The illustration is modified from work conducted by Heard et al. Figure 2: The uptake of phosphorus (P) by a dual-purpose hemp crop grown for seed and fiber. Research led by Manitoba crop nutrition specialist John Heard on a dual-purpose hemp crop grown for seed and fiber suggests that extra P is not required by cannabis (Fig. Plant nutrition experts are currently debating whether the P rate needs to be amplified just before flowering in cannabis to improve quality. Phosphorus concentration can be used to control excessive plant growth, but adequate levels must be provided to avoid deficiency situations. The response of Alternanthera (pictured) to increasing concentrations of phosphorus (P) from 0, 5, 10, 20 or 40 ppm (left to right). That’s why it’s important to limit excessive P applications.
Too much P will lead to excessive internode elongation and tall plants. Phosphorus is also the primary contributor to plant stretch. Providing levels below that will result in less plant growth, while concentrations above that level provide little benefit while costing more money. For a continuous fertilization program for plants grown in a soilless substrate, the target concentration is between 8 ppm and 15 ppm of P. In essence, plants require a baseline level of P to grow adequately (Fig. One of our graduate students, Josh Henry, worked on optimizing P fertilization rates for his master’s degree thesis. Phosphorous fertilization strategies have been studied extensively over the past five years. Do an evaluation of your fertilizer type by reading the fertilizer label to ensure the N form you are providing is on target. The key takeaway here is to supply most of your N from nitrate-nitrogen. After that point, most growers rely upon a nitrate-nitrogen based fertilizer. Many growers will use ammoniacal nitrogen and urea-based fertilizers during the first two weeks after plants have been transplanted into the final container to help establish the plants and encourage a flush of new growth. In commercial floriculture greenhouse production, these two forms of nitrogen are strategically deployed but are only used to a limited extent. Many organic fertilizers have N in these forms. The other two forms of N contained in most fertilizers are ammoniacal nitrogen and urea. In the cannabis industry, the market currently lacks plant growth regulators registered for use on cannabis, so you can opt for nitrate as a source for N to help avoid excessive overgrowth, also known as plant stretch. While the cost is higher, it’s the preferred form of N because it promotes compact plant growth. Nitrate-nitrogen is the main form the commercial floriculture greenhouse industry uses for its plants. Nitrogen in fertilizers primarily comes from three sources. For example, if too much P is provided, it can hinder the uptake of other elements and lead to Fe, Mn and Zn deficiencies.
Just like with human health, where we must balance our intake of sugar, protein, grains, fruits and vegetables, too much of one item can lead to imbalances in the plant due to antagonistic effects. When designing a fertility program, it is also important to keep in mind some key principles that ensure there is a nutritional balance. Providing a complete fertilizer package that contains all the essential elements is important to maximize plant growth. With cannabis production, many growers are providing Si to promote overall plant health. The quantity of macroelements and microelements required varies by type of plant, but they are all required by the plant for growth.Ĭobalt (Co), selenium (Se), silicon (Si) and sodium (Na) are four beneficial elements that promote plant growth but are not considered necessary to complete the plant life cycle. Growers must provide the remaining 14 elements to help cannabis plants thrive. They obtain hydrogen (H), oxygen (O), and carbon (C) from irrigation water or as a gas via the atmosphere. Plants require 17 essential elements for growth. Cannabis plants can thrive or struggle depending on how you design your fertilization programs. How many times have we heard that a balanced diet is essential to our health? Plant nutrition isn’t much different.
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