I recently read that only about half of fertilizer that is applied actually makes it to a plant. This means that the remaining half is lost. It is lost in waterways, volatilization (it escapes into the air), and is tied up or made unavailable by the soil. Now, I’m sure that every soil and situation is different, but thinking about this statistic made me realize that when fertilizer is applied a lot of it is for naught. Not only does this lost fertilizer fail to help our pastures and crops, it actually hurts our waterways and, at times, even our own drinking water supply. The fact that so much fertilizer is lost should give us pause to think about not only the environmental consequences of fertilizer applications but also the economic return on applying fertilizer.
In our pasture that is a Diverse Native Grassland, we don’t apply any fertilizer rather we count on the healthy soil and its microbiology to “unlock” the nutrients for our plants. Let’s take for instance nitrogen, a commonly applied fertilizer. We feel that it is not necessary to use it in our grassland. Even though we aren’t applying nitrogen fertilizer, we acknowledge that it is terribly important nutrient to plants. It is part of chlorophyll, which is what makes plants green; this makes it a key component in the conversion of sunlight into plant sugars or “food”. It also has many other functions. So, if it is important to have nitrogen and we aren’t adding it in fertilizer, how are we getting it to our plants?
First, nitrogen is already in the plant material that is growing, so if we can just recycle it, the new plants can reuse this very same nitrogen. In order for this to happen, the old, dead plant material is consumed by bacteria, fungi, and other soil microbes, and these organisms make it available to the new plants.
Another source of natural nitrogen in our pasture is through nitrogen-fixing-bacteria. These microbes provide nitrogen to plants in exchange for the plant providing them with food. The most well-known example is legume plants and Rhizobium bacteria. However, other plants such Eastern Gama Grass (Tripsacum dactyloides) and Ceanothus species also have microbial associations that provide nitrogen for plants.
The last reason that we don’t use nitrogen fertilizer is that it often deceases the diversity of plants, which decreases the health of the soil and its microbes, which in turn decreases the recycling of the nitrogen in the soil. So, in effect, fertilizer hurts the soil’s nitrogen recycling program. Fertilizer can also cause the symbiotic plant and nitrogen-fixing-bacteria relationships to not happen or not produce as much of the natural nitrogen fertilizer for the plant.
In summary, the natural grassland ecosystems have a system for recycling and making their own “fertilizer”. The addition of nitrogen fertilizer not only doesn’t take advantage of this system, but it also throws it off balance and messes it up.