Water Culture. In the water-culture method, plants are supplied with mineral nutrients directly from a water solution. The chief advantage of this method over aggregate culture is that a large volume of solution is always in contact with the root system, providing an adequate water and nutrient supply. The major disadvantages are the difficulties of providing an air supply (oxygen) for the plant roots and proper support and root anchorage for the plants.
Materials and Equipment. The cost of growing plants through hydroponics depends upon the cost of chemicals and water used in the preparation of the nutrient solutions, the size of the operation, and the amount of mechanization. The cost may be quite low if you have a small setup and use available materials.
For a large setup, you will need a tank or through constructed of concrete or wood. A depth of 6 to 18 inches and a width of 2 to 3 feet are the most common sizes for the larger tanks. If you use wood, be sure that it is free of knots and sealed with asphalt that does not contain creosote or tars. Do not use asphalt that leaves an oil film on the surface of the water. If the system is small, you can use glass jars, earthenware crocks, or metal containers. Metal containers should be well painted on the inside with an asphalt-base paint. Glass jars must be painted on the outside with dark paint to keep out light. A narrow strip should be left unpainted so that the level of the solution can be seen in the glass container.
The seedbed or plant bed should be 3 or more inches deep and large enough to completely cover the trough or tank. To support the litter, cover the bottom of the bed with chicken wire or 1/2-inch-mesh hardware cloth painted with an asphalt-base paint. Fill the bed with litter. The litter may be of wood shavings, excelsior, sphagnum moss, peat, or some other organic material or matter fairly resistant to decay. Germinate the seed in sand or vermiculite and transplant to the water-culture bed. Keep the bed moist until the plants get their roots down into the nutrient solution.
Aeration. The water-culture method often fails because of inadequate aeration of the solution. The space between the seed bed and the nutrient solution may provide enough air for the roots of certain plants. But you must make special provision to allow an exchange of air between this space and the air outside. Prop up the seed bed a fraction of an inch or drill holes in the container or tank just above the highest solution level.
If you have trouble aerating the roots, use an aquarium air pump. Do not stir the solution too vigorously. You may damage the tender roots and cause poor plant growth. Pumping the air through an air stone, a perforated pipe, a porous glass tube, or a hose covered with a fine screen will reduce root damage by breaking down the air bubbles.
Water Supply. An adequate supply of pure water is essential for this system of hydroponics. The mineral content of water varies from place to place. In some areas, water is softened by replacing the calcium and magnesium with sodium. Sodium is toxic to certain plants when present at high levels. Boron and copper may be toxic at very low levels in the water, even though these elements are required in minute quantities for plant growth. Usually the minerals in water are not detrimental to plant growth. Calcium and magnesium, which are often present in water, are beneficial to plants.
Applying Nutrient Solution. Nutrient solution may be added by hand, by means of a gravity feed system, or mechanically. In a small setup, the nutrient solution can be mixed in small containers and added by hand as needed. In a large setup, the gravity-feed system can be used effectively. The nutrient solution is mixed in a vat and tapped from the vat as needed. A large earthen jar or barrel will serve as the vat. If you use a metal barrel or container, paint the inside with an asphalt-base paint.
A pump can be used to transfer the material from the mixing vats to the growing tanks. Use a special non-rusting pump, or wash the pump carefully after each use. This precaution is necessary because the chemicals used in the nutrient solution will corrode metal.
The time to add nutrient solution depends upon the temperature the growth of the plants. When the plants are young, the space between the seedbed and the nutrient solution may be quite small (sometimes one-half inch is sufficient). As the plant roots grow, lower the nutrient level slowly, keeping the level of the solution as constant as possible.
When the temperature is high and evaporation rapid, the plants may need additional solution every day. Keep the roots at the correct level in the water. The roots will die if allowed to dry out.
The container ar tank should be drained completely every two weeks and the nutrient solution renewed from the mixing vats. This operation should be arranged so that it can be accomplished in a short time. If more than a few minutes elapse between the time of draining the tanks and refilling them, the roots will dry out. To delay the drying of the roots, change the solutions on a cloudy day or after the sun has gone down.
Transplanting seedlings or seeding directly into the seedbed will get the plants growing under the solution-culture system. The litter must be kept moist until the roots become established in the nutrient solution. Transplant seedlings carefully. Work the roots through the support netting into the nutrient solution; then build the litter around the plant to support it.
SYSTEMS OF SOILLESS CULTURE
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