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No need for mineral supplementation?  RSS feed

 
Ben Bishop
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Hello!

I've heard some interesting research recently from a friend who works with Elaine Ingham. The theory is basically this: Nearly all of the minerals needed for proper plant growth with the exception of nitrogen and carbon can be found in an inorganic form in most soil types. To access these minerals, plants secrete specific types of root sugars at specific times to attract specific microbes that "mine" for whatever mineral that plant needs at that particular moment. In other words, by ensuring adequate compost and compost tea applications and fostering high microbial life, you will mitigate the need to supplement any type of mineral into the soil. What do you all think of this? I'm having trouble confirming the idea that magnesium, calcium, phosphorus, potassium, etc would be A.) present in a good balance in all soil types and B.) be abundant enough to support heavy-feeding plants. However, this theory makes sense to me and I want to believe it!
 
John Elliott
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There's a good amount of logic in this thinking. Animals contain all these minerals, and when they are done scurrying over the landscape, they fall down and die and the lucky plants nearby can benefit when they decompose. In addition, there are soil fungi under the ground that transport minerals along their mycelial networks, moving minerals from where they are to where they are needed.

In his book Collapse, Jared Diamond talks about another source of minerals, in this case the trace elements: volcanoes. Volcanic eruptions will throw ash up into the stratosphere, and as it settles out, it provides a new source of minerals like cobalt (vitamin b12), molybdenum, selenium, and other elements needed by living organisms, but in much smaller quantities. He notes that the explanation for Australia's lack of vegetation compared to the other continents is that it is not downwind of many active volcanoes, thus the soil is inherently poor in trace elements. When the elements just aren't there to begin with, then yes, mineral supplementation is needed.
 
Ben Bishop
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Good points John. Your last comment about needing to supplement when the mineral is "just not there". Are there instances where something like calcium, potassium, magnesium, etc, the macrominerals, aren't present in the parent rock material and clay/silt/sand? Could there adequate amounts of micronutrients locked up in the rock but not present in soil that only microbes could get at?
 
John Polk
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As nice as that theory sounds, I believe that there are flaws (or at least limitations) to it.

Yes, most soils have trace amounts of most of the minerals. In very sandy soils, these elements may have leached so deep that no root will find them. In other soils, previous vegetation may have consumed these elements. If large quantities of produce have been exported off of the farm, these elements went with them, leaving the soil depleted of vital elements, unless they have been replaced.

It is true that compost and compost teas will return some of these nutrients, but if the soil the compost was grown in was already low in these minerals, the compost will also be low in the minerals. You would be returning very tiny amounts. Even if the compost/tea is deficient in these minerals, it still has value in helping the soil food web do their job of maintaining a healthy soil, but not as much value as it would have if the soil had abundant supplies of these minerals.

Many of these minerals were added to the soils either when the glaciers ground up the rocks, or a volcano erupted. If each crop is using trace amounts over centuries, eventually, these minerals will become depleted unless replaced.
 
John Elliott
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Ben Bishop wrote: Are there instances where something like calcium, potassium, magnesium, etc, the macrominerals, aren't present in the parent rock material and clay/silt/sand? Could there adequate amounts of micronutrients locked up in the rock but not present in soil that only microbes could get at?


I imagine that on sand dunes, where you have miles and miles of nothing but little quartz granules, the need for mineral supplementation will be very great. Take for example the Kelso Dunes in the Mojave desert of California. Since they were formed by airborne sand piling up over the eons, there is very little in the way of minerals to be found.



But I suppose you guess that looking at the vegetation. Of course, when you get out of the dune area to a place with real soil that was laid down by sand/silt/clay eroding down from mountains, then the mineral balance is closer to "normal".

As to the availability of micronutrients, a lot of them are locked away, for example as insoluble sulfides. Consider pyrite, iron(II) sulfide. You can find it in a lot of soils, and it is pretty common in sand in the California desert, but it is not a source of iron for plant roots. That particular sulfide is very, very insoluble, and the only way to free up that iron is to attack it with acid. This is where the soil microbes come in. Their digestive enzymes may be able to attack and dissolve pyrite, and in so doing, pull the iron into a biological cycle.
 
Peter Ellis
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Ben Bishop wrote:Hello!

I've heard some interesting research recently from a friend who works with Elaine Ingham. The theory is basically this: Nearly all of the minerals needed for proper plant growth with the exception of nitrogen and carbon can be found in an inorganic form in most soil types. To access these minerals, plants secrete specific types of root sugars at specific times to attract specific microbes that "mine" for whatever mineral that plant needs at that particular moment. In other words, by ensuring adequate compost and compost tea applications and fostering high microbial life, you will mitigate the need to supplement any type of mineral into the soil. What do you all think of this? I'm having trouble confirming the idea that magnesium, calcium, phosphorus, potassium, etc would be A.) present in a good balance in all soil types and B.) be abundant enough to support heavy-feeding plants. However, this theory makes sense to me and I want to believe it!


Here are my thoughts: "most soil types" is a very long way from "all soil types". A definition of "good balance" is called for. Abundant enough to support heavy feeding plants does not necessarily go along with "good balance" - inherent in the phrase "heavy feeding" is the idea that the plant is demanding in ways that go beyond an "average" sort of balance.

I expect that when you look at the native plant life in an area - and we can go ahead and include non-native invasives for this exercise, because this is all about being successful - what you see growing well tells you a great deal about the soil. Lush growth, "heavy feeding" plants doing well - tells you that soil has lots of everything a plant needs. Looks like that sand dune, with some sparse grasses and only the hardy pioneers that can survive on practically nothing, well, they're surviving there on practically nothing

The plants that survive in a given place are doing exactly what is theorized - making the deals they need with the microbial life to get the minerals they need from the soil. But that does not mean the minerals are all present and well balanced, it means the plants growing there are adapted to what is available.

And it may be that there are more soil types, more soil conditions -however one chooses to phrase it - where there are sufficient minerals available for most plants, than there are soil types that are damagingly deficient in mineral availability.

I am not sure what that information means. Possibly that before we go adding minerals we might want to make sure we have adequate microbial populations and systems in place, as without them the plants may not be able to access the added minerals, and with them it may not be necessary to add the minerals after all.

I do not think that this information suggests there is no need for mineral supplementation, but rather that we may be turning to mineral supplementation prematurely and inappropriately in some cases.
 
Bryan Jasons
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Where is the data that shows the insoluble and soluble minerals in soils? If a soil had very low levels of minerals available in soluble forms but the parent material had lots, then the idea is pretty much confirmed, right?
 
Michael Vormwald
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<deleted as my response was more targeted at a typical vegetable garden rather than 'permaculture'>
 
Bryan Jasons
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Ok, so as far as Phosphorus is concerned, what Elaine Ingham says seems to be true :

"The inorganic phosphate compounds in this fixed P pool are more crystalline in their structure and less soluble than those compounds considered to be in the active P pool. Some slow conversion between the fixed P pool and the active P pool does occur in soils."

"Soils may contain several hundred to several thousand pounds of phosphate per acre. However, much of the phosphate in soils is not available to growing plants. Phosphate in the soil solution P pool is immediately available but the amount is very small in comparison to the total P in soils."

http://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/

http://www.soils.wisc.edu/extension/area/2003/Bundy_stp.pdf
 
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