Why Do They Do That? Farmers Applying Chemicals

There are lots of questions a consumer might have about chemicals. Why are farmers putting chemicals on their fields? What chemicals are farmers putting on their fields? What do the chemicals do? Are there chemicals in our food? Are there harmful chemicals in our food?

First, though, we need to answer a big question – what is a chemical?

One good definition of a chemical might be a form of matter having constant chemical composition and characteristic properties. That is to say, you cannot break this substance down without breaking chemical bonds.

A chemical bond is a strong association between two different atoms. Remember that all matter is made of atoms – for a long time, science thought this was the smallest thing we could break matter into, but then they found protons, neutrons, electrons and other tiny, tiny stuff inside the atom.

In your high school science classroom there was likely a Periodic Table of Elements. On that table, things like atomic weight and atomic mass are mentioned. Each of these elements has a different type of atom that makes it up. To brush up on atoms, check out this Crash Course video.

In chemistry, we look at the characteristics of these atoms and elements. The way they interact, bond, and perform is chemistry.

The thing that trips us up is really the colloquial way the word “chemical” has been used. When we think chemical, we think of a steaming beaker full of thick, bubbling, lime green acid, right? But really, everything is a chemical. Water is a chemical (H2O), sugar is a chemical (C6H12O6), caffeine is a chemical (C8H10N4O2), and so is salt (NaCl)! We are even made of chemicals! Our DNA is made of four different nitrogenous bases (adenine, guanine, thymine, and cytosine) – each a different chemical.


Photo from Google

Therefore, if you ever see or hear someone try to sell you something that is “chemical free”, you can know it is a marketing gimmick. In fact, the FDA forbids the phrase “chemical free” from being used on meat and poultry labels, because that is an impossibility. Rest assured, you have never purchased anything that was “chemical free”.

However, that still may not answer your questions. You may still wonder what is being used to produce food. Is it safe? How much is used? How is it used? Though there are many different individual products, let’s try to break down purposes and highlight a few representative chemicals in each category.

What chemicals are farmers putting on their fields?

One umbrella term for many products is pesticide. We’ve written a previous blog post about pesticides that you can find here, but we will summarize a little bit here.

Chemical inputs in agriculture

Pesticide is a term that includes many different things. A pesticide is something that is used to control some kind of pest. These pests can be weeds, insects, fungi, or even rodents. Because each of these things would be formulated very differently, it wouldn’t be fair to generalize much more over these lines.

Herbicides (a pesticide used to kill weeds) likely get the most press of the pesticides. To get a rundown on what herbicides are, check out this blog. Farmers use herbicides to kill weeds for a couple different reasons. First, weeds use up water, space, and nutrients that their crops need. This adds extra competition and makes the crops less productive. By eliminating weeds, plants grow better and produce more food. Second, the alternative to using herbicides to kill weeds is either hand-pulling weeds or using tillage. Hand-pulling weeds is likely the most effective but raises humanitarian issues regarding working conditions and the like. Tillage can be effective as weed control but degrades soil structure and leaves the earth susceptible to erosion, which can also contribute to water quality issues.

Insecticides (a pesticide used to kill insects) are used to remove harmful insects from a crop field. For example, this year the thistle caterpillar has been wreaking havoc on soybean fields in the state. When this caterpillar builds its chrysalis, it folds the soybean leaf over itself, and eats its way out after this stage. This means the leaves of the plant are all but destroyed, making it very difficult for the plant to photosynthesize. If the pressure of this insect in a field reaches the economic threshold (the threshold by which it will cost less to use an insecticide than it will cost in crop loss), the farmer will likely choose to spray the field to kill these insects.

Fungicides (a pesticide used to kill fungus) are used to help mitigate disease. Sometimes plants can be susceptible to different kinds of fungus growth that can hurt the plant and even kill it if left long enough. Disease is a major contributor of crop loss globally, with fungi being the number one cause of crop loss. Since fungi growth is dependent on moisture and temperature, this can be difficult to control in a farm field without applying some type of chemical, whether that be organic or synthetic.

