even though soil disinfectant is injected. To avoid these problems, we have developed a hydroponics system for sloping land. MATERIALS AND METHODS Drip Irrigation System in a Hillside Greenhouse A greenhouse was built on an east-southeast facing, 20 ground slope in Tokushima pref. in the Shikoku area, Japan; it was about 40 m long in the contour direction, 13 m long in the slope direction, had an area of 440 m 2 in the greenhouse (Fig. 1). Two kinds of dripper line were used in measurements of flow rate. One was Netafim (Tel-Aviv, Israel) Ram 17 (pressure-compensated, 2.3 L h -1 nominal flow rate, MPa working pressure), the other was Netafim Uniram 17 (pressure-compensated, 2.3 L h -1 flow rate, MPa working pressure, MPa shut-off pressure). The pressure-compensation mechanism in both types of tubing maintains a constant flow rate over the working pressure range. If the water pressure in Uniram tubing falls below the shut-off pressure, flow from the drippers stops and the water stays within the tubing. Twelve drip lines were placed along contour lines at alternating intervals of 1.2 or 0.8 m (Fig. 2). The difference in elevation between the highest and the lowest lines was about 4.5 m. Flow rates and volume of outflow in the different drip lines were measured under the following conditions, Experiment 1: Tubing Ram17. Experiment 2: Tubing Uniram (all lines of tubing Ram 17 was replaced with tubing Uniram). Experiment 3: Tubing Uniram, with check valves inserted into the main line (Fig. 2). Design of Hydroponics System for Sloping Land A closed hydroponics system suitable for sloping land was constructed (Fig 3) of individual Netafim PC-CNL drippers (pressure-compensated, 3 L h -1 flow rate, MPa working pressure, 0.04 MPa shut-off pressure) inserted every 0.4 m into polyethylene blank tubing with a diameter of 25 mm, fertilizer tanks, a 120-mesh Netafim disk filter, two Netafim fertilizer injectors (model 2502, 0.2 2% mixing rate, MPa working pressure), a drainage reservoir tank (1000 L), an Azone (Osaka, Japan) aspirator model , an electromagnetic valve, a timer switch. The supply of nutrient solution and injection of fertilizer were powered only by water pressure (the water source was 60 m above the greenhouse), without electric power or a pump. The cultivation beds were made of rockwool (Nittobo (Tokyo, Japan), cm) wrapped in a permeable fabric sheet to prevent root penetration and in thick plastic sheeting; it was placed directly on the ground (Fig. 4). Nutrient solution that was not absorbed by the plants drained into the lower side of the thick plastic sheeting. Cultivation beds were placed along contour lines at intervals of 2 m. The unabsorbed nutrient solution drained within the plastic sheeting along the slope of the ground into a reservoir tank. Used nutrient solution from the reservoir tank was mixed with fresh solution for re-use by means of an aspirator (Fig. 5). The mixing ratio of used to fresh nutrient solution was 22% at 0.31 MPa of water pressure. Plants and Hydroponics Cultivation Conditions We installed this hydroponics system in a sloping greenhouse belonging to a tomato grower in Tokushima, Japan. It was located on a north-facing slope, was about 27 m long in the contour direction and 10.5 m long in the slope direction, had an area of 285 m 2, and was on a 6 slope. Tomato seeds (Lycopersicon esculentum Mill. Momotaro Fight ) were sown March 2003 and transplanted to the hydroponics system on 25 April Half-strength Enshi nutrient solution was used until 29 August 2003; it consisted of 8 mm NO 3, 4 mm K +, 4 mm Ca 2+, 2 mm Mg 2+, 0.7 mm H 2 PO 4, 3 mg L 1 Fe, 0.05 mg L 1 Mn, 0.5 mg L 1 B, 0.05 mg L 1 Zn, 0.02 mg L 1 Cu, and 0.01 mg L 1 Mo (Hori, 1966). After 29 August 2003, half-strength Otsuka-SA nutrient solution was used; it consisted of 8.8 mm NO 3, 5.1 mm K +, 4.1 mm Ca 2+, 1.5 mm Mg 2+, 0.7 mm H 2 PO 4, 3 mg L 1 Fe, 0.05 mg L 1 Mn, 0.5 mg L 1 B, 0.05 mg L 1 Zn, 0.02 mg L 1 Cu, and 0.01 mg L 1 Mo. Nutrient solution 244

