Why do we need fertilizers?

Plants are living beings and, just like us humans, require nutrients to build their bodies and power their cellular processes. Nutrients are simply atoms, such as nitrogen, calcium, iron and all of the others on the periodic table. We call them nutrients when they are involved in nutrition, but those atoms are the same whether they are in the atmosphere, a rock, a plant, an animal or in us. I like to imagine that atoms are like Lego pieces snapped off from one location and snapped into place somewhere else.

Without nutrients, living beings wouldn’t be able to grow, defend themselves, reproduce, or… well… do anything. However,  the presence of nutrients alone isn’t enough. Issues also arise because they are not available in the right quantity and/or ratio with other nutrients. This affects cellular processes and can lead to an observable variation from normal, which we call a “symptom”.  In humans, iron deficiency can lead to a condition called anemia, in which the body has difficulty carrying oxygen because iron is a key atom in the structure of red blood cells. Likewise, iodine deficiency can lead to an enlarged thyroid gland in the throat, which we call a goiter. Plants are no different and exhibit patterns of symptoms when nutrient levels are out of whack.

Nitrogen deficiency in corn shows up as a V-shaped yellowing of the leaf.
Potassium deficiency in corn shows up as a yellowing of the outer margins of the leaf.
Phosphorus deficiency in corn shows up as a purpling of the leaf.

So, what are fertilizers?

Fertilizers are substances containing nutrients that plants can absorb either through their leaves or roots. Depending on how “fertilizer” is exactly defined,  compost and manure may not be called fertilizers because those products are considered to feed the soil, while fertilizers feed the plant more directly. Either way, compost and manure contain nutrients that can be made available to plants through microbial digestion, albeit much more slowly.


Fertilizers sprayed onto leaves are called “foliar” because it goes on the foliage. Fertilizer can also be applied on top or in the soil for the root to uptake the nutrients it contains. Nitrogen (N), phosphorus (P) and potassium (K) are the most common nutrient fertilizers applied to agricultural plants. These nutrients are considered macro-nutrients because plants need them in the greatest quantity.


NPK fertilizers will have three numbers separated by dashes, indicating how much of each nutrient is contained within it, by weight. N is the first value, followed by P and then K. There is one tricky point to remember when calculating the actual amount of each nutrient, however. The first value is the true amount of nitrogen, but phosphorus and potassium need to be converted.   Phosphorus’ value is reported as the weight of phosphorus pentoxide (P2O5), so that value is actually 43.6% phosphorus. Potassium’s value is based off of the weight of potassium oxide (K2O), so that value is actually 83% potassium.1 To see what I mean, let’s assume the weight of the bag below is 100 pounds. This means that it contains 10 pounds of nitrogen, 10 pounds of P2O5 (4.36 pounds of P) and 10 pounds K2O  (8.3 pounds of K).

All purpose fertilizer (10-10-10)

Common fertilizers applied to farms and ranches are urea (46-0-0), anhydrous ammonia (82-0-0), Monoammonium phosphate “MAP” (11-48-00 to 11-55-00), Diammonium phosphate “DAP” (18-46-00 to 21-56-00), Muriate of potash (00-00-60) and potassium nitrate (13-00-44).

Anhydrous ammonia gas contained in a high pressure white tank is knifed into the ground.
Monoammonium phosphate, "MAP", granules
Muriate of potash granules

Although they have garnered the lion’s share of attention, N, P and K are not the only nutrients that plants need. Magnesium (Mg), Calcium (Ca) and Sulfur (S) are considered  secondary macro-nutrients, while all others are considered micro-nutrients because they are needed in very small quantities. This does not mean they are less important than the macro-nutrients! Far from it. Micro-nutrients are essential for the proper functioning of nearly every cellular process in plants. For example, Zinc (Zn) and Manganese (Mn) are essential during photosynthesis and Boron (B) is needed for strong cell walls. Modern agriculture is slowly moving away from a solely NPK mindset to one that looks at the quantity of every nutrient and their balance with each other.

