Rock dust in 50 lb pails, how much do I need, Mr. Brown ?

jolj(7b/8a)March 26, 2012

The link you left on another thread, gave me a link in WV.

I have 48 X 44 plot.

Only 1280 feet is raised beds.

So for the size garden in sandy loam, never having rock dust before & no lime or micro nutrients, only compost.

How much dust do I need & how often should I apply it?

Everyone tell me what you would do.

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What material is it?

My direct experience with rock dusts at this point is short and inconclusive. I would go to remineralize the earth dot org and read.

    Bookmark   March 26, 2012 at 9:16PM
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Look at this video regarding rock dust and amounts

Here is a link that might be useful: Rock dust and amounts

    Bookmark   March 27, 2012 at 2:01AM
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Don Weaver from Remineralize the Earth recommends 1 pound for each sq ft as an initial dosage with annual replenishments of 1/4 lb per sq ft. The replenishment rate sounds excessive to me as the breakdown rate would seem to be a lot slower than that.

I built raised beds last year using only straw bales and compost. Because no soil was included I added Azomite and volcanic dust/sand I had collected next to a quarry at a cinder cone. I was very happy with my vegetables.

This year I am building four 4x8x2ft raised beds using concrete blocks. the left over straw/compost from the 40 bales I used last year and an additional load of 15 yards of local dairy compost will fill my beds. To this I will add the 6 buckets of volcanic dust/sand I have and probably 6 bags of Azomite.

The buckets of volcanic sand/dust I use come from outside a red cinder cone quarry in California. It is blown by the winds into small dunes. When I drive from Idaho to Southern California, I always stop and fill up 3-4 Home depot buckets. Figure the mixture will complement Azomite or Green Sand or whatever else I might find locally.

I know the purists will always say to do a soil test (apologies to kimmsr), but since we are starting out fresh without soil, I will add it now and adjust later.

Here is a link that might be useful: Another Don Weaver video

    Bookmark   March 27, 2012 at 2:56AM
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Do you need to add these things? Without that soil test how will you know? Will you be spending money on something you do not need, ie. throwing your money away?
Back in the 1960's the thought was that adding these rock dusts would bank (save) nutrients but recent research indicates that excess amounts of Phosphorus in soils causes problems with our water supply, ie. toxic algae blooms in our lakes. Some of this is from improperly handled animal manures but much is from our lawns and gardens and is why many states have banned the sale of fertilizers containing Phosphorus unless you have a soil test that shows a deficiency of that nutrient.

    Bookmark   March 27, 2012 at 6:34AM
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A soil test is not the only way to judge soil, and it may not be the best way. Soil is part of the system that produces plant food we want to eat, or feed to livestock. What really wants judging is the overall system, and if it lacks various things may need altering, not just soil. The brix test is on the opposite end from the soil test. If other factors are controlled or known about, then brix tells about soil fertility.

A big advantage to it is that it tells about what has already certainly happened rather than what might happen, as a soil test does. The strong acid soil test tells about minerals that might or might not be available to plants, the brix test tells what levels have in fact been taken up. So without that soil test how will you know that you need rock powders? If you have consistently low brix tests. Absent the refractometer well-calibrated tastebuds can make the same judgement. If produce does not taste remarkably better than average grocery produce then the brix is not high enough and if other factors are adequate (moisture, sun fall, crop spacing, weed control) then the fault is the fertility level, which is itself based on mineral levels and diversity.

Kimm, your statement above is confusing phosphate rock powder with the phosphate fertilizers. I do not believe there is any evidence that phosphate-bearing rock dust is soluble enough to pollute groundwater. All the rock dusts require some microbial activity to have much release.

