[Kristen]

Watrching some YouTube videos this side-by-side trial of Biochar and Rockdust (and a control) seemed to find that Rockdust reduced yield (50% less for Tomatoes, 75% less for Peppers)

7PCNmoMbKqU
they are intending to extend the experiment a further two years, but I was struggling to think of any reason why rockdust could significantly reduce yield 

Any ideas?

[JayG]

Well found Kristen, even though you have probably condemned me to watching all the other linked videos about the trials rather than doing what I'm supposed to be doing!

Biochar seems to come out of it looking far better than Rock Dust, possibly because of its nutrient-retaining properties, although soil physics and chemistry is so complex I'm sure there is much more to it than just that, and it doesn't of course explain why Rock Dust actually does so much worse than the control in most (but not all) cases.

Can't help wondering whether keeping your soil healthy with plenty of rotted manure and compost incorporated isn't the best, cheapest and easiest way of ensuring that most crops will thrive though.   

[BabbyAnn]

According to wikipedia

Rock dust is not a fertilizer, for it lacks the qualifying levels of nitrogen, potassium, and phosphorus

so if you added the rock dust, you would have a dilution effect on these macro nutrients but increase the micro nutrients such as the various minerals associated with it.  Maybe also it would have less water retention as well?

As for Biochar it

is a high-carbon, fine-grained residue

For plants that require high potash and elevated pH,[29] biochar can be used as a soil amendment to improve yield

The tomato yield from the Biochar experiment seemed to support the high potash theory although interestingly not the peppers - maybe the location of the various beds may have contributed to differences in yields too?

Can't help wondering whether keeping your soil healthy with plenty of rotted manure and compost incorporated isn't the best, cheapest and easiest way of ensuring that most crops will thrive though.   

  I'll go along with that although I'm perhaps one to try something out at least once just to be sure I'm not missing out on something.  Maybe rock dust in the long term may provide minerals where it is lacking in some soils but needs to be supplemented with a rich NPK source as well.

[mumofstig]

The fantastic yields they had in the Scotland were always rock dust PLUS lots of added compost IIRC.

[Kristen]

you have probably condemned me to watching all the other linked videos about the trials rather than doing what I'm supposed to be doing!

Whatcha think I'm doing this morning then, eh?!!!

Can't help wondering whether keeping your soil healthy with plenty of rotted manure and compost incorporated isn't the best, cheapest and easiest way of ensuring that most crops will thrive though

Watch this next then perhaps?

Am I Using Too Much Compost and Mulch?
G5d98JHuk80
and then the sequel :

No Such Thing as Too Much Compost?
k3fUy8_1qxU
Dunno if you have read the musings of Dr Linda Chalker-Scott (PhD, Associate professor in the department of Horticulture and Landscape Architecture at Washington State University)? I own and have read her book "The Informed Gardener" which makes interesting reading but, for me, just leaves more questions in my mind that the answers she provides. I have that problem with all her online material too - I want to ask "But what about X" - I don't find enough breath of evidence in her publications to convince me, but only to say "In these rather narrow circumstances X happened". Be interested to know if other folk have that too.

Much of he musings is available here (for when you have finished wandering through the YouTubes linked above )

Amongst the myths debunked are:

Don't stake new trees
Don't use Bone Meal when planting e.g. young trees
Water droplets don't cause leaf burn
Don't put crocks / gravel etc. in the bottom of pots (that's been known for 100 years or more, still common practice, I'm still not convinced its always wrong!)
Pressure treated timber (and perhaps more importantly: sawdust from pressure treated timber used in horticultural products) can cause harmful chemicals to be absorbed by plants
Ditto: water retaining gel will leach harmful chemicals into food crops
Pine needles won't acidify soil when used as a mulch
... etc ...

http://puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/index.html

[JayG]

Crikey Kristen - I think that lot might have to wait until I'm forced to watch some crummy film over Christmas!   

[Kristen]

Crikey Kristen - I think that lot might have to wait until I'm forced to watch some crummy film over Christmas!   

Ask Santa for her book? 

[Aunt Sally]

Oh Kristen  -  back on topic

Rock Dust

[Kristen]

Sorry.  Linda Chalker-Scott does debunk Rock Dust as a myth ... but what surprised me was that it could significantly reduce yields.

I wonder if the experiment was too small and even though large differences perhaps not statistically significant?

The earlier comments about amount of compost present represent a significant difference from the test scenario.  I've only used Rock Dust in small quantities, as the cost of using them at recommended dose (for a first time application on a virgin site) would have been pretty expensive.

The thing I'm struggling with is that providing a top up dose of micro nutrients would be able to cause a dramatic reduction in yield ... and whether the test conditions are actually the cause.

[solway cropper]

The problem with most of the stuff posted on youtube is that it has very little scientific validity. You can prove or disprove anything by setting up the test to give the result you want.

JayG hit the nail on the head by saying that the best way to grow good crops is in a healthy soil with plenty of added organic matter. Forget additives and anything that offers a quick fix. If you think your soil is deficient get it tested and only add what is required and in the amounts required.

[cadalot]

The one Yard at a time, does use science and field tests to report and support it's findings, I have to say it is one of my favourite YouTube gardening channels. 

[Kristen]

The one Yard at a time, does use science and field tests to report and support it's findings, I have to say it is one of my favourite YouTube gardening channels.

I enjoyed it too. I found it a bit disconcerting that the taste-one-Tomato test got different results on a second pass - clearly individual tomatoes had different flavours (to be expected )  - but it did make me wonder if the tasting-test was "robust enough" to help reach a statistically-significant decision.  The conclusion he drew ("How many times was any method voted Top" and "bottom") did look conclusive though.

[sunshineband]

Now there is a nice lot to occupy me when futile films appear of the telly 

I have to say however, that I added rock dust to the beds that spent a few weeks under water last year, as I felt this might replace some of the micro nutrients possibly leached out. All the beds, not only the rock dusted ones (except the ones for carrots and parsnips of course) also had as much compost and/or manure as I could lay my hands on as well, but those that had been rock dusted did give decent crops and not a lesser yield as far as I could see. I did not weight them to give an absolute result, but the tomatoes were certainly a heavier yield by far (Marmande and Harbinger) than those grown in non rock-dusted beds, as were beetroot (Boltardy and Chiogga)

It kept me happy anyway 

[AnnieB]

Thing is that on a small sample and short time and if you have an opinion one way you can prove almost anything.

The old saying: There are Lies, Damn Lies and Statistics.

They grow most tomato's, peppers etc in the UK these days hydroponically.
No rock dust, no soil, also the best yields come from glass houses that have CO2 at elevated levels. Tomato's apparently evolved when CO2 was higher and this preference is still there.