CHOPKiNS CaFe, Mg was once a popular mnemonic for introducing students to the list of macronutrients plants need. Read as C. Hopkin’s café (is) Mighty Good, the statement includes symbols for 9 macronutrients plants need.
The mnemonic was never perfect. For example, iron (represented by the ‘Fe’ in CaFe) is really a micronutrient. Plants only need a little bit of it. Furthermore, every five to ten years or so as new discoveries are made, a new nutrient gets accepted as essential. Today, 17 nutrients (macronutrients and micronutrients combined) are widely accepted as essential for growing plants. A few others are regularly debated. These same nutrients are vital in most living creatures, because at the cellular level, the composition of things like proteins and DNA is not that different.
In a recent episode of the Microbes, Minerals, and Mindsets Podcast, agricultural educator Libby Hamilton introduced an updated version of CHOPKiNS café pneumonic. We are sharing this with you here because it is helpful to be aware of these nutrients when you are testing your soil or searching for soil amendments. Growers who want the healthiest plants with the least effort will think beyond “N-P-K” and ensure that all these mineral nutrients are present in their soil.
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The updated mnemonic reads:
“C. Hopkin’s café is managed by mine nice close couzin, Moe.
With the elemental symbols capitalized and filler letters removed, this becomes:
C HOPKiNS CaFe Mg B Mn Ni Cl Co/uZn Mo.
Grammatically, the phrase is still not perfect. For example “mine,” should say “my,” except we want it to remind the reader of “manganese,” which bares the chemical symbol, Mn. Cousin is intentionally mis-spelled in order to remind the reader of 3 different elements: cobalt (Co), copper (Cu), and zinc (Zn).
Table 1 lists all the chemical elements which are represented in the mneumonic, along with their chemical symbols. These elements are essential for plant growth, because they serve as building blocks for plant structures, or as cofactors for key metabolic enzymes. In general, the macronutrients serve structural roles, hence they are needed in large amounts. For example, about 50% of the dry weight of a plant is carbon. Micronutrients such as zinc, are needed in small amounts, because they make up the reactive centers of enzymes. These are tiny regions within specialized molecules within the plant. While they serve important functions, you just don’t need a lot of it.
To compare the amount of macronutrients and micronutrients plants need, it is helpful to imagine building a skyscraper out of concrete and steel. Concrete and steel are like the macronutrients. You need a lot of it. A micronutrient might be represented by the hinges on the door through which you enter the skyscraper. They are critical for the function of the building. A skyscraper is no good if you can’t get in and out of it. But you just don’t need the volume of hinges that you need of concrete.
Table 1. Essential plant nutrients and how they are represented in the mnemonic statement.
|Carbon (C), the C, in C. HopkinsHydrogen (H), the H, in Hopkins
Nitrogen (N), the N, in Hopkins
Oxygen (O), the O, in Hopkins
Phosphorus (P), the P, in Hopkins
Potassium (K), the K, in Hopkins
Sulfur (S), the S, in Hopkins
Calcium (Ca) the Ca in Cafe
Magnesium (Mg), the M and g in managed.
|Iron (Fe), the Fe in café
Boron (B), the B in By
Nickel (Ni), the Ni, in nice
Chlorine (Cl), the Cl, in close
Copper (Cu), the C and the u in couzin
Cobalt (Co), the C and the o in couzin
Zinc (Zn), the Z and the n in couzin
Molybdenum (Mo), the Mo in Moe
Plants may benefit from non-essential elements.
As with people, there are politics and blind spots involved in identification of essential nutrients for plants. While the need for the elements shown above has been proven repeatedly in many species of plants, it is worth noting the biology is both complex and variable. We know there are 118 elements on the periodic table, and we know that numerous elements like silicon, sodium, and selenium can play valuable biological roles. Since we are constantly learning more about the world around us, don’t be surprised if the day comes when additional nutrients are recognized as essential to plants.
Even if plants don’t need certain elements, beneficial soil microbes might.
Approximately nine out of 10 cells within a plant belong to its microbiome. Plants also interact with trillions of soil microbes. Well-fed plant and soil microbiomes support healthy plants in the production of nutrient dense food. While too much of any mineral nutrient can be toxic, successful growers find they can boost plant resilience and increase Brix readings (indicators of nutritional quality) by amending soils with rich mixtures of low level, biologically derived trace elements.