    Bookmark   March 27, 2012 at 7:10AM
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I ask, because you know more then I do about the rock dust.
The pail has Basalt microfines in it.
I am going to do a soil test, first to compare to the one I will do in 12-24 months to see what I have in the soil.
I agree that it is not needed to put out the dust or compost.
Many people put to much into test & research, when they should be asking can I trust this person & their data.
I think I can trust you & your data.
You start with the fact that on rock dust you are short on experience, still you know truck loads more about RD then I do.
I wanted to make sure I did not put out too much.
1 pound per sq. ft. is more then I am willing to spend.But some is better than nothing.
I am building this garden for myself, then my children & hopefully my grand children.
Thank you all for you replies.

    Bookmark   March 27, 2012 at 4:04PM
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toxcrusadr(Zone 6a - MO)

Coach Grumpy: I got curious and looked up your red lava rock. It is a form of basalt, but I was not able to find much on what exactly is in it. One source said their product is almost entirely silica, and gave the following numbers for trace elements:

Nitrate Nitrogen.................................4.0 p.p.m.
Phosphorus........................................6.0 p.p.m.
Potassium.........................................59.0 p.p.m.
Zinc.........................................................6 p.p.m.
Iron..................................................10.0+ p.p.m.
Copper...............................................5.5+ p.p.m.
Magnesium.......................................2.0+ p.p.m.
Boron.................................................10.0 p.p.m.
Sulfate.................................................7.0 p.p.m.
Organic Material...........................................5%
PH.........................................................8.2 Units
Calcium..................................1.3 Meq/100 gm*
Manganese...........................0.6 Meq/100 gm*
Sodium...................................0.1 Meq/100 gm*
Cation Exchange Capacity..3.2 Meq/100 gm*
* Milli-Equivalent per 100 grams

There may not be much to it that's worthwhile other than porosity which could lighten soil.

    Bookmark   March 27, 2012 at 4:24PM
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wayne_5 zone 6a Central Indiana

jolj, I used some Azomite which is assayed. I used a pound per 60 sq. ft. This is less than some recommendations but somewhat closer to what Fedco recommended. I am a bit cautious and since the shipping or traveling a ways to get it is pricey, I gave it a dusting....about 700 lbs to the acre.

My main concern is not to get some potassium or one of the macro minerals, but the micro ones like Yttrium, cobalt, strontium, Scandium, and some others. A regular soil test will not tell about these minerals and they may not be necessary for healthy plants, but rather necessary for more optimum human health.

    Bookmark   March 27, 2012 at 5:26PM
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toxcrusadr(Zone 6a - MO)

What you need is a bowl of Quarry Cereal. "Tastes great becuase it's Mined!"

SNL, ca. 1990. :-]

    Bookmark   March 27, 2012 at 6:35PM
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I am building this garden for myself, then my children & hopefully my grand children.


    Bookmark   March 27, 2012 at 9:40PM
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I am right now being considered for a plot of nice dead flat, stone-free loam to do testing of various materials. Even comes with a stipend of $500 from the USDA to buy materials. Hopefully I will be able to test two native mined rock materials and one imported stone dust in bulk (a pick-up truck load of each), plus small amounts of humate and azomite. All these will be in comparison to the control which will be simply the existing loam as is. I can get a rough baseline on the existing conditions by brix-testing the existing cover crop in as many different strips as there will be experiments.

It is written as a 10-month experiment but hopefully they will extend it to another season so that the same test strips could be run again with different crops to see whether the materials give a better effect over more time.

    Bookmark   March 28, 2012 at 7:10AM
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I can get a rough baseline on the existing conditions by brix-testing...

I see you referencing brix a lot lately. It is indeed a handy tool but I'd just like to throw out a little reminder not to get too hung up on it, especially to the exclusion of soil testing and tissue analysis in regards to soil fertility.
A good many things other than soil fertility can affect what makes it into the above ground growth such as air temperature, humidity, soil temperature, soil moisture, disease issues, insects, nematodes, seasonal fluctuations, genetics, etc.
Anything that affects (positively or negatively)a plant's ability to take up water and nutrients will affect the make up of the plant. Looking at only one "axis" on the chart can be very misleading. This is particularly true with brix which looks at a whole host of stuff in the tissue and yields a single result and doesn't differentiate between analytes.

