Macronutrients — E T H O S

In crop production, the difference between a good cannabis crop with an adequate yield and a great cannabis crop with a fantastic yield is a farmer who understands nutrients— and how to manage them to maximize a cannabis plant's genetic potential.

Liebig's Law of the Minimum says that a crop will only produce as well as its most deficient factor will allow, even if everything else—from the genetics to the environment and medium—are perfect. Crop managers tend to focus primarily on nutrients, and not all the other photosynthetic-limiting factors, because other limiting factors such as pests, temperature, water and CO2 are relatively easy to control. Nutrient management, on the other hand, is a learned skill that can be hard to grasp immediately.

Understanding each nutrient and its role in healthy plants starts with the 18 essential plant nutrients.

The essential plant nutrients are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen (O), hydrogen (H), iron (Fe), boron (B), chlorine (Cl), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), and cobalt (Co).

These 18 elements are a must for complex plant functions related to rapid growth, including being precursors to plant hormones, enzymes, amino acids and proteins.

Essential nutrients breakdown into macro and micro nutrients. Within these 2 classifications, there is a third group of nutrients called secondary macronutrients. Keep in mind, all 18 nutrients are essential to plant growth, but macro and micro simply define which nutrients a plant requires more or less of, respectively, throughout its lifetime. These prefixes do not define the importance of a particular nutrient over another nutrient in a management system. Plants require them all.

Let’s start with expanding our understanding of the macronutrients group, which consists of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen (O), and hydrogen (H).

Primary Macronutrients

Nitrogen

Nitrogen is the workhorse of the plant nutrients, not only because of the sheer volume needed by a plant through its vegetative and flowering stages, but also because nitrogen helps to capture the sun's energy for the whole photosynthesis process.

Nitrogen is so abundant in plants that it is found in every plant cell. This means that healthy cannabis leaf analysis will usually come back between 3-5% nitrogen. This wide distribution throughout a plant is necessary since nitrogen is a key component of biochemicals like chlorophyll, amino acids, protein, hormones and protoplasm. These biochemicals all play a vital role in plant cycles like the Kreb’s Cycle or the Calvin-Benson Cycle, which is how plants create sugars, ATP, NADH, and FADH which all power its other internal processes.

Cannabis plants will use most of their nitrogen in the vegetative stage of growth to collect the energy needed to quickly make stems, roots, and leafy, green canopy growth.

As plants transition into flower, they use less nitrogen after week two than they would during vegetative growth, but nitrogen is still required to fuel a plant's rapid cellular growth for flowering. This is why nitrogen is considered the biggest limiting factor for nutrient management, and why it's important to nip nitrogen deficiency in the bud as early as possible to avoid stunted yields.

When antagonized in the soil, nitrogen becomes a mobile nutrient within the plant, which means plants can translocate it to any other part of the plant. Nitrogen’s importance means that if a plant must, it will translocate nitrogen away from other important processes to areas deemed more vital in its internal triage.

Phosphorous

Phosphorus is a major constituent of nucleic acid and phospholipids, which means it’s part of DNA and RNA, and is crucial to the transfer process between new cells.

Much like nitrogen, phosphorus is found in every cell of a plant. In plant cells, phosphorus acts like a battery, storing and transferring energy around as needed, regulating the energy usage in a plant. After nitrogen helps capture and produce ATP energy, phosphorus acts as a glue that holds the ATP together in chains until it’s needed to power other internal plant processes. Unlike nitrogen, despite phosphorus being in high demand by plants, it makes up only .25-.50% of a healthy cannabis leaf analysis sample.

With crop production, when it comes to phosphorus, having a large, robust root system is crucial to healthy plants and large yields.

Unlike other macronutrients, the bulk of phosphorus is not stored in a cannabis plant’s leaves, as we saw with the leaf analysis, but in its root system. This is true especially during vegetative growth. After a plant begins to flower, however, phosphorus is rapidly translocated away from a plant’s root system to its flowers. Once flowering begins, 80% of phosphorus found in a cannabis plant’s biomass is found in its flowers. This is why phosphorus fertilization rates go up with a transition to flower as nitrogen fertilizer rates go down.

Phosphorus is fundamental to cannabis flowering. Phosphorus is considered the second highest plant nutrient limiting factor behind nitrogen. This is due to the fact that if a soil has too much clay or minerals, phosphorus can get tied up where it’s unavailable to a plant.

Potassium

Potassium is the driver of physiological processes in cannabis plants, and is an activator of over 60 enzymes that synthesize important plant biochemicals.

Potassium, through osmoregulation, is needed for the movement of water throughout a plant, from the roots to the leaves. Regulating water means potassium also affects the movement of nutrients and sugars throughout a plant as well.

Potassium, by way of potassium pumps and guard cells, controls the opening and closing of plant stomata.

