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The "perfect" lawn and other side effects

By Al Cooke
Posted Monday, November 23, 2009


Pittsboro, NC - Like Carol Taylor, I also noticed some non-sequiturs in Tim Keim's comments in his Chapel Hill News article on "The Perfect Suburban Lawn". I understand that Tim has the best of intentions - protecting the natural world on which we all depend - and I salute your objectives. You've just made a few conclusions that don't necessarily follow from your observations.

As Carol suggests, when you get a good rain, earthworms will do the same things humans do during a flood. You saw it on TV when New Orleans flooded; people headed for the roof. Earthworms likewise leave the flooded soil regardless of whether fertilizer has been used. The fact that they are there and able to emerge suggests that the lawn treatments have not been fatal to them. Possibly their death is the result of their high sensitivity to the ultraviolet light they encounter when they leave the flooded soil and have to wait for the waters to recede.

It's OK if you want to bash Monsanto and other chemical companies. And I can't say absolutely that glyphosate (the active ingredient in Roundup) is not toxic to fish or other organisms, because I have a scientific background and know that we can't prove a negative. A 16th century scientist noted that "the dose makes the poison." As suggested above, even water can be fatal to humans. But glyphosate is "practically nontoxic" to fish to the point that it is legitimately used in certain aquatic herbicides for control of aquatic weeds that that create problems such as clogging irrigation intakes. And those applications are seldom or never followed by fish kills.

There are other things that can cause fish kills, and that brings me to the idea of using corn gluten meal to prevent weeds sprouting. Those who did most of the early research on this material (Dr. Nick Christians and his graduate students at Iowa State) found that the amount of material necessary to get weed control includes about twice the highest rate of nitrogen recommended as a best management practice for most crops including lawns. The nitrogen in corn gluten comes in the form of protein which promptly breaks down first to amino acids then to the same ammonium nitrate that is in synthetic fertilizers, the only form of nitrogen that we know for sure that plants can absorb and use. This same nitrogen, unlike glyphosate, is a significant and documented problem in waters of North Carolina as Tim correctly noted. When nitrogen causes eutrophication, the dead fish don't much care whether it came from a bag of corn gluten meal or a bag of 10-10-10. It's fine to use the corn gluten if you use it with care.

Just please be aware that in the humid southeast researchers find that it is effective for a far shorter time than they found in Iowa. It breaks down more quickly ending its effectiveness at weed control and releasing that load of nitrogen. If you expect continued weed control, you may need to repeat the application contributing far more nitrogen than is good either for your lawn or for our water. And like everything else that goes on in your soil, the dynamics are affected by things like temperature and availability of water and oxygen.

We all need to be careful out there and think about what we're doing. Everything is connected to everything else. It's not nearly as simple as organic or synthetic, and maybe that's a good thing. But with the best of intentions, you can still have negative environmental impacts.

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The "perfect" lawn and other side effects

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