3 was supplied to plants 8 14 times per day, controlled by a 24-h timer. The volume of nutrient solution supplied each time was controlled manually by the grower or by us. The grower was experienced in growing tomato plants but had no previous experience with hydroponics. Harvesting of fruits was started from 1 July The main stem of the plants were topped at above the 15 th fruits truss on 22 October Cultivation and harvesting were finished at the 15 th fruits truss harvesting stage, 10 December RESULT AND DISCUSSION Development of a Drip Irrigation System for a Hillside Greenhouse When the main water valve was open, the flow rate was almost same in each dripper line and under all experimental conditions (Table 1). This occurred because the tubing that was used in these experiments includes an internal pressure-compensating mechanism to maintain a constant flow rate over a wide pressure range. However, the amount of leakage from the lowest line after closing the water valve differed among the experiments. With tubing Ram, outflow from the lowest line continued for 12 min; the total excess volume was 211 ml dripper -1. When tubing Ram was replaced with tubing Uniram, which automatically prevents outflow when the pressure falls below a certain value, outflow from the lowest line continued for only about 5 min; the volume was 83 ml dripper -1. When check valves were inserted into the main line to divide the dripper lines into sections, outflow from the lowest line in the greenhouse stopped still faster (in 0.33 min); the volume was only 7 ml dripper -1. Many studies have been made concerning drip irrigation on sloping land (Anyoji and Wu, 1985; Anyoji and Wu, 1986a; Anyoji and Wu, 1986b; Yamamoto et al, 1977). They also pointed out the outflow from lower part of the lines. We showed the dissolution of the outflow by the Uniram tubing which had shut-off mechanism and arrangement of the lines. With tubing Ram 17, the outflow amounted to the volume of solution contained within the tubing. Thus, the total outflow is expected to increase as the total drip-line length or frequency of solution supply increases. To prevent this outflow, Kawashima et al. (2000) installed an electromagnetic valve at the lowest position of the main line. After the supply of solution stopped, the solution in the tube was collected in a reservoir tank. The solution in the reservoir tank was recovered by an electric pump for reuse. Comparing the two irrigation systems, our third method, using tubing Uniram and check valves, would cost less, since no electricity supply is needed. Cultivation of Tomato Plants in the Hydroponics System A local farmer grew tomato plants for more than 7 months in a sloping greenhouse using the hydroponics system we developed. Fig. 6 shows the yield of tomato fruits, cumulative yield reached 12.8 kg m -2. The yield of tomato grown under the conventional rain shelters in this area were 6 9 kg m -2. The daily drainage rate fluctuated between 0 and 40% (Fig. 7). The 7-month average was low (7.3%) compared with that of common hydroponics (20-30%). The ph of the leaching solution decreased 7 to 5. The EC of the leaching solution fluctuated between 1.4 and 4.2 ds m -1 (data not shown). During plants growing (that is, before 30 June) and during harvesting (after 1 July), water uptake on days on which the drainage rate was >5% was related to the daily cumulative solar radiation (Fig. 8). The water uptake was calculated by subtracting the drainage volume from the supplied volume. Table 2 shows the daily cumulative solar radiation on days that the grower classed as clear, cloudy, or rainy. The grower used the weather to adjust the supply volume of nutrient solution on the day. The solar radiation for each class of weather had a broad range. Thus the control based on the grower s judgment was not appropriate occasionally. However, we expect that the grower s judgment become more accurate with experience. In our system, the mixing ratio of nutrient solutions was kept at about 20% reused drainage water obtained from the reservoir tank plus about 80% fresh solution. We think 245

4 that the resulting change in nutrient composition is smaller than what occurs in a recirculating nutrient film technique system. Feedback control based on drainage flow was found to capable of matching the supply of nutrient solution to the plants demands (Gieling et al., 2000; Higashide et al., 2002). However, automated feedback control systems are expensive for small farms, where the farmers prefer not to invest much money in hydroponics systems and greenhouses. Our hydroponics system is specifically aimed at farmers in hilly and mountainous areas. Therefore, we considered saving costs to be more important than precise control of solution supply. Indeed, in our experiment, a grower who had no previous experience in hydroponics was able to control the volume of solution supply appropriately. Several other researchers have also developed cost-saving hydroponics systems (Chikanori et. al. 1992). However, our hydroponics system, which also saves cost of installation and operating, is the first such system specifically developed for hillside greenhouses. The system does not require pumps, a large tank, electrical conductivity or ph sensors for monitoring nutrient solution, or an expensive controller, and the total cost is only about 8 