What is dirt, anyway?

It’s a mixture of things. Organic matter, silt, sand and clay. How much of each one is what causes each type of soil to look and feel the way it does.

What makes soil valuable is that it holds the nutrients that plants need to grow. Many of them are positively charged nutrients, those are called cations (pronounced cat-eye-ons).

Charged attractions are why a dry cleaning bag sticks to us. Our charge and the bag’s charge are complimentary. In soil, the nutrients loaded with positive charge seek a bond with the negative charges on any available surface area on the soil particles.

If the soil includes a lot of organic matter –which has a large surface area– then the dirt can hold more nutrients than if it’s mostly sand, which holds no charge, or clay, which has tiny particles and not much surface area. Put another way, we can stick more coins to a big balloon than a small one.

The surface area, combined with how strongly charged the soil is, will dictate how productive the soil is. That’s measured by what’s called a Cation Exchange Capacity, or CEC. The higher the CEC, the bigger and more efficient the nutrient supply is for a growing plant.

Much like the dry cleaning bag won’t stay clung to us forever, the calculation for a soil’s CEC includes the fact that the electrostatic bonds require energy, which will dissipate over time. In addition, a small layer of water prevents a perfect bind.

Despite these complicating factors farmers and agrologists work very hard in their efforts to try to balance the nutrients to the soil. If the nutrients can’t bind as well as possible, they get washed away and represent a wasted expense and lost time while also potentially contributing to waterway pollution. This is a lose-lose scenario for the farmer and the environment and great pains are taken to avoid it.

These factors help explain why some farmers can fertilize a lot at once, whereas others need to do more passes with lower amounts of nutrients. The farmer who’s doing multiple passes has soil that is sucking the cations through a smaller straw than the farmer with a high CEC.

It’s worth noting that there are also some nutrients that are negatively charged. Those are called anions (an-ions). Like the positive particles that lose their charge, those unbound nutrients are also easily washed away.

It’s also worth mentioning that there are a few places in the world where the soil is positively charged rather than negatively charged. That flips and reverses all of the same challenges. Rather than holding positive cations, those soils hold the negatively charged anions, like phosphate or sulfate.

The charges are in the top right corner of each element.

Of course, once the nutrients are in the soil, the plant needs to have a way to use them. To absorb cations, the plants produce positively charged hydrogen atoms that they can then exchange in order to take in the positively charged nutrients.

Hydrogen sits at the start of the Periodic Table of Elements with a charge of +1. This means a plant can trade hydrogen straight across for something like potassium, which has the same +1 charge. But if the plant wants something like iron, that’s a lot harder.

Iron has a +3 charge, so it represents a three-for-one exchange for the +1 hydrogen atoms. In addition, since the iron has that +3 charge the soil particle is actually held in place more tightly. It’s like us trying to pull a bigger magnet off a fridge, meaning it’s harder for the plant to loosen the nutrient so it can absorb it. These are the complex and often competing realities that make crop and food management extremely complex and difficult. Farming is very much a profession.

Obviously, targeting the individual chemicals using manure is essentially impossible. While modern fertilizer is often attacked, it not only creates 50% of the calories produced on Earth, but it does have the advantage of more targeted placement. Regardless of which form is wisest in which situations, the various forms of fertilizer are what have allowed farmers to turn weaker soils into productive sources of food for a growing population.

While fertilizer is often characterized by only its unavoidable and unintended consequences, it has been used since it was discovered for the very simple reason that it is society demands it –without it the 1970’s predictions of mass famines in the 1980’s and 90’s likely would have happened.

Using fertilizers definitely has –like all actions– negative as well as positive consequences. There are no perfect answers in something as complex as nature, so the job of the farmer is to balance our need for food with the consequences caused through growing it. Fertilizer is an expense, so the public can rest assured that no farmer has any interest in using any more of it than they need to. But to pretend we don’t need these valuable tools is to ignore all the lessons of nature.

Things grow because they get the right nutrients at the right time, and the professional farmers and the scientists who advise them are the ones that are maintaining that delicate balance. And that is yet another good reason for all of us to be grateful for the people that allow each of us to eat every single day of our lives.

See more from Scott McPherson.