Stomata are pores on a leaf where gasses are exchanged with the atmosphere. This means potassium is crucial to CO2 intake as well. Regulating water, nutrients, sugars and CO2 means potassium works to affect the rate of photosynthesis in a plant, speeding it up or slowing it down. Potassium’s importance to a plant’s physical functions mean that in a leaf analysis, potassium makes up 1.5-3.0% of a healthy sample.

Potassium aids in healthy root growth during the vegetative growth and early flowering stages.

Potassium itself is not linked directly to cannabis flower production the same way phosphorus and nitrogen are. However, since potassium is tied to so many important internal processes, such as the rate of photosynthesis and water uptake, deficiency in the soil will indirectly cause stunted flowers.

Since potassium is a mobile nutrient, any soil deficiencies will cause it to translocate away from other important areas, like stomata control.

If CO2 or high intensity lights are being used, proper potassium management is a must, or else a plant won’t be able to keep up with the added nutrient demands of increased photosynthesis rates. Potassium is the last of the three nutrients in the primary macronutrients category that manages control.

Oxygen, Hydrogen & Carbon

Oxygen, hydrogen, and carbon are macronutrients as well, but these are less of a concern to crop managers because plants take most of what they need of these elements from the atmosphere. This means simple environmental corrections in greenhouses or indoor spaces would correct any deficiencies in these areas.

Secondary Macronutrients

Secondary macronutrients are used by plants in larger quantities than the trace micronutrients, but not as much as the three primary macronutrients.

Calcium

Calcium is a unique nutrient in cannabis. Not only does it play an important role as a structural component, but it has an even more important role as a second messenger signaler. Second messenger signals are molecules released into signaling networks by a plant as a response to environmental or internal stimuli. In this case, the second message calcium molecules bind with proteins to form instructions on what cellular response is needed. This calcium signaling network in cannabis helps to regulate important developmental, physical, and stress responses—even nutrient uptake signaling. This network depends on calcium being available in the plant at all times, which means cannabis’ demands for it are high. So even though calcium is a secondary macronutrient, receiving a leaf analysis result with calcium levels between 2.0-5.0% should not be surprising.

Magnesium

Magnesium is important to plants for a host of physical and biochemical reasons such as root development and photosynthesis. This is possible because magnesium is a transporter of photoassimilates. One of these important photoassimilates in particular is sucrose, which is produced in leaves during photosynthesis and is moved by magnesium all around a plant, even down to the roots. This is really important to a plant, especially in early vegetative growth stages when the plant is developing roots and setting its shoots. Magnesium deficiencies in early vegetative growth can be hard to overcome later in a plant's life and can set yields back, because once flowering is initiated, establishing new shoots and roots slows down and stops completely. Magnesium is a secondary macronutrient in terms of needed volume , only composing .30-.81% of a leaf analysis sample, but is extremely important to a plant’s overall health.

Sulfur

Sulfur’s role in plant growth is so important that some nutrient manufacturers will list a product’s sulfur percentages next to N-P-K percentages on the label. It’s often referred to as the 4th major plant nutrient. This is because sulfur is important to the formation of 2 of the 21 amino acids, while also activating particular vitamins and enzymes needed for plant growth. Some of these sulfur enzymes combine with nitrogen to create chlorophyll, the star of photosynthesis. Furthermore, sulfur's role in nitrogen metabolization cannot be overlooked, making nitrogen fertilizer usage more efficient. With cannabis in particular, sulfur is very important because of the role it plays as a precursor to oils and terpenoids of cannabis flowers. Sulfur is the last of the secondary macronutrients, coming in at .17-.38% of a leaf analysis sample.

Organic vs. Synthetic (Mineral) Nutrients

I want to take a quick moment to touch on a sensitive subject in the cannabis community: organic versus synthetic nutrients.

The plant does not know the difference between organic or synthetic nutrients, because plants almost exclusively take up nutrients in an inorganic ionic form.

Synthetic nutrients come “ready to use” as soluble inorganic ions, while organic inputs need a soil micro-herd to decompose them into their final soluble, inorganic ionic state. From this point, once these nutrients reach plant roots and are taken up into the plant there is no difference between them.

The argument for organics goes beyond nutrients.

Soil microbes and plant roots work symbiotically to help improve other aspects of a plant’s overall health. These and other organic compounds also help raise a plant's terpene production by encouraging the release of root exudates, secondary metabolites, enzymes and other beneficial plant and microbial compounds.

Sources:

Suchoff, David, et al. “Hemp Leaf Tissue Nutrient Ranges: Refinement of Reference Standards for Floral Hemp.” NC State Extension Publications, NC Cooperative Extension, 4 Nov. 2021, https://content.ces.ncsu.edu/hemp-leaf-tissue-nutrient-ranges.

C.,, Weil. Ray R. Brady, Nyle, and Ray R. Weil. The Nature and Properties of Soils. 15th ed., Pearson, 2016.

Seiter, Stefan. “Soil Chemistry and Fertility Lecture.” Crop Production. 2017, Albany, Oregon, LBCC.

Pictures for article

Nitrogen Cycling