9 m -2. The system does not use electric power except for the electromagnetic valve and timer, which are battery-powered. The supply of nutrient solution and injection of fertilizer is powered by only water pressure. ACKNOWLEDGEMENTS This work was accomplished as part of a research project of the National Agriculture and Bio-oriented Research Organization: Establishment of value-added production system for vegetables on sloping lands. We thank Mr. M. Tani and Mr. H. Kubo and their families for renting us a field and cooperating in the experiment, and Ms. A. Ohigashi, Mr. T. Hirata and Mr. K. Miyanishi for technical assistance. Literature Cited Anyoji, H. and Wu, I.P Study on the design of drip lateral lines. Trans. Japan. Soc. of Irrigation, Drainage and Reclamation Engineering 120:11-17 (in Japanese with English abstract). Anyoji, H. and Wu, I.P. 1986a. Study on the design of submain manifolds in drip irrigation systems. Trans. Japan. Soc. of Irrigation, Drainage and Reclamation Engineering 121:9-16 (in Japanese with English abstract). Anyoji, H. and Wu, I.P. 1986b. Study on the design of irrigation lines in a submain unit in drip irrigation systems. Trans. Japan. Soc. of Irrigation, Drainage and Reclamation Engineering 121:17-21 (in Japanese with English abstract). Chikanori, T., Abe, Y. and Homan, H Development of low-cost hydroponics using rice husk bed. Bulletin Oita Agri. Res. Center 22: (in Japanese with English abstract). Gieling, T.H., Janssen, H.J.J., Van Straten, G. and Suurmond, M Identification and simulated control of greenhouse closed water supply systems. Computers and Electronics in Agri. 26: Higashide, T., Shimaji, H. and Hamamoto, H Feedback control of nutrient solution supply based on flow rate of drainage in a mist culture of cucumber. Acta Hort. 588: Hori, Y Gravel Culture of Vegetables and Ornamental Crops. Youkendo, Tokyo, Japan, p (in Japanese). Kawashima, H., Nonaka, M. and Nagasaki, Y The drip fertigation system for vegetable cultivation in sloping greenhouses. Proceedings of the Intl. Agri. Engineering Conf. Dec. 2000, p Nagasaki, Y A consideration in farm mechanization and engineering for agriculture on sloping land. J. Japan. Soc. Agri. Machinery 64 (5):14-18 (in Japanese). Nagasaki, Y., Kawashima, H., Nonaka, M. and Matoba, K Low-cost plastic greenhouse for mountainous areas. Farming Mechanization 10:18-23 (in Japanese). Tanaka, K. and Yasui, H Studies on practical application of rockwool culture for fruit 246

5 vegetables. Bulletin Natl. Res. Inst. Vegetables, Ornamental plants and Tea 5:1-36. (in Japanese with English abstract). Yamamoto, T., Ono, J. and Cho, T An application of the drip-hose on the slow slope field. Sand Dune Res. (Japan) 23(2): (in Japanese with English abstract). Tables Table 1. Effect of type of dripper line and presence of check valves on irrigation flow rate and excess outflow in a hillside greenhouse. Experiment 1 Experiment 2 Experiment 3 Drip tube Ram Uniram Uniram Check valve no no yes Flow rate a (ml min -1 dripper -1 ) 40.5 ± ± ± 0.5 Time until flow stoppedfrom lowest line closing valve (sec) Flow volume (ml dripper -1 ) a: Mean ± S.E. (n=6) Table 2. Daily cumulative solar radiation on days classified according to weather by the grower. Cumlative Solar Radiation (MJ m 2 day -1 ) Period Clear Cloudy Rain from to Mean Max Min Mean Max Min Mean Max Min 25-Apr 30-Jun Jul 31-Aug Sep 31-Oct Nov 10-Dec Figurese Check valve Check valve 4.5 Drip tube Hillside field Main line Supply of nutrient solution 20 Fig. 1. Sloped greenhouse. Fig. 2. Arrangement of dripper lines in hillside greenhouse. 247

6 Dripper Cultivation bed Slightslope Slope Reservoir tank for drainage Aspirator W a ter Filter F ertiliz e r in je c tor 60 m Electrom agnet valve Fertilizer tanks Fig. 3. Hydroponics system for sloping land. Permeable fabric Drainage Thick plastic film Rockwool bed Slope PVC tubing Dripper Fig. 6. Tomato yield in experimental hydroponics system in sloping greenhouse. PE tubing Yield (kg m -2 day -1 ) Jun 17-Aug 6-Oct 25-Nov Date Ccumulative yield (kg m -2 ) Yield Ccumulative yield Fig. 4. Cross section of the cultivation bed. Aspirator 傾斜 Flow of nutrient solution Fig. 5. Aspirator. Drainage intake Drainage rate (%) May 3-Jul 22-Aug 11-Oct 30-Nov Date Fig. 7. Daily drainage, as percent of solution supplied. Water uptake(l plant -1 ) (After 1July) y = x R 2 = (Before 30 June) y = x R 2 = Solar radiation(mj m -2 day -1 ) Fig. 8. Relation of water uptake to daily solar radiation on days when the drainage rate was >5%. Open circles: before 30 June; filled squares: after 1 July. The water uptake was calculated by subtracting the drainage volume from the supplied volume. 248