Wikipedia:Reference desk/Archives/Miscellaneous/2024 March 8

= March 8 =

Rock dust as soil amendment
So, I've been getting my hands very dirty, trying to grow Hawaiian gardenias in containers. At the end of the day, I hope to put some of this experience to work writing articles about Hawaiian gardenias, but that's still some time in the future. One of the reasons I'm doing it is because gardenias can be very difficult due to their requirements, so it's a bit of a fun challenge for me. One thing that has me curious is the use of rock dust (mineral powder) as a soil amendment. The literature is bit odd on this subject due to the history of its use. Some people say it is just a trend and is not needed, while other gardeners swear by it. It's the only thing I haven't used yet, so I'm curious what the state of the literature says about it for container gardening. Is it helpful and will it make much of a difference for the plant, or can I get the same results using something else? Viriditas (talk) 21:09, 8 March 2024 (UTC)


 * A search for "controlled+experiment"+"rock+dust" yields mixed results – mainly involving the growing of tomatoes. Some report a positive effect, others no effect. (As far as I checked the search results in more detail, none reported a negative effect.) Most were not up to scientific standards, whether in the setup itself, or in the reporting of the setup (which should be detailed enough to allow replicating the experiment), or in the reporting of the results (which should be detailed enough to make statistical hypothesis testing possible). One study, which reported a significant (but small) positive effect of Azomite® on tomato crop, may pass muster. One issue is that there are many potentially confounding factors. What works for Solanales may not work for Gentianales. What works in soils with low pH may not have an effect in soils with high pH. The mineral composition of the rock dust and its granularity can be expected to make a difference. And so on. --Lambiam 12:04, 9 March 2024 (UTC)
 * Thank you. It looks like some studies show an increase in nutrient uptake leading to faster growth and yield in corn treated with basalt rock dust. Viriditas (talk) 22:18, 9 March 2024 (UTC)
 * At a very general level, basalt is what comes out of volcanoes, and historically people have tended to live by/on volcanoes because the soil is (reportedly) very fertile, so that would make some sense. {The poster formerly known as 87.81.230.195} 176.24.44.161 (talk) 03:35, 10 March 2024 (UTC)
 * The farmers at es:La Geria found that the lapilli that covered their fields reduced evapotranspiration. --Error (talk) 12:53, 11 March 2024 (UTC)
 * Declaration from the Brazilian Agricultural Research Corporation (Embrapa) on the use of rock dust:
 * Therefore, Embrapa's official position on this topic is that, currently, there is not enough scientific information to recommend silicate agrominerals as a source of nutrients, especially potassium, or soil conditioners for agriculture.
 * They announce a project to assess its agronomic potential in various production systems, including biologically based ones, and, if there is scientific proof of their usefulness in agriculture, recommendations for these materials (dose, source, time and form of application) in different production systems, based on their characteristics and soil indicators. The project is now running and slated to end in April 2026. --Lambiam 06:04, 10 March 2024 (UTC)
 * There is a huge variety of rock and therefore of "rock dust", but the rock dust known as sand is of course widely used to improve drainage, which is generally regarded as a good thing. Shantavira|feed me 17:41, 10 March 2024 (UTC)
 * Correct. The growers I've been following recommend basalt and glacial rock to increase nutrient uptake, growth, yields, and flowering, but I'm not sure it would make much of a difference for hobbyist container growing. Viriditas (talk) 20:11, 10 March 2024 (UTC)
 * Is "glacial rock" just a marketing buzzword? Glacial erratics are rocks and boulders that have been picked up by glaciers and deposited some distance from their origin, but it's not clear to me how that makes them helpful to plant growth more than, say, rocks that have been moved around by human labour. Matt Deres (talk) 17:25, 11 March 2024 (UTC)
 * It's discussed in the article on rock flour. Viriditas (talk) 20:43, 11 March 2024 (UTC)