Rock dust hurting are soil?

So i was trying to find some research on rock dust just because it didn't really make since to me. I mean ya it sounds good rock= minerals, plants have minerals= i should add rock dust...But to me the thought was its a rock none the less my plant cant eat a rock even that fine dust will take a long time to brake down enough for my plant,my soil should have minerals in it already shouldn't it? and if it does help my plant why cant i just add some hole river rock to my soil? So anyway i found this article and video an thought some of you might be interested in their findings. website https://www.gardenmyths.com/rock-dust-remineralize-earth/

video
Rock Dust – Can It Remineralize the Earth?
By Robert Pavlis on March 12, 2018

Rock dust is a very popular soil additive especially with organic and permaculture groups. It is full of nutrients and adding it to soil will replenish all of the nutrients that agriculture has taken out of our soil. This process of adding nutrients back to soil is known as mineralization.

This seems to make a lot of sense. We remove food from the land, and the food contains lots of minerals. At some point we need to put them back into the soil or else we will have soil that won’t grow anything. This seems logical but is it really true? Is our soil losing fertility? If it is deficient, can rock dust be used to solve the problem? How effective is rock dust and which type of rock works the best? Time to crush some myths about rock dust.


Azomite – a common brand of rock dust


What is Rock Dust?
The simple definition is that rock dust, also known as rock powder and rock flour, is pulverized rock. It can be man-made or occur naturally. Cutting granite for commercial use produces granite dust. Glaciers naturally produce glacial rock dust. Rock dust is also found near ancient volcanoes and consists of basalt rock.

To be effective the rock needs to be ground into a very fine powder. That way it is more easily used by microorganisms and decomposed by environmental elements.

Two common forms of rock, namely limestone and phosphate rock have been used for a long time to amend soil. Although these products are correctly called rock dust, they are usually not included when gardeners talk about rock dust, and I will exclude them from this post.

Is Rock Dust a Fertilizer?
Some commercial products call themselves a fertilizer and I even found one that was labeled like a fertilizer showing an NPK of 0-0-1, but by most legal definitions rock dust does not contain enough NPK to qualify as a fertilizer.

Claims Made for Rock Dust
Rock dust is claimed to add all kinds of minerals back to soil. These are the nutrients that plants need to grow. Because of this, rock dust products make all kinds of claims for growing bigger plants, producing higher yields, increasing disease resistance, etc. These are all valid claims if the soil is deficient of one or more nutrients and rock dust adds the missing nutrient.

There are two clear questions we must answer to validate these claims and I’ll do that in the rest of this post.

Does rock dust add plant available nutrients to soil?

Is soil deficient of nutrients?

If the answer to either question is no, rock dust will not help plants grow.

Before answering these questions, let’s look at some other claims made for rock dust.

Helps restore the correct mineral balance in soil
To be true, this would mean that soil has some kind of “correct balance” to begin with and that this balance is important for plant growth.

It turns out that there are many different kinds of soil, and they vary widely in their mineral composition. There are plants that are adapted to and grow on just about any soil. There is no such thing as a “correct mineral balance”.

When the correct balance is achieved organic matter is turned into humus
I have news for these companies, microbes turn organic matter into humus in all kinds of situations. In leaf mold it is done without any soil. This is just nonsense from a marketing person reaching for straws.

Plants can complete their life cycle without the full range of minerals but will not produce at their full potential
If plants don’t have the nutrients they need, they will not complete their life cycle – instead they die.

Analysis reports show Lanthanum (La), Cerium (Ce) and Praseodymium (Pr) at 644 ppm
These are rare earth elements, which makes it sound as if you would want them in your soil – who does not want rare stuff? I have heard of the first two, but not praseodymium – I must have been away the day we did experiments with it!

The claims go on to say, “These elements act as cofactors for the methanol dehydrogenase of the bacterium Methylacidiphilum fumariolicum.” So what is this important bacterium?

Methylacidiphilum fumariolicum is an autotrophic bacteria, first described in 2007 growing on volcanic pools near Naples, Italy. It grows in mud at temperatures between 50 °C – 60°C (about 130 °F) and an acidic pH of 2–5.

I guess if you are gardening in hot acidic mud, you might need these rare earth elements to keep your autotrophic bacteria alive. For the rest of us, we don’t need these elements in our soil!

Basalt, an igneous rock wasn’t processed or transformed by the environment, so the plant nutrients in it, are just as they were when they came out of the center of the Earth
This marketing person seems to be unaware of the fact that the minerals in rocks can’t be used by plants until the environment, or life forms convert them into usable nutrients. “Transformed by the environment” is a good thing.

The other desirable quality of the best rock dust powders is that they are paramagnetic
That may be true, but there seems to be no published research to show that paramagnetic rock has any affect on plant growth. However, many pseudoscience groups do make such claims.

Mineral Content of Rock Dust
Rock dust does contain a lot of minerals. I have seen claims ranging from 60 up to 90 different minerals. Azomite is a common product and their analysis list of 74 minerals can be seen here.

I don’t dispute the claims, but there is no evidence that plants need all of these minerals. They use about 20 minerals – that’s it. The other 40 to 70 are not needed by plants.

How Much Should You Use?
I find that this question can tell you a lot about a product. If rock dust is good for gardens, how much should you use? What happens if you use too much?

