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Natural Sources of Nitrogen for Sweet Corn


Q. I have a question about urea. I understand what it is in its natural form, and I understand its effect on plants. I have been struggling to grow sweet corn the last few years and I'm sure it is the low nitrogen content of my soil. I have been adding compost, manure and leaf mulch but I just can't seem to get enough nitrogen to the corn. I have been thinking of also using urea, but am concerned that it's not as "organic" as the suppliers would like you to believe. I don't want any chemicals in my garden. Is urea safe? If not, is there another source of nitrogen I can use on my food craving corn?

(By the way, I searched for urea in your 'A to Z Answers' and you don't even have the letter U listed! Nor was there any listing for nitrogen sources under the letter N). Thanks,

---Dave in Carlisle, Pa

A. You gave up too quickly and/or were 'too clever by half'; the info you're after was there under…wait for it: Sweet Corn! (Your true topic.)

Now, you raise some very interesting points about "Urea". When I saw your question, my first thought was that urea is about as far from organic as you can get. After all, modern urea (used, as you note, as a high nitrogen fertilizer), is a synthetic chemical created in the 1820s using silver cyanide and ammonium chloride; a pretty nasty combination to these oh-so organic ears. But a little research learned me that urea was originally the name for the nitrogen content in urine. (The creation of the synthetic version created quite a sensation in the scientific world, as it was the first time that something that naturally occurred in the human body was duplicated in a lab.)

Anyway, today's urea is that inorganic, artificially created compound. Used in agriculture, it damages soil life and water supplies and contributes to massive losses of topsoil. And unfortunately, some very close chemical cousins (like Ammonium Nitrate) find their way outside of agriculture all too often to be used as weapons of choice for terrorists: from the American losers who blew up the Oklahoma Federal Building in 1990 to the enemy forces still attacking our troops with 'Improvised Explosive Devices'. All that carnage, facilitated by commercially available fertilizers that so-called 'conventional farmers' use to grow corn.

Anyway, corn IS a heavy feeder that, like lawn grasses, craves the nitrogen you feel your soil is lacking. One of the best organic ways to get lots of nitrogen is the corn gluten meal we always recommend as a lawn food—you just have to be aware that corn gluten meal also prevents the germination of all seeds—not just weed seeds. So to use it correctly, you'd first make up a weed-free seed bed (see our previous Question of the Week on the 'stale seed bed' technique, plant your corn seeds, water well and watch the little baby cornstalks come up. All seeds contain a good amount of plant food, so those babies will be fine for their first couple of weeks. After that, dust some corn gluten meal between the rows every couple of weeks. You'll feed your corn perfectly and prevent any late-blooming weed seeds from sprouting. (Now THAT's 'weed and feed'!)

Alternatives? As we mentioned in our last thrilling episode, some other natural sources of nitrogen have become kind of dicey in our Brave New World of so-called "Conventional agriculture". Composted horse manure (not fresh! Never use any kind of raw manure!) used to be a sweet corn fertilizer of choice. Then a new generation of persistent herbicides that survive the composting process came along and made horse manure a potentially dicey choice. If you have access to what you hope is good, clean horse manure, be sure to test it before use by trying to sprout pea seeds in it. Peas are exceptionally vulnerable to these herbicides, so if the peas come up and the plants look okay, the composted manure should be safe to use.

Composted chicken manure from a small flock that is tended by intelligent beings should also be safe—and chicken poop is even more nitrogen rich than horse. But manure from 'conventionally raised' chickens may contain arsenic. (Which makes being an unconventional farmer and gardener look better all the time.)

An interesting alternative is coffee grounds, which can't be used 'straight' as they're much too acidic, but they are the highest nitrogen kitchen waste we produce. And I love my fresh brewed morning coffee. Thus, an experiment that I am currently conducting.

I haven't normally grown sweet corn, as most of my garden area has been 'blessed' with abundant shade, and I've reserved the few really sunny spots for fruiting crops like tomatoes, peppers and my wife's peach trees. But last year's visit by Hurricane Sandy and the previous year's 'Halloween storm with no name' took out a lot of our trees, greatly increasing my sunshine potential.

So I have a bed of sweet corn growing this season that I initially fed with corn gluten meal (two big dustings), and then coffee grounds to which I've added ash from our wood stove in an attempt to level out the pH. I'm just fooling around, eyeballing and ballparking the amounts—but so far a couple of tablespoons of ash mixed well into each wet quart of grounds seems to be having the desired effect. I have big healthy stalks with lots of pollen grains on top and tons of silks to receive the pollen. And the ears seem to be filling out nicely…

So stay tuned; I'll be picking in a week or so and will announce how it tastes on an upcoming show!

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