About Nitrogen

NITROGEN KILLED THEM. All those poor dogs and cats that died recently from eating contaminated pet food--they died because of nitrogen. Not directly, of course. But because of a desire to increase the amount of nitrogen in dog and cat food. That was the reason that makers of pet-food ingredients in Asia added melamine, an inexpensive synthetic compound that happens to contain a lot of nitrogen, to their product. And that in turn was the contaminant that killed all those pets recently.

A column by science writer Natalie Angier in today's New York Times got me thinking about this connection, which is very relevant to us as gardeners because we use a lot of nitrogen. Nitrogen is the N in the N-P-K that adorns every bag of fertilizer we buy, whether synthetic or natural, denoting the presence of three nutrients that are vital for healthy plant growth.

As Angier explains, nitrogen is also vital to animal life, an essential building block of the proteins from which we animals are made. Nitrogen and protein are so closely linked that a quick way to test a product for protein content is to test for the presence of nitrogen. Unfortunately, it's possible to cheat on this test, boosting nitrogen content by adding an inexpensive high-nitrogen compound instead of a (more expensive) protein. That's what happened to the dogs and cats: The Asian makers of pet-food ingredients added melamine so that their products would test out as having a higher protein content than they really did.

Although nitrogen is common in the air, it cannot be used in this form by animals or even by most plants. To be useful for life, nitrogen must be fixed, another term familiar to most gardeners. Most of us are aware that certain plants, especially those in the legume family, are capable of converting nitrogen to usable form. This is why it's a good idea to plant beans (nitrogen-fixing legumes) next to your tomatoes (heavy users of nitrogen that can't fix the stuff for themselves). Another nitrogen source most gardeners know well is animal waste. (I don't know about you, but I did not know--until Angier told me--that rain falling on a garden after a thunderstorm also contains a lot of usable nitrogen, which has been fixed by the electricity in lightning.)

Most of us also know that nitrogen must be used sparingly in the garden. Too much nitrogen, and plants turn black and "burn." That's why we're careful about how much artificial fertilizer we use, if we use it at all, and why natural fertilizers such as composted manure are much safer (and better in a number of other ways) to use. Even fresh manure can be too "hot" for the garden.

Many of us even realize that nitrogen can cause problems when it reaches waterways: Dangerous algal "blooms" are often caused because runoff containing fertilizer, leaks from sewage systems, or animal waste increase the amount of nitrogen and other nutrients in a body of water, feeding the algae in the water. That's another reason why it's such a good idea to use fertilizers, such as composted manure, that do not have a super-high nutrient content and will release their ingredients slowly rather than all at once.

Less well known is that some non-leguminous native plants are nitrogen fixing. Alders, for example, are widely thought of as weeds because they readily spring up on abandoned farmland, in clearcuts, and any other land that has been harshly treated by humans. At one time it was customary to cut them down or treat them with herbicides as quickly as possible. Then in 1990, research conducted on a plantation on Vancouver Island in Canada found that Douglas fir trees grew two and a half times better when they were grown together with the locally native alder. The alders were adding nitrogen to the soil, and this in turn was encouraging the growth of surrounding trees. More than 15 years later, people who (like me) are trying to restore large tracts of land often look forward to the arrival of alder, seeing this as the first step in a natural process of ecological restoration.

The relationship between alder and other plants is an example of Nature's wisdom: A plant that can thrive on harshly treated soil also has the ability to improve that soil, making it ready for other plants. The more we learn about Nature, the more we discover that all sorts of plants and animals human beings disparage actually have important roles to play. The fact that our first impulse was to cut the alders down is an example of why humans should pay more attention to the lessons Nature has to teach. The fact that we didn't even begin to understand this simple relationship until 1990 shows us how much we have left to learn.

What does all this mean for the gardener?

I think one lesson Nature is teaching us is that more is not better. In our gardens, this lesson should lead us to avoid solutions that may seem quick and easy at first, such as using potent artificial fertilizers, in favor of slower acting, more natural solutions that may not give overnight results but will work far better and will do far less harm in the long term. As my mother always used to tell me, "Slow and steady wins the race."

Another lesson is that we need to trustNature a lot more than we are inclined to: If alders tend to grow on badly treated soil, for instance, we need not jump to the conclusion that Nature has made a mistake. On the contrary, the best response is usually to be patient, to give Nature the benefit of the doubt, to try to learn more about what she is up to, and to try to work with Nature rather than against her.

Mother (both of them) knows best.

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