Hydroponic Tomato Growing

There are 3 hydroponic growing systems suitable for the hydroponic growing of tomato plants. Initially, the ebb-and-flow method (or modifications of the technique) was the method in use from the late 1930s into the 1970s. In the mid-1970s, Allan Cooper introduced his nutrient film technique (NFT) that substantially changed the basic concept of hydroponic growing, eliminating the need of a rooting medium, with the plant roots being periodically bathed in a flow of nutrient solution.

With the introduction of drip irrigation, water and nutrient solution (combined with fertilizer injector systems) could be placed at the base of the tomato plant. Initially perlite, in either bags or buckets, was the rooting medium of choice with rockwool slabs, and more recently coconut coir slabs, are now in widest use.

All of the currently used hydroponic techniques have flaws that have to be dealt with. The “ideal” hydroponic growing system has yet to be developed, although initially the NFT method was thought to be the one that would come closest.

There are two systems for handling the nutrient solution, an “open” system in which sufficient nutrient solution is applied to the rooting medium necessary to keep it moist with minimal or little runoff, and for the “closed” system, the nutrient solution delivered to the rooting medium is in excess and is recovered for reuse.

Ebb-and-Flow (Flood-and-Drain)
Sometimes referred to as flood-and-drain, a water-tight growing bed, containing either clean gravel or course sand as the rooting medium, is periodically flooded for a short period (5 to 10 minutes) with a nutrient solution pumped from a supply tank. By placing the nutrient solution supply tank below the growing bed, the nutrient solution can drain back by gravity. This hydroponic growing system is little used today other than for hobby-type systems. The method is inefficient in its use of water and plant nutrient reagents. Root disease occurrence and nutrient element insufficiencies can occur with repeated use of the nutrient solution. Being a “closed” system, the re-circulated nutrient solution will require reconstitution, filtering, and sterilization. Within the growing period, the nutrient solution may require replacement. The rooting medium will require washing to remove root debris and accumulated precipitates as well as sterilization before reuse

Nutrient Film Technique (NFT)
A germination cube containing a tomato seedling is set in a sloping trough of flowing nutrient solution. The trough can be made of framed material or consist of a plastic sheet that is pulled up over the cube, enclosing it in a pyramid-shaped trough. The slope of the trough and the rate of nutrient solution flow down the trough will affect each plant differently depending on its position in the trough (at the head or base). As roots fill the trough, the flow of nutrient solution down the sloping trough becomes restricted, either the nutrient solution flows over the top of the root mass or down its sides. The center of the root mass can become anaerobic with roots beginning to die from lack of sufficient oxygen. Disease and nutritional problems can easily occur. Being a “closed” system, the re-circulated nutrient solution will require reconstitution, filtering, and sterilization. Within the growing period, the nutrient solution may require replacement. The NFT method is inefficient in its use of water and nutrient element reagents.

Although still used by some for growing tomatoes, the NFT method is not suitable for use with long-term crops that will fill the trough with roots, resulting in the potential for a crop loss due to “root death,” lack of oxygen, and the potential for root disease occurrence.

Drip Irrigation
Today, this is the method used for growing tomato plants hydroponically. A seedling is placed in either perlite in bags or buckets (BATO buckets in most use), or a rooted seedling in a rockwool block is set on a rockwool or coconut coir slab. Currently, rockwool is the preferred rooting medium for this method for the hydroponic growing of tomato.

A nutrient solution is delivered at the base of the plant with sufficient volume so that there is some solution flow out the base of the bag, bucket, or slab that requires disposal, but is not recovered for reuse, therefore being an “open” system. The management of the growing system in terms of nutrient solution composition, frequency and amount delivered to the plant is based on environmental factors, such as air temperature and light conditions as well as stage of plant growth (non-fruiting or fruiting).

That portion of the nutrient solution retained in the rooting media is periodically monitored for its electrical conductivity (EC), and when the EC reaches a certain level, the retained solution is removed by leaching with water applied through the drip irrigation system. An environmentally acceptable means of disposal of the leach effluent maybe required.

Nutrient Solution Elemental Composition

The 13 mineral elements required by plants, the major elements being nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (8), and the micronutrients being boron (B), chlorine (CI), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (2n), must be in their proper concentration and ratio in a nutrient solution formulation. Commonly used nutrient solution formulations are given in various reference books (see the section: Books and Videos). The quality of the water used to irrigate and make a nutrient solution should be determined before use, and if found containing undesirable constituents, be either treated to remove them, or another water source found. Some water sources may contain an essential element or elements, such as calcium (Ca) and magnesium (Mg) that can reduce the reagent requirements when formulating a nutrient solution. Reagents selected to formulate a nutrient solution should be relatively free of unwanted constituents.

Nutrient Solution Use Factors

Maintaining the nutrient element status of the tomato plant in order to keep it productive over an extended period of time is the challenge. The initial composition of the nutrient solution, its frequency of delivery and volume applied with each irrigation, will affect the nutrient element status of the tomato plant. Adjust-ments in the nutrient solution composition and delivery schedule may be required with the changing status of the plant and due to changed environmental conditions. A sample of effluent from the rooting medium with each nutrient solution irrigation may be collected for pH and element content determination so that adjustments can be made in the applied nutrient solution to correct insufficiencies and to minimize the accumulation of nutrient elements in the rooting medium. For “closed” systems, the re-circulated nutrient solution requires reconstitution, filtering and sterilization before reuse.