[APWG] Ecosystem Restoration Site evaluation and analysis Soil and other site conditions Odor as a preliminary test Re: Smell soil to see if you have dead soil causing weeds?

[Wayne Tyson]

APWG: 

While I strongly smell a certain odor here, I must admit that I have used my nose in practice, but only to a limited degree and for limited and often preliminary way. Dogs and hogs have long been used to sniff out underground "fruiting bodies" of certain mycorrhizal fungi, and this might actually be possible to assess the presence or absence of certain symbionts, know of no studies in this regard. Anybody? 

The strong odor of anaerobic conditions can sometimes easily be detected by most human noses, and different compounds and elements certainly have distinct odors. There may be untapped potential here, but again, I am aware of no studies that verify the validity of smell tests. 

There is, however, plenty of folklore. I grew up on a stock-farm, and my father and others commonly sniffed soil to "judge" its quality. 

I don't doubt that there is a difference in the odor of "dead" versus living soils, particularly when organic matter is absent. But the absence or paucity of humus below the A-0 layer indicates that something more than a weed invasion is part of the soil's past. But again, context is everything, and that includes time. Soils lacking humus are usually either arid in the extreme or areas where the biological/living soil has been physically removed, not that "aliens" have taken it away. 

Such "dead" soils are more likely to support weeds than indigenous species because the site conditions and the genetics of the (weed) plants growing thereon match those conditions--in toto. 

There's more than soil, however, that minimizes the recolonization of disturbed sites by indigenous species. In time--perhaps a very long time--indigenous species usually do re-colonize such disturbed sites--when, and only when, all relevant conditions for their survival and reproduction are present. 

I have seen, for example, tiny pioneer populations of indigenous grasses gain a foothold in the midst of a large acreage of "dead" soils "full" (or so I thought at first) that had lain fallow (no livestock) for several years. Who knows what made this possible? Perhaps an animal had a seed caught in its fur, and perhaps another animal transported a mycorrhizal spore at the right place and time under the right conditions for their unification--who knows? But it happens. Once that plant is able to survive fatal predation and set seed, those seeds can then fall upon much more favorable conditions (e.g., presence of mycorrizal fungi), and the colony can then receive pollen from perhaps distant populations of the species. Time and distance can be major factors, among countless others. 

N-fixing bacteria may work for or against recolonization by indigenous species. Too much N almost always means weed dominance. 

The truth probably is that we still know far too little about the complex phenomena involved, but every effort to sniff them out is worth a try. However, we should never be so cocksure of our conclusions that we stop learning. 

WT
  ----- Original Message ----- 
  From: Robert Layton Beyfuss 
  To: craig at astreet.com ; apwg at lists.plantconservation.org ; craig at ecoseeds.com 
  Sent: Tuesday, September 24, 2013 3:56 PM
  Subject: Re: [APWG] Smell soil to see if you have dead soil causing weeds?


  I doubt if grant funders will provide restoration money based on smelling the soil. Dogs can be trained to smell certain cancers. Maybe we can hire them. Is there really any data regarding minimal nutrient thresholds for native plants? We have known for years that nitrogen is a tricky element to measure because it likes to quickly change forms from ammonia to nitrate, nitrite, etc . Any nitrogen measurement is a snapshot of a moment in time. Phosphorus is also turning out to be a tricky character due to mychorizzae. I have University lab soil test results from soils that list 0 pounds per acre of P, yet these soils are covered with healthy forests. 




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  From: APWG [apwg-bounces at lists.plantconservation.org] on behalf of craig at astreet.com [craig at astreet.com]
  Sent: Tuesday, September 24, 2013 4:24 PM
  To: apwg at lists.plantconservation.org; craig at ecoseeds.com
  Subject: [APWG] Smell soil to see if you have dead soil causing weeds?


  Dear All,

  I am going to suggest an even easier test to check for soil problems that can cause weed infestations--is to smell the soil?

  Where I have the worst weed problem at my site in Palo Alto, the Italian thistles and the medusa head grass, I noticed that when I dug up the soil for the soil nutrient tests on those sites, there was no visible organic matter below the weed thatch, and there was no smell to the soil.  The soil is dead, nobody microscopic like the fungi and yeasts, alive any more.

  Then if you go 20 feet away where there is no medusa head or Italian thistles, when you dig past the surface thatch, you can see visible organic matter, and if you breathe in, you can sniff that somebody is still home in that soil.  

  I am suggesting that along with soils being below the nutrient threshold for native seedling survival can cause weed infestations, that you can also have a case of weeds as symptoms of dead soil.  The weeds could be looked like flies gathering on a dead body, and we may need to resurrect the soil microbes in order to chase away the weeds?

  Sincerely,  Craig Dremann (650) 325-7333





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