Sometime ago I was researching the topic “how to use different rock dusts (basalt rock dust, stone meal, granite rock dust, azomite rock dust, etc.) as fertilizers in agriculture.” Usually most of the research is clear – the more stuff you put in, the better the results are. 10 tons per acre/20 tons per hectare are often better than 1/10 of the dose, and even 20 tons per acre/40 per hectare are better. Although the price of rock dust is quiet cheap, the transport is not. My friend’s farm is about 15 hectares (37 acres); if he was about to fertilize his pastures with “just” 10 tons/ha, he would have to pay for 6 trucks of this material. That’s a significant cost!
Is there a way to get the benefits of the high rock dust usage without the high cost of transport?
There is! Most of the studies that used rock dust as a fertilizer were done:
On poor soils, like tropical soils, acidic soils, or sandy soils
On agriculture land that was fertilized with standard fertilizers
Usually the rock dust is the only source of nutrients for the plants. To be fair, it’s usually not the most economical way to provide our plants with micronutrients (copper, iron, boron, manganese, molibdenium, sulfur, zinc, nickel, cobalt) if our soil has a specific deficiency. It’s far cheaper to supply micronutrients in concentrated form.
Why don’t rock dusts work as well with lower application rate?
What’s not happening in the studies is scientists working with soil that has at least an adequate supply of macronutrients, micronutrients, and trace elements that are known to be needed for the plants. But what’s happening if the soil has them and we apply rock dust?
Then rock dust is a source of ultra trace elements that are probably lacking in your soil. Since nothing else is a limiting factor in your yields, rock dust, even in limited quantities, will give your plants (and later animals and humans eating them) a nice health boost. In those circumstances the dose can be quite low – e.g. 0.5–1 ton per acre or 1–2 tons per hectare.
Rock dust as soil amendment
Rock dust is also a soil amendment, not just a fertilizer, so on some soils it’s going to give you benefits regardless of its “nutritional value.” Some of rock dust’s soil amending properties include:
Providing “food” (minerals) for a wide variety of microbes. This helps to make minerals more available for plants
If you have any questions feel free to post a comment bellow!