Inorganic fertilizer and earthworms

oakridge2January 29, 2008

I have heard that adding inorganic fertilizer to soil has negetative effects on earthworms. Based on my experience I question this.

I am not an "organic gardener". I do slow compost and add lots of organic material to my garden every year. I do not use pesticides, but do use inorganic fertilizers.

I have a sweet corn patch that is 15x15 ft. that I have added 10 lbs of 20-10-10 every spring for the last 4 years. The fertilizer is fast release from the local farmers Co-op. If you calculate the application rate for an area this size you will realize that it is an extremely high rate.

My sweet corn does great every year, large robust plants, huge ears of corn. My soil is full of earthworms (most of them non-native of course). I have not noticed a decline in the worms in 4 years of adding inorganic fertilizer at these rates. Isn't the salt flush from the fertilizer supposed to repel the worms? I do not see it. Can anybody provide me some scientific data on this topic?

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Hi Oakridge2,

I don't claim to be anything approaching an expert on worms and their tollerence for chemical salts, so sorry i can't help you with any scientific data, but you own observations over four years pretty much give you your answer, i would have thought.

I think it's more of a case of killing/depleteing the beneficial microbial life in the soil, rather than the worms. Chemical ferts can and do harm this 'microherd, although chemicals will happilly feed your crops year after year, it is also slowly and steadily creating havoc with the quality of the soil, and ultimately the taste and quality of the crops themselves.


    Bookmark   January 30, 2008 at 4:51AM
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Earthworms, and the other members of the Soil Food Web, need organic matter as a food source, so as long as you add organic matter to your soil they will be there, being slowly poisoned but still there. 10 pounds of a synthetic fertilizer spread over that area is not a lot, it is probably unnecessary but its not all that much. It is the dose, 20 pounds of the same thing spread over the same area might be too much.
What does a good, reliable soil test say about your soils need for this fertilzer? Are you spending money you do not need to doing something unnecessary?

    Bookmark   January 30, 2008 at 6:12AM
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Thanks for the replys. I would still like to see some scientific data supporting the theory that inorganic fertilizer harms worms or the microherd.

Kimmsr, I have not had my soil tested, would love to if it didn't cost to much. I know that corn is a heavy nitrogen feeder, thus the fertilizer application.

    Bookmark   January 31, 2008 at 7:49PM
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A soil test in Michigan for P. K. Ca, Mg, CEC, pH, the basics is $12.00 per sample while the price in Wisconsin, according to a friend there is $13.00. Not terribly expensive especially since it can save you much more in unnecessary fertilzer cost.

    Bookmark   February 1, 2008 at 7:23AM
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Thanks for the information Kimmsr, I am going to get a soil test done this spring.

    Bookmark   February 3, 2008 at 11:33AM
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david52 Zone 6

I have a neighbor who collects night crawlers and worms for the fishing trade, and he tells me that it takes a few months, after fertilizing a lawn with standard fertilizers, for the worms to "come back". I suppose he knows what he's talking about.

    Bookmark   February 3, 2008 at 4:32PM
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frank1965(z8 NWLouisiana)

I too question the negative effect of syn fert on worms. My long term potted plants on my deck are full of the fat buggers even after using slow release fert a couple times a year. Even the occasional dose of the dreaded miracle grow doesn't seem to deter them. I could only hope it would harm them since they break the mix down and impede drainage- wish they would stay in the garden where they belong.

    Bookmark   February 7, 2008 at 11:25PM
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lou_midlothian_tx(z8 DFW, Tx)

Go to soil food web website. They have loads of studies to prove that synthetic chemicals of all kinds have negative effect on soil biology.

    Bookmark   February 11, 2008 at 10:37PM
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You can find Dr. Ingham's Soil Food Web Primer through the link below.

Here is a link that might be useful: Soil Food Web Primer

    Bookmark   February 12, 2008 at 6:45AM
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lou_midlothian_tx(z8 DFW, Tx)

More of Dr. Ingham's stuff. Soil Food Web Primer and this one are probably the best two ones for anyone to read when starting organic programs. Far too many people jump in without having a clue on how soil biology truly works...

Here is a link that might be useful: Benefits of a Healthy Food Web

    Bookmark   February 12, 2008 at 9:28AM
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I use commercial fert in small amounts as needed and I also use a lot of green manures and composted materials. I have lots of worms. Which also dispells the theory that roto tiling destroys the worm count.

I have a friend who is heavilly into chemical farming, he plows down about 500 lbs of trip 19 per acre and sidedresses with pure N, and he has plenty of worms in his better soils. Some of his fields are very low to barren of organic matter , I never looked in these fields but I would bet the worm population is quite low. I wouldn't want to eat his produce tho.

I did use liquid N on my field corn a few years ago and that seemed to burn out the worms for a while.

    Bookmark   February 12, 2008 at 11:45AM
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If your soil is healthy, meaning an extremely active microherd, then they are breaking down most of the salts into more friendly organic waste products. The amount of the salts used, is the biggest determining factor, that and the amount of humus and organic matter available to the microherd. Don't get me wrong - salts are not healthy for the living soil, that much is proven, but in soil that is very rich in organic materials, with a vigorous microherd (present in some areas no matter what is being added to the soil), microbes and earthworms will still flourish. The earthworms will avoid the areas that are "weak" in microbes and gather in the areas that are rich in them. I base all of this off personal experience and opposite yard gardens that were fed differently for three years, but still enriched with the same amounts of compost, and organic materials. Good luck TiMo

    Bookmark   February 12, 2008 at 12:20PM
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