Inorganic vs Organic Fertilizer

Organic simply refers to carbon (C). Fertilizers that do not contain carbon are inorganic. For the most part, plants take up nutrients in their inorganic forms, although current research may be turning that statement on its head.2 Most inorganic fertilizers are produced in an industrial setting, which is why you might hear the term “synthetic”, inorganic fertilizers. Many of these processes to make inorganic fertilizers involve concentrating nutrients held within rock minerals. Others involve separating nutrients from gases, such as with synthetic nitrogen production (air is 78% nitrogen!). These nutrients are then applied to the plant, taken up and combined with other nutrients, especially C. The nutrients are now in an organic form.


Organic fertilizers are those where nutrients are still attached to C. For the most part, the nutrients need to be set free from these bigger, bulkier carbon compounds in order for the plant to uptake them. This means that nutrient concentration is lower and release is slower in organic fertilizers compared to synthetic, inorganic fertilizers. Soil microbes are necessary for the process of setting nutrients free into simple forms. This is called “mineralization”.


Certified Organic growers in the United States must use fertilizers that meet standards in the National List by the USDA National Organic Program. The Organic Materials Review Institute is a private organization that evaluates and endorses products that meet these standards. Common organic fertilizers include fish meal (9-5-4), bone meal (3-20-00), and kelp (1-1-7)3. These NPK values are approximate and can fluctuate by product. Compost and manure application is also very common among organic producers. It should be mentioned again that not everyone considers them fertilizers, as they do not immediately provide a dose of inorganic nutrients. Whatever you call them, the same mineralization process occurs when they are applied to the soil and nutrients are put into the soil ecosystem that were not previously there. There is a potential benefit to this “low and slow” approach to feeding a crop throughout the growing season as mineralization occurs. For example, water-soluble inorganic nutrients, like nitrate, are readily flushed into the watershed if a big rain hits soon after application.

Dr. Earth Fish Bone Meal
Miracle Gro Bone Meal
Southern Ag Kelp Fertilizer

How does this relate to regenerative agriculture?

Prior to the 19th century, agriculture relied on organic fertilizers and the natural nutrient cycle to provide nutrition for their crops and pastures. This has changed dramatically over the past 150 years, as global agriculture uses over 215 million tons of synthetic fertilizers each year.4 Experts estimate that just under half of the world’s population depend on synthetic fertilizer production to survive.5 In my opinion, we should respect this outcome of the Industrial Revolution. I understand some of the implications this industrialization has had on the planet, the climate and its resource base. However, I believe each human life is a gift and agricultural advancement has allowed us to support more human life than ever before. Not mention that most modern humans live in areas of food security and don’t have to spend hours a day growing their own food to keep their families alive, allowing them to pursue other interests. That’s largely a good thing. To truly shift to a more regenerative system, I believe that we must approach the current system with some form of gratitude, acknowledging its advances and successes, and work with what it does well.


With that said, regenerative agriculture is a much better use of fertilizer for producers, for the ecosystem and for the future of humanity. Data show that around two-thirds of inorganic N and more than half of synthetic P is not taken up by the crop the year it’s applied.6 Much of it can be washed away into streams and rivers if there are no growing plants to hold it on the land. It’s the same basic concept as “reduce, reuse, recycle.” Think about it: How does the great Amazon Rain Forest produce so much year after year without one pound of synthetic fertilizer application? The answer is efficient nutrient cycling primarily done by microscopic life. Regenerative farmers and ranchers across the world are learning how to harness the power of natural nutrient cycling to their advantage. We call this “biomimicry”. Imitation is, after all, the greatest form of flattery, and what better system to imitate than one that has had millennia to improve itself.


We are only at the genesis of learning how efficiently nutrients can be kept on the land and cycled through practices like cover cropping and rotational grazing. It’s a truly exciting time to be in agriculture. Maybe one day soon the majority of producers will “farm naked” like Rick Clark. It’s up to us to find out.

For more information on  individual nutrients, their importance and how they cycle, head over to the Plant Nutrition article in the Plant Fundamentals section.