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Defining Malnutrition in DWC Hydroponic Systems

From ‘more is more’ to ‘less is more’, deep water culture growers are now settling in the middle when it comes to plant nutrition. Lacey Macri looks past the trends to provide insight on finding a balance for feeding DWC plants. For years, people were under the impression that size does matter thanks to Godzilla’s powerful marketing slogan. Fast food chains even climbed on board, offering super-sized this and that to consumers, making a huge push toward the more is more principle. As time went on, consumers began recognizing this strategy as a money-making scheme to sell more product, which then spawned the next revolution: less is more. Just as those at the top had previously done, less- is-more enthusiasts began doing the same, limiting their consumption in many areas of their lives toward a more sustainable existence. Crop cultivators eventually followed the trends of both campaigns, but as soon as science-based evidence was brought to the surface regarding the ineffectiveness of overfertilization, the less-is-more mentality began making its way into crop cultivation as well. DEFICIENCIES IN DWC While less-is-more can be highly effective in many arenas, it has started to become overhyped and overemphasized in some cases. I will focus the conversation on the undernourishment of plants in a deep water culture environment. Although it is true that plants in a DWC setting can flourish with less nutrients than plants in other hydroponic and soil settings, there is always a threshold that needs to be maintained. When it comes to feeding your plants appropriately, the range for optimal nourishment is narrow. When growers subject their plants to the lower end of what is normal or even outside of that range, symptoms of deficiency will likely occur. Signs of deficiency can vary depend- ing on which nutrient(s) the plants are lacking. In comparison to nutrient toxicities, deficiencies may manifest in a more isolated manner. For example, plants that are overfed will likely exhibit multiple symptoms simultaneously, demonstrating toxic levels of more than one element and will look like they are dying. Deficiencies tend to be harder to spot because the plants may be getting enough of one element but not another, producing plants that may look healthy overall, but not quite right. The progres- sion of deficiency worsens over time, so early stages may be hard to recognize until the problem has advanced signifi- cantly. In this scenario, nutrient lockout becomes a major concern because the plants may selectively uptake sufficient quantities of one element but fail to nourish their need for another. A key to understanding deficiencies is being familiar with mobile versus immobile nutrients. Once immobile nutrients are taken up by the plant and directed to where they are needed, they tend to remain in that place indefinitely. This is why deficiency symptoms of immobile nutrients manifest in the newer growth because that deficient nutrient remains immobilized in another area of the plant, unable to move to the area of need. Some examples of immobile nutrients include calcium, sulfur and iron. Mobile nutrients on the other hand will display deficiency symptoms in the older leaves as they are able to penetrate through the plant to the areas of new growth where they are needed to continue growing. Mobile nutrients include nitrogen, phosphorus, potassium and magnesium. Different crops and different strains of the same crop will also all have their own set of demands for nutrition, so there will always be somewhat of a learning curve when growing something for the first time. pH SWINGS Another cause for concern is pH insta- bility when underfeeding your plants in a DWC setting. The mineral ratios in many of the hydroponic nutrient formu- las on the market have been previously calculated to deliver a product that has already been buffered by the ingredi- ents themselves. When growers use substantially less than the manufacturer advises, the buffering capacity of these formulas is compromised, leading to pH instability. This can be easily fixed by upping the dosage to produce a nutrient solution that matches the target EC or total dissolved solids (TDS) listed by the manufacturer. Keep in mind, if the plants already began exhibiting symptoms of pH imbalances or nutrient deficiencies, it may take three to seven days for the new growth to appear healthy again after the solution has been adjusted. Most changes brought on by nutrient imbalances do not happen overnight. IS ‘LESS-IS-MORE’ DEAD? Not at all! However, in some instances it does need to be reined in so as to not go overboard with underfeed-ing. The less-is-more principle found its place in DWC because it offers a unique environment for plants whereby ion exchange is more easily facili- tated. Increased levels of dissolved oxygen in DWC also plays a role in increased nutrient uptake. Roots that are suspended indefinitely in a DWC system are provided with ample oxygen through various sources such as air pumps, air stones, and ozone injection. Maintaining cool water temperatures is crucial to holding the dissolved oxygen in place so that it is readily available to the plant during uptake. Colder, deeper water temperatures have the ability to hold higher concentrations of dissolved oxygen. Roots exposed to higher levels of oxygen will uptake nutrients more rapidly, expediting plant processes in general. That is why you will often notice plants in hydroponics tend to grow larger faster than those in soil. Keep in mind that bad things will also permeate through the entire system faster, too. If your goal is to grow large plants, the best practice is to push them to their highest uptake potential at the upper end of the optimal range without over- feeding. Some growers will even feed their plants until they see the slightest sign of downward leaf curl, indicating over-fertilization. At that point, it’s time to back off and let the plants do their thing. Starving your plants though, will make bulking very difficult.