One site had this recommendation;

3 tons/acre = 14 lb/100 sq. ft. = 1.25 lb/sq. yd.

or

7.5 tons/ha = 750 kg/1000 sq.m = 75 kg/100 sq.m = 750 grams/1 sq.m

But a rate even 8x higher can be used, although it would have to be incorporated into the soil.

You can add anywhere from 3 tons/acre to 24 tons/acre. If 3 was the right number, would 24 not be way too much? Would 24 not burn plants due to the high nutrient load? Only if the product actually added nutrients to soil.

Rate of Decomposition of Rock Dust

rock dust mine

Earlier in this post, I posed the question, does rock dust add nutrients to soil. There is no doubt that adding rock dust adds the minerals, but I can also do that by laying a big bolder on top of the garden. The bolder will not help plants grow but it does add minerals to the garden. Unless the minerals in the rock decompose to release the nutrients in a form plants can use, there is little point in adding the rock dust.

For this reason I think that one of the most important questions we need to ask is, how quickly does rock dust decompose?

Some of my early reading on the matter indicated time frames of a hundred years. I have searched on many web sites selling rock dust and none have any claims or data to show decomposition happens even after 100 years or more. No one in the industry wants to put a number on this important property.

My recent visit to the Guelph Organic Conference allowed me to discuss rock dust with two suppliers. Neither one has been able to supply any details about decomposition. One never claimed to have such data, and the other only has it available in French only – but they did not provide it.

Google Scholar produced no research paper that looked at the rate of decomposition of rock dust.

The best information I have is a casual comment that it is about 100 years. At that rate the product is essentially useless.

If you find some numbers on this please post them in the comments, or even better post them on our Facebook Group, called Garden Fundamentals.

Are Soils Nutrient Deficient?
This is also an important question to ask. Do we have a problem that needs to be fixed?

I had a closer look at this question in a previous post called Is Soil Fertility Decreasing? My conclusion was that our soils are not losing fertility. They are not nutrient deficient. Therefore, rock dust, assuming it actually works, is a product that tries to solve a problem that doesn’t exist.

What Does Research Say?
Some papers report some improvements in plant growth with some soils but many show no change. There is limited field work done – it is almost all lab work. I did not find a single paper that measured the chemical characteristics of soil before and after adding rock dust to the field – maybe you can find one for me.

There is some evidence that rock dust may provide an important source of potassium in regions like Africa that tend to have soils which leach nutrients quickly and where fertilizer costs are very high.

The science does not support the use of rock dust for most agricultural areas and even the suppliers of rock dust suggest it has no value in alkaline soil.

What about some citizen science results? This trial is interesting.

rollangrow said:

Click to expand...

I use Basalt for iron, and that's about it..

I only use 1/2 cup per cu ft as that's all I need. Saw no difference in using 1/2 cup vs 4 cups per cuft of soil.

Kelp gives me everything I need trace mineral-wise and is available a lot sooner.

Each year i add volcanic rock dust to my 5 gallon soil container I add third off a cup .
Each pot

The principle not being looked at is symbiosis.. much availability depends on this.. plants do not work alone.. they employ fungi, bacteria, enzymes, and a long list of other species to help them attain the things they need to get done.. in a natural state anyway. A funny example is how many wealthy ppl rushed to invest in the big Truffle farm trend, but failed to succeed as they failed to understand that myco fungi was the symbiotic factor required to help hazelnut trees produce these expensive special mushroom type things.

Personally, I've seen fungals immediately flourish in a rock dust (glacial sand) top dress .. literally within a couple days of applying.. bam, they came up to start breaking them down. That plant also grew the fastest that round.. like 2 to 3 inch a day everyday..

The most stupidly productive veggie garden Ive ever seen, dude was big on his GRD in his AACT's.. world record holder knew how to produce monster fruits.. and did so from wee little northern Alaska.. GRD being his major weapon

I also live in the Rocky Mountains, and see trees growing in nothing but sands and rock dusts.. minus the thin top layer of leaf mould, which is fungal dom in nature, as white rot fungus is a necessary prerequisite for any leaf mould or rotting wood.. interesting hey!

and the 2nd vid in post #3, that farmer is a actually big advocate for GRD, he goes on to explain that microbiology is key factor.

Lastly, I took a plant once that was almost dying, this Gogi OG from Gnome was yellowing top to bottom, about to bite the dust a couple weeks into flower.. I took some GRD, top-dressed the plant, and pollinated it with some SBK/Grape Lime Ricky type pollen, and let it go outside.. I was in the middle of a move, and before leaving the province I came back for a tester... it got SO green, SO healthy, and produced the TASTIEST HEALTHIEST herb of the summer, AND viable seeds on top of that too!! I was like, dang.. the GRD was the only thing I added outside the original old soil mix, and the end taste was off the walls, major lingering action! Of course much of this was genetic, but that plant was so gonna DIE, next thing you know it brought me a new strain and a major taste / turnoaround experience to boot. Interesting to note, this plant was an experiment in NOT using bene's, no myco fungi or FRASS, and a smaller pot, which will kill bacteria faster, all of which likely led to its low level of bio availability in the first place.

Ps. Azomite is an inferior example of GRD imo.. it was named such after they found everything in it from A to Z, literally, including heavy metals and a whole host of shit plants don't need.. there are much cleaner profiles out there!!