Fertilizer Basics: Chemical

It's been 4 or 5 years since I mentioned fertilizer chemistry, and with spring around the corner a lot of farmers and gardeners are getting ready to plant this year's crop. The science of soil chemistry is a college-level subject, but I'll try to cover the basics and give you a base to build upon.

I'm not going to get into which fertilizer you will need for each crop or condition; that's an industry in itself known as Agronomy and I don't have the space to cover everything here. Do your research on what you're going to grow and take notes on what to look for that indicates possible nutrient deficiency. Unfortunately, without access to a lab and soil sample, you'll have to plan your fertilizer use by how the previous year's crop did.

Fertilizer is anything you add to the soil to provide nutrients that your plants need to grow and yield. A properly fertilized filed or garden will produce more and better food, so the cost of the fertilizer is usually offset by the increase in yield. This applies even if you're growing flowers: a properly fed row of flowers will give you more and bigger blooms and leaves, which is handy if you're growing herbs. Trees can also benefit from being fed the right things, especially when they are transplanted or young, as getting a good start means a longer life and a sturdier tree. I'll look at commercial (chemical) fertilizers in this post and cover manures and organics later.

Chemistry Ahead!

Plants require various chemicals to grow and produce fruit. They can pull carbon, hydrogen, and oxygen from the air and water around them, but they also need two classes of nutrients in smaller quantities.

Macro-nutrients are needed in fairly large amounts and are used in the production of the building blocks of life like carbohydrates and proteins.

• Nitrogen (N): Essential for protein synthesis.
• Phosphorus (P): Used to create new cells for growth and allow stored food energy to be converted to chemical energy.
• Potassium (K): Helps maintain water balance and transpiration in the leaves of plants.
• Sulfur (S): Part of many amino acids, the building blocks of proteins.
• Calcium (Ca): An important part of nutrient transport through a plant and used in enzyme production.
• Magnesium (Mg): Used in the photosynthesis of sunlight to carbohydrates.

Micro-nutrients are trace elements that are required in much smaller doses for optimal health, like the vitamins we give children. 

• Zinc (Zn): Mostly used by the plant in growth regulation and protein production, one of the main limiting factors in plant yield.
• Iron (Fe): Used in enzymes and helps make other nutrients available to the plant. Fe is also critical in the production of lignin, which is part of the plant stem or stalk.
• Manganese (Mn): Makes S and P more available to the plant and is also used in enzyme production.
• Boron (B): An important part of building and maintaining cell walls within the plant.
• Chlorine (Cl): Important for many energy-transfer reactions within the plant, this one is rarely in short supply.
• Copper (Cu): Activates many enzymes and is used in protein production.
• Molybdenum (Mo): Used in the root systems to help bacteria bind N into a form that plants can use.

Commercial fertilizer is usually marked with a series of numbers separated by hyphens. The macro-nutrient chemicals are listed in the order of N-P-K and represent the percentage of each available in that fertilizer. These are the three numbers you will see on most bags of fertilizer in the garden shops and big-box stores. Urea is a common form of N, and it will be marked 46-0-0.

Some specialty fertilizers will have more than three numbers, with S and Zn being next in the list, so you may see something like 12-40-0-10-1 which tells you it has 12% N, 40% P, 0% K, 10% S, and 1% Zn. Ammonium Sulfate, a common fertilizer used to lower the pH of soil, would be designated 21-0-0-24 (sometimes 21-0-0-24S). Boron, Iron, and the others are usually designated with their chemical symbols.

Commercial fertilizers are heavily regulated, I have inspectors from the state come by and grab samples of what we sell every few months. The lab tests ensure that we're not “cutting” the expensive stuff with cheaper chemicals to cheat our customers, and I get the results back to make sure my suppliers aren't cheating me. Certain chemicals lend themselves to, let's say, “recreational” uses and are further controlled by various government agencies, and a certain monster that I will not name blew up most of a federal building with a rental truck full of fertilizer-based explosives resulting in that form of fertilizer no longer being on the market.

The meth labs used to steal anhydrous ammonia (NH3) for one of the steps in their recipe, so we had to have locks on every single valve on every single tank that holds it. The cartels in Mexico can make meth in bulk and ship it cheaper than the idiots can make it locally, so we've seen a huge drop-off in NH3 thefts. I used to get Sulfur in 2000 pound bags, but since a person can use it to make black powder the BATFE has made it a paperwork nightmare today.

Be careful of what you stockpile; if you ever end up in the news, some things can be reported as “bomb-making materials” or “drug-making chemicals”.

With the distinct possibility of disruption of  the delivery of food (and other goods), growing some of your own food is always a good thing to try. If nothing else, you'll have fresh food that you know you can trust.