Precision irrigation, the ability to deliver calculated and measured amounts of water directly to plant roots, is a cornerstone of sustainable cultivation practices. By controlling how and when a substrate opens up irrigation channels, cultivators will become more efficient in their craft.
This increased efficiency will translate to larger profits, healthier crops, and a better chance for future generations to live a healthy and prolonged existence.
Water channelling is a natural and necessary phenomenon that allows water to drain from a substrate. Often, cultivators open up irrigation pathways, or "water channels," before the substrate is properly hydrated, causing many problems that can become quite costly. When considering the rising cost of fertilizer and freshwater, creating an economical and sustainable irrigation strategy is one of the most important factors in maintaining a profitable cultivation facility.
Managing the rate at which a substrate channels water informs your irrigation strategy and will provide substantial savings. It is no secret that prevention is much more effective than remediation. As such, deploying an unsustainable irrigation strategy results in higher irrigation inputs, increased energy consumption, and a more significant environmental impact. Therefore, applying the appropriate irrigation strategy results in monetary savings via input reductions and a healthier crop.
The Negative Effects of Water Channelling
Once a substrate begins channelling water, the controllability of the substrate greatly diminishes. However, there are other issues that compound the channelling effect; a few typical observations are dangerous: high levels of nutrition, dry sections that do not seem to rehydrate, wet sections that never seem to dry back, and sluggish growth – to name a few. On top of that, constantly wet surfaces in the growing environment are a vector for pathogens and unwanted organisms (algae). For those cultivators falling victim to channelling characteristics, excessive drain also becomes an important factor.
There are many reasons to try to manage irrigation water channelling through a substrate. Commonly, water channelling creates pockets of dryness in the rootzone, thereby damaging the roots and simultaneously inhibiting root expansion. On the other side of the spectrum, excess water around the roots may starve the plant of oxygen and increase the odds of certain pathogens (Pythium, for example) from taking hold in the substrate and plant tissue.
Dry pockets and wet pockets influence other characteristics of the substrate. For example, a previously moistened substrate that has dried out creates a situation where the dissolved salts (fertilizer) fall out of solution and remineralize. This may cause high levels of fertilizer to accumulate in those pockets, eventually dissolving back into the solution and further increasing the fertilizer levels in the substrate to dangerous levels.
Excessive drain (too much water exiting the substrate) will cause the environmental controls to work harder to remove the moisture evaporating from the growing tables or gutters and into the atmosphere. Increased usage of the climate controls may result in increased operating costs. Water that drains to waste is expensive, mainly due to the inherent cost of fresh water and fertilizer. Recapturing, treating, and recirculating drain water requires special equipment and space, which is expensive to operate and maintain. It is imperative to find the proper balance.
Watch Out for False Drain
Another important reason to understand drain is that false drain (drain that occurs before the desired water content is achieved) often causes the cultivator to chase their tail. They begin to reach drain sooner than they should, notice the EC climbing towards dangerous levels, and try to lower the nutrient build-up. The increased irrigation frequency encourages the water to channel straight through the substrate. When the substrate does not appear to be increasing in WC, more water is delivered to the plant, which further compounds the problem.
The Benefit of Grodan Stone Wool
Fortunately for cultivators using Grodan stone wool, the characteristics of the substrate allow for easier rootzone management. Grodan stone wool has a very low CEC (Cation Exchange Capacity), measuring how easily particles can bind to the substrate. Specifically, a low CEC means that stone wool does not absorb and hold onto nutrients like other substrates. As a result, it is easier to refresh the nutrition within the rootzone. This feature requires the cultivator to deploy water in a calculated and precise fashion, typically by drip irrigation. Drip irrigation allows the cultivator to directly supply the roots with water and fertilizer, eliminating the misplacement of nutrient-enriched water on the growing benches and floors.
To help eliminate the propensity of water channelling in the rootzone, Grodan has devised a multi-phase model, guiding cultivators to alleviate channelling, manage the nutrition in the rootzone, and steer the crops' desired growth characteristics more efficiently. Phase one (P1), the first irrigation until drain, assists the cultivator in building up the desired water content in the substrate. Phase two (P2), the first drainage event until the last irrigation of the day, assists in modulating the water content and the management of nutrition in the rootzone. Phase three (P3), after the final irrigation of the day and the first irrigation of the following morning, allows the cultivator to trigger certain metabolic events (vegetative/generative) to obtain desired growth characteristics.
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