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From: chi9@quads.uchicago.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio,sci.chem
Subject: Re: How does soil stay fertile?
Keywords: soil fertility crop rotation
Message-ID: <1990Nov21.022345.6755@midway.uchicago.edu>
Date: 21 Nov 90 02:23:45 GMT
References: <1990Nov19.130439.9168@newcastle.ac.uk>
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Organization: Department of Biology at the University of Chicago
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In article <1990Nov19.130439.9168@newcastle.ac.uk>
william@lorien.newcastle.ac.uk (William Coyne) writes:
>In the past crop rotation without the use of artificial fertilizers
>was used to maintain the productivity of fields.
>
>How did this work?
>
>The soil requires various elements - nitrogen, sulphur, phosphorus. 
>Now the nitrogen can be obtained from the atmosphere by growing certain
>plants in the field(eg clover), but where do the other elements come
>from to replace those amounts of them used in the previous seasons?

	Well, you see, the sulfur comes from the sulfuric acid in acid rain,
and the phosphorus comes from the heavy application of organophosphate
pesticides. . .

	. . . All right, all right, just kidding.

	Seriously, I think that fertilizer-free soil maintainance schemes must
depend upon the application of manure and/or sewage sludge to return the
nutrients other than nitrogen (including micronutrients) to the soil, or else
depletion does occur eventually.

--
|   Lucius Chiaraviglio    |    Internet:  chi9@midway.uchicago.edu