Prioritizing Plant Nutrients
For conventional farmers, Nitrogen (N)-Phosphorus (P)-and Potassium (K) seem to be the big three nutrients. These three macronutrients consume most of the fertilizer budget, especially on corn and small grains. Nitrogen (N) is used to make protein, P is used for DNA, RNA, cell walls, and for energy transfer (ATP). Potassium (K) is used like money in the plant, involved in nutrient exchange and balancing electrical charges.
Next, secondary nutrients are Calcium (Ca)-Sulfur (S), and Magnesium (Mg). Calcium (Ca) is a major regulator of plant hormones and growth. Calcium carbonate or lime is used to balance pH, just slightly acid. Sulfur (S) is needed with nitrogen to make essential amino acids for protein synthesis. For most farmers, unless you have sandy soil, you have plenty of Mg so it is considered a free nutrient, seldom supplemented. High Mg soil test levels in clay soils usually indicate poor soil structure and compaction, so farmers generally regard this nutrient rather poorly.
Then there are numerous micro nutrients: Manganese (Mn), Zinc (Zn), Copper (Cu), and Boron (B). Also Iron (Fe), like Mg; when found in high amounts, contributes to poor structure. At the bottom are three major nutrients used in the highest amount in plants: Carbon (C), Oxygen (O), and Hydrogen (H); but these are free nutrients, so why worry about them? Chlorine (Cl) and Molybdenum (Mo) are two more micronutrients. Do we have our priorities mixed up?
Dr. James White, Microbiologist from Rutgers University, puts forth a different framework for prioritizing soil and plant nutrients. His priorities align more with long-term no-till, cover crops, and soil health. His first priority is maximizing C or CARBON. All plant sugars produced from photosynthesis need C as the building block. It is the most limiting nutrient. Most plants use up their supply of C as carbon dioxide within 1–2 hours after sunrise. Adequate CARBON is essential for higher crop production.
The next priority is Oxygen (O) and Hydrogen (H). Oxygen is used for root respiration or energy transfers. Water is split into OH- and H+ by Mn2+. The hydroxyl group (OH-) and hydrogen ion (H+) are used to form glucose, proteins, enzymes, hormones, and vitamins. However, none of this can be accomplished without photosynthesis. Iron is used to activate the photosynthesis enzyme making chlorophyll and Mg is the central element in the chlorophyll molecule. Adding foliar applications (use ionic water + fulvic acid) of Fe2+ and Mg2+ in the spring makes plants turn dark green, almost blue. Often corn looks pale yellow in the spring when soils are cold and wet. Is it N deficiency or a lack of Fe and Mg? Ironically, Fe is needed for adequate N uptake and assimilation.
Calcium (Ca) is the third largest nutrient in most plants and Ca needs B to be the bus driver to get Ca into the plant. Calcium regulates growth hormones (auxin) and yield hormones (cytokinins) through gibberellins activated by Ca. Adequate Ca is critical! After Ca, S is needed to make critical proteins. Copper is needed to activate enzymes for lignin and stalk strength. Zinc comes after N and is ranked 10th. Adequate Zn is needed to prevent disease and insect damage to plants.
Farmers might argue, but N-P-K are ranked 9th, 11th, and 12th according to Dr. White — probably because almost 50% of the N and P comes from soil microbes associated with the plant root. Potassium (K) is not part of any organic molecule in the plant. It is strictly used like money to swap out for other nutrients and to maintain an electrical (+, -) balance in the plant. While N and K are two of the most used plant nutrients, with good soil health, they are generally readily available. Each soil microbe is a soluble bag of fertilizer supplying all these nutrients to the plant. Without good soil health and good soil structure, farmers have to supply more N-P-K as fertilizer. Using good soil health principles, farmers get more plant available nutrients supplied through the microbes.
Often, it is the other micronutrients which are limiting. Micro nutrients make up less than 2% of all nutrients needed in the plant, but they are critical for turning proteins into three-dimensional enzymes, hormones, and vitamins, which speed up biological processes. The priorities for maximizing crop yield tend to differ for conventional tillage farmers versus no-till, cover crop soil health farmers; but the priorities for good healthy plants and food should be the same.
