crusher dust (forum)

srt starts with ...
Just bought 500Kg of crusher dust for $20. Seems it has a good rep. amongst olive growers as mineral additive . A little worried by its high pH of 9 but I am thinking of mixing in elemental sulphur to counter the dust's alkalinity. Any thoughts?

Time: 3rd February 2015 9:16am

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jakfruit etiquette says...
Crushed what ? Basalt ? Limestone ?
Superfine lime etc is like talc powder, used for fast pH adjustment, your crusher dust wouldnt be that fine so should have slower pH response, also depemds on how thick you apply. Whats your soil pH now ?

Time: 3rd February 2015 9:44am

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sternus1 says...
Depends wha you're using it for. And how define 'dust'. If it is truly powdered then you've hit a home run. Vegetables go crazy for it especially coniferous greens. No good for citrus really as it is too alkaline and takes many many years to break down.

If it is little chips, then it's not good for anything. It will raise your soil temperature and cause root burning and cloying, especially if you're on a heavy soil.

I have used crusher dust on bananas, blueberries, cacti and guavas. The guavas hated it, bananas liked it, cacti loved it, blueberries seemed to not even register its presence but it certainly didn't affect their health despite the fact t they are acid loving. I got a little bit of benefit bug this was probably owing to increased aeration caused by remixing.

Time: 3rd February 2015 9:44am

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srt says...
Crusher dust ,I understand, is a by -product of blue metal processed for road building. The base rock, I'm told, is basalt. as such it is a lot cheaper to buy than over priced "volcanic rock dust" sold at your bespoke garden shop.

Time: 3rd February 2015 4:14pm

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sternus1 says...
Don't think of it that way though. You're right-- it is road base, or bluestone. It's not in the same league as volcanic rock because it isn't porous like volcanic rock, which is why the volcanic stuff is more expensive-- that and it's harder to get.

Again, if it is in powdered form you can use it it in all kinds of ways. It's a cheap substitute for rock flour.but if it is little chips, you might as well use it as fill in a box slab for a water tank. Take a handful of it, wet it, let it dry and watch what happens. It will turn into a crust because it wants to bond with itself over other material around it. When you furrow it in do so slowly for this reason, otherwise you will end up with clods of bluestone which will be the same as rocks in your soil.

At 20 bux you can't lose though really.

Time: 3rd February 2015 7:09pm

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MIke T1 says...
Crusher dust can be various rock types including basalt and blue metal is basalt but dense non vesicular basalt.Basalt is the the most fertile volcanic parent rock being fine grained because the lava cooled fast unlike granite that cooled slowly.Vesicular basalt breaks down faster holds water better so is less inert than the denser blue metal road base but the same rock type.

Time: 3rd February 2015 9:48pm

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srt says...
Yes, I have used crusher dust to make a pad for rainwater tanks. Funnily passion-fruit , cherimoya seedlings and Rubus have self sown at the base of the tank. So it seems its alkalinity is not too much of a problem. As for the speed of mineral release I cannot see that being critical. After all an apple will be around for decades; maybe more important for veg. growers.PS Sternus Basalt IS volcanic rock. So what is "rock dust's parent rock?

Time: 4th February 2015 10:52am

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sternus1 says...
Ok well scoria for example is a type of volcanic rock that is porous and is sold commercially and it is much better than bluestone because of this.. It is also high ph. This has implications for levels of boron and other te's.Rock dust might be made from scoria, limestone or granite. It sold as rock flour for hefty premiums.

Again, I didn't notice anything negative relating to to ph when I used it in a mix for potted blueberries.

I believe if you go back and search the boards you yourself said that this was a bad idea because of its alkalinity, to which I replied that it takes a long time to break down. And now here we are.

Time: 4th February 2015 1:18pm

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MIke T1 says...
Scoria and quinkan is vesicular basalt.Rock flour or dust such as min + is pulverized vesicular basalt and it allows some of the elements to be released very slowly and the rock itself releases nutrients really slowly.

Time: 4th February 2015 8:15pm

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jakfruit etiquette says...
The particle size of the crushed basalt rock for remineralisation is very fine, like that produced by glacier activity, ie ice flows grinding down rocks. The theory is that the mineral levels in soils are depleted over the history of the earth, but renewed during the ice ages (and volcanic activity in those areas).
Modern Agriculture has sped up the mineral depletion in soils.
Mechanically grinding and broadcasting the rock flour imitates the process of mineral replacement.

Time: 4th February 2015 8:48pm

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MIke T1 says...
This material might be a little alkali but has only limited ability to raise soil pH.

Time: 4th February 2015 9:05pm

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For eddy says...
Crusher dust is vastly cheaper than your garden shop volcanics .....so ; if it is slower to act then why not use much more of the stuff. You are still way ahead. There are several trials on line for olive cultivation but ,then again, olives are not sensitive to alkaline soils.

Time: 5th February 2015 1:06am

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jakfruit etiquette says...
Well you will get the most bang for your buck( literally get your rocks off? )with the very fine grade particles of rockdust. You could screen a sample of your bulk load and work out the % of fines in it. Then calculate the price per kg of the fines from your 500 kg@$20.
ie count anything graded above fines as essentially inactive
Assuming other products have a similar mineral analysis, you can work out the equivalent value. As you say, even at 10% to 20% fines in your 500kg it is still cheap.

Time: 5th February 2015 8:32pm

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srt says...
Quite so Jakfruit. However, one ought not assume anything larger than powder is inactive . There can be ion exchange over large surfaces and one needs to remember that basalt erodes quickly unlike ,say, granite. Witness the basalt statues in Bali that erode from day 1.

Time: 6th February 2015 9:06am

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MIke T1 says...
It needs to be really fine to be active as nutrients are tightly bound so a big surface area is needed.

Time: 6th February 2015 8:37pm

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