Rain vs. Irrigation
Edna M Weigel (firstname.lastname@example.org)
Wed, 8 Sep 1999 15:28:18 -0700
What I'm missing in the previous discussions of this subject (and
my computer time has been limited so I may have overlooked something by
scanning too fast) is the fact that rain water (as opposed to ground
water and surface runoff water) is nearly free of salts. At least in the
arid part of Arizona where I live, the conventional advice is to water
deeply every third or fourth time to wash the salts below root level. I
don't do that, but then I don't add conventional fertilizer or more than
a very little manure and thus have less salt build up in my soil than I
otherwise would have. Conventional fertilizing (as well as excessive
manure) adds to the problem by adding excess salts (I'm not talking about
just sodium chloride here, but salts such as ammonium nitrate, super
phosphate, etc.) which change the osmotic pressure in the soil to make it
harder for the plants to take up the water that is present.
While I agree that the nitrogen and humidity most likely have a
positive effect, I think the relative purity of rain water makes it more
effectively absorbed by plants than water that has been saturated with
whatever salts it picks up as it percolates through the ground on its way
to the water table.
Happy growing, Edna
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