Development of closed, energy-saving hydroponics for sloping land

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 13 x 40 m, 20 degrees 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.