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  • From: "Jeff Lowenfels" <jeff@gardener.com>
  • To: "gardenwriters-on-gardening" <gwl-g@lists.ibiblio.org>
  • Subject: Re: [gwl-g] soil pH
  • Date: Thu, 15 Apr 2004 09:53:53 -0800

Making some progress; thanks Lon and northern Jeff,
Lon, while I will check the literature, isn't it fair to assume if fungi
can do something to the soil in the forest, they can do the same thing
in the home landscape if the conditions and resources were the same?
<<<Jeff, you talk about the nutrient exchange in some cases taking the pH
up.  Isn't much of that nutrient exchange performed by mycorrhizal
fungi?>>
 
First, the fungi only bring nutrients to the plant roots. They still have to get into the root (passive, active methods of transport etc). Mychorrhizal fungi are great at bringing water and phosphorus to the rizoshpere. The actual exchange takes place when nematodes and protozoa eat the fungi and bacteria and poop out the excess nitrogen etc.
 
 
<< Therefore, if the root zone has a healthy population of root
fungi, the plant is in a better position to influence the pH in its root
zone than a plant with a small or inadequate population of root fungi? >>>
 
With fewer fungi there is less nutrient cycling going on as per the nematode, protozoa eating.  Less food, fewer critters
 
 
<<<Also Jeff - if some exchanges move the pH up, are there exchanges that
move the pH down? as in Lon' example of the forest fungi making alkaline
soil more acidic? >>
 
Oh yeah, anions are released when certain nutrients, mostly those in solution are adsorbed by roots.
 
<<I feel that there is a very important idea coming out of this
discussion. >>>
 
Don't discount the role of the bacteria and fungi in first buffering and eventually adjusting pH: The slime of bacteria (the same slime you feel in your mouth in the morning) has an alkaline pH and the organic acids released by fungi as they decay.  These organisms, incidentally, are attracted to the root zone by the exudates released by the plant itself. So, in a large sense, it is the plant that sets the pH....
 
Two other things and may be more than others want to know so we can take this off list, Jeff. First, compost has its own pH. Many gardeners think all compost has similar pH. Not so. You can make composts dominated by fungi and composts dominated by bacteria and they have different pHs.  Plants that are in the ground a long time prefer fungally dominated soils.
 
Second, putting compost on the soil around plants vs. putting mulches around plants needs to be examined. There are those who believe the energy used to make compost is somewhat wasted and that putting material down as mulch instead of in the compost pile results in much less carbon being "wasted." I use green mulches around annuals and vegetables and bulbs because these favor bacterial domination. I use brown mulches around trees, shrubs and perennials because this encourages fungal domination in the soil, 
 
Again, lots of this is short-hand and grossly simplified. Again, I am happy to take this off list.  However, I am a big believer that gardeners need to get out of the "Art" business and get with the "Science" of gardening. My readers here in Alaska sure seem to appreciate learning the science behind what they do.
 
Cheers,
 
Jeff Alaska



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