If you read a number of web sites, especially organic gardening ones, you quickly realize that there are two basic kinds of fertilizer. There is the ‘synthetic fertilizer’ which you buy in bags. This fertilizer is clearly BAD! Then there is the good stuff; organic fertilizer.
What is the real difference between organic fertilizer and synthetic fertilizer? Is there a difference? The answer may surprise you.
What is Fertilizer?
Wikipedia defines fertilizer as any organic or inorganic material of natural or synthetic origin (other than liming material) that is added to a soil to supply one or more plant nutrients essential to the growth of plants. From a gardeners perspective, fertilizer may contain NPK and minor nutrients (sulfur, magnesium, iron etc). The NPK number is a short form for nitrogen, phosphorous and potassium.
Synthetic fertilizer is also called inorganic fertilizer or commercial fertilizer to differentiate it from organic fertilizer. This fertilizer is either mined from the ground or synthesized by man. It consists of granular material and comes in bags.
Any fertilizer that originates from an organic source is considered to be organic. Some examples include fish extracts, manure, and compost. It can be purchased in bags or bottles and can be ordered in bulk as trailer loads.
What Does the Plant Need?
To better understand the differences between fertilizers it is important to understand things from the plants point of view. What nutrients can a plant use? Can it distinguish between a synthetic and an organic source?
Plants get almost all nutrients through their roots. You can think of the outside wall of the root as having small holes or pores. These holes are used to let certain molecules into the root. The process is more complex than this, but it is not a bad analogy.
These holes are quite small and so only small molecules can get through them. Water molecules consisting of H2O are small enough and get into the root. Nitrate is also a small molecule, NO3, and it is also absorbed into the root. Other nutrients such as phosphorous, potassium, iron, magnesium etc are all small enough to enter the roots.
Large molecules like proteins, DNA, carbohydrates etc are huge in size compared to the nutrients. They just don’t fit through the holes. In fact most organic molecules fall into this category.Plants can’t use most organic molecules found in the soil! Almost all of the organic material in compost, manure etc is of little use to plants – they simply can’t get the molecules into the roots.
Large organic molecules do contain nitrogen, phosphorous, potassium, iron, for example, but in the organic form they are too big to get into the roots. For example, protein is a good source of iron, but because protein molecules are so big, plants can not use the iron contained in the protein.
Eventually these large organic molecules do break down and when they do, the small nutrient molecules are released, and then plants can use them. For a better understanding of this see Compost – What is Compost.
Plants need the small molecules in order to grow. One of the key nutrients, besides water, is nitrogen and plants usually get nitrogen in the form of a nitrate molecule.
Synthetic and Organic Nitrate Molecules
Let’s look at nitrate molecules in more detail. What is the difference between a nitrate molecule from a synthetic fertilizer and an organic fertilizer? The pictures below shows the two molecules.
Synthetic nitrate molecule Organic nitrate molecule
Can you see the difference??
There is no difference. A nitrate molecule from either source is exactly the same. More importantly plants can’t tell the difference either.
I’ll repeat the last sentence since it is one of the biggest gardening myths. There is absolutely no difference between a nitrate molecule from a synthetic source and a nitrate molecule from an organic source.
This last fact is hard for the pro organic movement to believe. How can they be the same when organic is so much better?? The fact is that when it comes to providing nutrients for the plants, organic is NOT better. It is exactly the same as a synthetic source.
Is Organic Fertilizer Better?
From a strictly chemical nutrient point of view organic is not better, nor is it worse than synthetic. It is exactly the same. However we can look at things from a different perspective and then we will find that organic is better- see Organic Fertilizer – What is it’s Real Value?, for more details.