    Bookmark   March 28, 2012 at 8:43AM
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toxcrusadr(Zone 6a - MO)

I was thinking the same thing, garg. Here at the U. of Missouri they have a test field that has been continuously cropped for over a hundred years, with meticulous records kept. It takes a long time to control out the variations in weather and the others you listed. The campus has grown out around this field but it has been scrupulously protected from development. It is the oldest continuously operating test field west of the Mississippi (or perhaps in the country, I don't remember). Sorry to wander off topic a bit.

    Bookmark   March 28, 2012 at 10:23AM
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I wonder if local granite quarries will let people dig from the piles of "fines" washed or sieved from crusher run gravel to make cleaned aggragate for concrete? That would contain much rock dust.

York County, SC, has a dacite mine which is mafic or almost mafic in rock type I believe and thus probably even better as a mineral source.

    Bookmark   March 28, 2012 at 11:41AM
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Point taken that no one type of test is conclusive. However I have to go with what i've got, which is likely a situation where I will have to hustle and set up test rows with no time for soil tests, by the time I am allowed onto the plot. I have to take advantage of early season moisture so my first crops are peas and fava beans, by the time the plot is mowed and disced it will past time to sow.

Brix has the advantage that I can do it on the spot at no cost. So if I am merely trying to establish whether there is significant variation in fertility on the scale of one row to the next, and I brix let's say the rye cover that is on part of the area, all at the same time, which has been growing the same length of time with the same rainfall and temps, doesn't it seem like a significant brix difference would indicate a soil difference? I don't expect to find any significant difference at all but it's an available way to rule it out. Soil tests are an expensive way to find a difference on a scale of feet, and since brix is going to be my output test measure in any case then it kind of makes sense for it to be the baseline measure as well.

    Bookmark   March 28, 2012 at 1:21PM
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wayne_5 zone 6a Central Indiana

Pat, I commend you on your possible experiment. The rest of
us here are like armchair advisers as far as your plot goes.

Don't expect full improved results the first year as rock dusts do not fully break down and absorb the first year.

The Rothhamstad plots are a hundred and sixty years old and were used to test different treatments.

    Bookmark   March 28, 2012 at 1:40PM
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doesn't it seem like a significant brix difference would indicate a soil difference?


Or it can mean that you've got a localized infestation of nematodes left over in one spot from last year's crop or even weeds. (and only the root knot can be spotted without lab testing and sometimes, not even them) If you've got sting nematodes or one of the other plant pathogenic species, you may not know and they can all infest fields in patches.

Or it can be due to differences in drainage characteristics, which can vary depending on things like foot and vehicle traffic, even assuming that the soil type is perfectly uniform.

Or microclimates may affect plant development. Like if you've got a prevailing wind from the north and the north row takes the the brunt of cold breezes and sustains some cold damage while protecting the south row, resulting in decreased ability to photosynthesize and produce sugars.


I suppose it's better than nothing but if the primary purpose is to evaluate soil fertility, I would be very hesitant to draw any conclusions, even tentative ones, based on something that doesn't measure soil fertility.

As far as having time to test the soil, you just have to grab a little dirt on the same day that you're planting and send it in. That would give you a good a good base line. A couple more samples down the road and you just might have something. The cost can be an issue but a lot of labs can give you some numbers for pretty cheap. You would just want to make sure you're choosing the right methods for your soil. (I can help you determine the correct methods if you like)

    Bookmark   March 28, 2012 at 2:44PM
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The first reason for the rock dust is the same as your, to make food better which will make us better.
The second, is because the dust will break down slowly over time. My time, my children's time & my grandchildren's time.
It is true many thing can go wrong or right in a test plot.
I for one, am glad you are doing this test.
Any test plot will tell you something.
I have not the time, money or energy to do these test.
Thank you for taking the time to make the garden world better. When you are Published, let us know.

    Bookmark   March 28, 2012 at 7:03PM
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