Outside of pesticides, farmers may also apply soil amendments. These things help keep the soil healthy. They can range from limestone (calcium hydroxide, in a powder and called “ag lime“) to a range of fertilizers.

Fertilizers help replenish nutrients in the soil so that it remains productive and plants can continue to grow in the same place. Keeping soil productive is a major piece of environmental sustainability. There are many essential nutrients that plants need to be healthy. Therefore, fertilizers can vary greatly depending on nutrient content, geographic location, crops planted, and many other factors. Fertilizers can come from many different sources, from manure from livestock and compost (both organic sources) to anhydrous ammonia (derived from atmospheric nitrogen using the Haber-Bosch process).


An example of some fertilizer types from NEW Coop. Underneath the bold name are three numbers. These indicate the amount of nitrogen, phosphorus, and potassium in the total fertilizer, respectively.

All of these types of inputs have organic and synthetic counterparts. Organic farmers can apply pesticides as can conventional farmers. However, the terms organic and synthetic do not include how effective or toxic to humans the product is. Some products may take a long time to break down and others break down very quickly. Some are much more toxic to humans than others. Some are much more effective and therefore farmers don’t need to apply as much of them. These characteristics are much more important to the safety of the farmer and the landscape than how they were derived.

Are chemicals used in food production safe?

This is a great and very important question. Safe food production is important because we all depend on safe food, and we need to care about the safety of those working in food production. So, is it safe?


Some examples of bulk storage of crop inputs. These inputs are housed at a cooperative. A farmer may hire the co-op to use their own equipment and materials to spray instead of investing in all of the equipment themselves.

Inputs applied to farm fields are regulated. The Environmental Protection Agency leads the charge in the U.S. for overseeing pesticide regulation. They work with the Food and Drug Administration and the U.S. Department of Agriculture to ensure pesticides are being used in a way that maintains a safe food supply. They also work with the Bureau of Land Management and the U.S. Fish and Wildlife Service to ensure the environment remains safe. 

When commercial crop inputs are purchased, they come with a product label. This label can be dozens of pages long (here’s a 58-page long glyphosate label), and acts more like an instruction manual. Many things are dictated in these labels, including when to spray, how much to spray, and how to store and dispose of the material. Not following the label is illegal. However, these inputs do cost money, so it’s not in a farmer’s best interest to use more than necessary, even if it was legal.

These labels are created to ensure safety. Farmers and agronomists using these inputs are educated and trained on how to use everything with thoughtfulness, foresight, and attention.

How are chemicals applied on farms?

Though this can vary, most crop inputs are sprayed on fields using sprayer implements or sprayer planes. However, most of the liquid being sprayed on a field is water. For example, when glyphosate is applied to one acre of land (about the size of a football field), only 32 ounces of the product is used. That’s just a couple of pop cans full! The rest of the tank in the spraying implement is water. The water helps carry the product across the field.

2015-08-13 09.42.19

This sprayer’s boom can fold and unfold, and be raised and lowered. The high cab and skinny tires accommodate row crops better than a traditional tractor.

Some products may use more or less depending on the effectiveness of the product. This application rate is specified in the label, along with sprayer nozzle type, and weather considerations.

Some inputs are solids, meaning spraying doesn’t work as well. For example, ag lime is broken down limestone, which cannot be sprayed. Instead, a tractor may pull a spreader across the field to scatter the lime evenly.

In places where agricultural fields are much smaller, equipment can be much different. There, you might find farmers with backpack style sprayers that hand-spray their crops for insects and fungicides that hurt their crops.


Chemical inputs can be complicated. There are a host of different products and uses that dictate things like dosage, toxicity, half-life, and others. However, it’s important that we evaluate products more by these characteristics than by how they were derived. With the decrease in arable land and increase in population, it is important that we have as many tools in our toolbox as possible to help create solutions that maintain our land quality, food quality, and our safety.


2 thoughts on “Why Do They Do That? Farmers Applying Chemicals

  1. Pingback: Unique Farming Challenges – Armadillos? | Iowa Agriculture Literacy

  2. Pingback: Unique Farming Challenges – Armadillos? – Technology

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