ARE FERTILIZERS BAD FOR THE SOIL?
Farmers and gardeners have been taught that fertilizers enrich the soil, but chemical fertilizers can harm the soil by diminishing the soil organic matter.
“In conventional agriculture, for the last 80 years, we've been over using synthetic and soluble nitrogen fertilizers and underutilizing insoluble organic matter fertilizers. Organic fertilizers include manure and crop residue. There's a certain efficiency to the natural processes of organic matter breakdown. It's like a drip filter of nutrients.”
—Dr. David R. Montgomery
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From a conversation with geologist and soil scientist David R. Montgomery, PhD of the University of Washington. For the entire interview, please click on the link below.
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HART HAGAN: Are fertilizers bad for the soil?
DAVID MONTGOMERY: It's an interesting question that's got a nuanced answer in the sense that, in the broad definition of the fertilizer, it actually helps the soil. For example, the leaves that trees shed in the fall are fertilizer for the soil that they fall on, because they then rot and they produce elements that can get back into biological cycling.
Where we get into trouble with fertilizers is that the over application of synthetic nitrogen fertilizers in particular is something that is known to accelerate the breakdown of soil organic matter. You get a little burst of productivity not just from the fertilizer, but also the stimulation of the microbes that the fertilizers impact. That can draw down the batteries of the soil and in effect draw down the organic matter content. It can also can change the soil community structure.
If you look at the life in the soil, if you have soil that's rich in organic matter--versus the soil that's poor in organic matter but gets a lot of fertilizer--you can grow a large amounts of crops in both, but you'll have very different communities of life in the soil, which then impacts how things like mineral micronutrients get into plants or the way that the plants tee up their physiological systems to produce things known as phytochemicals, plant made chemicals, which plants make for their own protection and communication. Phytochemicals in turn have an influence on human health when they get into our bodies.
So if you think of fertilizers in a very general sense, that's kind of agnostic in terms of, are they good or bad for the soil? It depends what kind of fertilizer you're using, how much, how often, in what ways.
In conventional agriculture, for the last 80 years, we've been over using synthetic and soluble nitrogen fertilizers and underutilizing insoluble organic matter fertilizers. Certain traditional fertilizers, like manure, crop residue--those kinds of organic inputs--are fertilizers, but they have very different characteristics.
One of the downsides of synthetic nitrogen fertilizers, the very soluble ones, is that you'd think it would be good to make fertilizer soluble so the plants will take it up because you want the fertilizer to get into the plant. But that also means that if it rains right after you've applied your fertilizers, it’s soluble, so it goes where the water goes.
So the fertilizer goes down to the water table to somebody's water well, or off to a stream to pollute the rivers and streams and ultimately down the Mississippi River to the Gulf of Mexico.
Fully half of the nitrogen that we apply in synthetic fertilizers in conventional agriculture never makes it into a crop so it never makes it into a person (as food). It ends up as off farm water pollution.
But there's a certain efficiency to the natural processes of organic matter breakdown. It's like a drip filter of nutrients. It's a different way to think about a fertilizer. But what we've been doing is over plowing, and we've been overusing soluble fertilizers in agriculture for quite some time.
This has impacted soil organic matter and life in the soil in ways that have impacted what our crops are able to take up. That impacts not only their health but impacts what gets into our food as well.