It may seem like a strange topic, but those who have been researching the hydroponic technique, establishing procedures for its application and advising growers on hydroponic growing method use, find that the efficiency of the growing method is the one aspect of hydroponics that can be the factor that leads to poor plant performance in terms of vegetative growth and product yield, and then eventually to failure. In my own experience working with hydroponic growers, failure has been a frequent occurring outcome (Jones, 2013). I have attended meetings, annual conferences and read articles addressing the future of hydroponics with glowing expectations of wide use that has yet to be realized.
There are basically 3 hydroponic growing methods in common use by growers, flood-and-drain (ebb-and-flow), nutrient film technique (NFT) and drip irrigation. Modifications of these 3 methods have been put to use in terms of their design and functional characteristics. For example, with the flood-and-drain method, the rooting vessel size, depth and rooting medium characteristics, and the nutrient solution formulation, its use factors, and monitoring and reconstitution will affect the efficiency of operation, and in turn, plant growth and product yield. For the NFT method, trough design as to its width, depth, length and slope are not fixed parameters, factors that can affect plant growth. Long session plants, such as tomato, do not grow well, while short-season crops, such as lettuce and herds can do well. Why? Because as the root mass fills the trough, nutrient solution flow is impeded, creating pockets of anaerobic conditions leading to root death, and eventually plant death. In addition, the nutrient solution formulation, and its use factors, such as recovery and reuse, will affect plant performance. For the drip irrigation method, the rooting media can be either rockwool or coir slabs, perlite, or a soilless organic mix. The rooting container may be buckets or bags when using perlite or a soilless organic mix. The operating parameters may vary depending on the crop being grown, the design of the rooting vessels, whether being operated as a “closed” or “open” hydroponic system (Jones, 2012). Monitoring of the retained solution in the rooting medium is required, measuring its electrical conductivity (EC) for determining when water leaching is required. The rate of accumulation will be greater in rockwool and coir than in perlite. Control of water retention can also be a factor that impacts plant growth, either by creating anaerobic pockets that will affect root function, or creating periods of water stress when plants are under high atmospheric demand conditions.
For the nutrient solution, the formulation may be contained in a large vessel, frequently referred to as a sump (common for the flood-and-drain and NFT methods), or as concentrates in individual vessels, being drawn from them and mixed by the use of injector pumps connected to a flowing water stream (common procedure for drip irrigation systems) (Jones, 2005). The nutrient solution after passing through either the rooting mass (as in the NFT method), or rooting medium may be either collected for reuse, with or without re-constitution, filtered and/or sterilized, or discarded to waste. A re-circulated nutrient solution will normally be water volume adjusted, monitored for its electrical conductivity (EC), adjusted as to its elemental content, or considered unsuitable for further use and discarded. For the flood-and drain hydroponic growing system, the nutrient solution will be pumped from a sump to flood the rooting medium, and then allowed to drain back into the sump. Water volume and elemental content adjustments are not fixed decisions in terms of frequency of adjustment, nor when to discard as being unsuitable for further use.
Many nutrient solution formulations lack sufficiency of some elements, too high in phosphorus (P), and insufficient in magnesium (Mg) and zinc (Zn), or not balanced among the major cations [potassium (K), calcium (Ca) and magnesium (Mg)], and containing chelates of the micronutrients, iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn), chelation being of no value when used in a water solution.
Nutrient solution use factors are frequently set so that there is an excess of elements supplied, resulting in an accumulation of ions in the root mass or rooting medium which then leads to precipitate accumulation. The frequency of application may be based on the water needs of the plants, using the nutrient solution formulation when only water is needed, that then leads to nutrient element insufficiencies. Nutrient solution formulations are not usually adjusted based on their use factors as elemental concentration should be reduced with increased application rates per irrigation and/or increased frequency of application. Most hydroponic growing systems do not provide for alternating between water only or nutrient solution, nor provide a means of diluting a nutrient solution formulation based on volume applied or frequency of application. The ideal nutrient solution formulation would be one that is balanced in terms of supplying the nutrient element requirements of the plant and no more, so as to minimize the accumulation of nutrient element ions in the root mass or rooting medium, and accumulation that will affect ion root absorption and plant nutritional status.
For maximum plant growth and product yield, the nutrient solution formulation and its use factors should match the hydroponic growing system used and the nutrient element requirement of the plant. Unfortunately, growers are not provided this type of information either by the supplier of the hydroponic growing system or nutrient solution formulators.
There is another hydroponic growing method that is used primarily for the production of lettuce and herbs, standing aerated (Jones, 2005, 2012). The parameters that can affect plant growth are the depth of the nutrient solution, method for stirring (mechanical or air), and the nutrient solution use factor in terms of volume per plant and frequency of water and nutrient element adjustment.
As mentioned earlier, the wide use of hydroponics as a growing method has yet to be realized based on past predictions, but is essentially confined to use in controlled environments, growing high cash-value crops. Hydroponics has yet to be adopted for use in uncontrolled environments by small commercial growers and home gardeners – a future that could be realized if the hydroponic growing method were efficient in its use of water and nutrient elements, and reliable in terms of plant performance.
Dr. J.B. Jones, Jr. is the author of several books including. Instructions for Growing Tomatoes in the Home Garden and Greenhouse. GroSystems, Inc., Anderson, SC (available in soft cover and e-book format for Kindle at Amazon.com)
Jones, Jr., J. Benton. 2013. Instructions for Growing Tomatoes in the Greenhouse and Home Garden. GroSystems, Inc., Anderson, SC.
Jones, Jr., J. Benton. 2012. Hydroponic Handbook: How Hydroponic Growing Systems Work. GroSystems, Inc., Anderson, SC
Jones, Jr., J. Benton. 2005. Hydroponics: A Practical Guide for the Soilless Grower. CRC Press, Inc., Boca Raton, FL.