Today, the challenge for the hydroponic grower is to determine what can be done to make his growing system more efficient in its use of items needed to grow successfully– that is, to make the growing procedure conform to green principles. It’s not an easy task, as little is being researched today to assist growers in ways to improve the efficiency of commonly used hydroponic growing systems.
Great care is needed in the formulation and use of nutrient solutions so the elements applied are better utilized by the growing crop. For those growing systems requiring a rooting medium, minimizing the accumulation of salts in the rooting medium and reducing the requirement to periodically leach with water are green issues. What are needed are nutrient solution formulations that fit the plant species and stage of growth, as well as having use factors that result in full utilization.
Some growers add enough solution to create an effluent, which serves as a leaching of the rooting medium and partially removes that which accumulated from the previous irrigations. However, the effluent must be collected and disposed of. At one time, I was advising a greenhouse tomato grower who was using his spent nutrient solution as irrigation water for his commercial vegetable garden. It seemed like a win-win situation. But he soon noticed that the elements in the spent nutrient solution do not match the nutrient element needs of the vegetable plants Continued applications could significantly alter the fertility status of the soil, creating an imbalance among the essential plant nutrient elements. After one season, the hydroponic grower looked for another means of disposing the spent nutrient solution.
There is a way to reuse this nutrient solution effectively, however: reconstitution. Reconstitution of a nutrient solution is little practiced, as testing is required to determine its pH and elemental content (and thus what will be needed to adjust the pH and what quantity of reagents will be needed to restore the elemental content to that of the original).
For reconstitution, the nutrient solution will require filtering to remove suspended debris and sterilization in order to kill microbial organisms. Nonetheless, reconstitution can be cost-effective. It saves in water and reagents, as well as the cost associated with disposal if a spent nutrient solution is identified as being a hazardous waste.
Aside from nutrient solution, what is to be done with the rooting medium at the end of the growing period? Can it be recycled or put to some other use? A greenhouse tomato grower switched his rooting medium from perlite to composted milled pinebark.
At the end of the growing season, a local nursery purchased the pinebark for use as a potting soil for bedding and woody ornamental plants. The grower recovered the initial cost for the pinebark and reagents added during the growing season – a very profitable means of disposal. I have used spent perlite as a soil amendment in my vegetable garden, as it adds plant nutrient elements and—with continued application—is making my clay textured soil more friable.
Most hydroponic growing systems also require a reliable source of electrical power. Each time an electrically powered pump comes on to deliver a nutrient solution to the rooting medium, the cost is based on the time required to deliver the nutrient solution. Some growers use a set time method for nutrient solution delivery whether the plants have need for water or not.
Having a means of determining the water needs of the plant and applying only when needed can result in significant savings in electrical power, as well as reduced treatment requirements of the nutrient solution. Placing a water-sensing device in the rooting medium, or using a program that predicts plant water use based on measured energy inputs, makes sure water is applied only when needed.
Growers need to be aware of the real costs associated with disease and insect control—in particular, that prevention is more cost-effective (green) than having to treat for a disease or insect outbreak. It is matter of knowing what disease organisms and insects are likely to appear, and then following those procedures that will prevent unwanted outbreaks.
In general, most hydroponic growing systems are inefficient in their use of water and reagents, and have fairly high electrical power requirements. Making you current hydroponic growing systems green is a significant challenge with no easy answers.
However, as quality water becomes scare and costly, significant changes will have to be made in how water is used to efficiently deliver the essential plant nutrient elements to the rooting medium for root absorption with a minimum of lost to the environment. The ideal would be no loss– a totally green method for growing—and it’s a goal worth pursuing.