The Formation of Good Arable Soil

Good arable soil is fertile, holds water like a sponge, and yet is well aerated. It is stable in itself and yet loose. Stone dust plays an important role in this.

How is good arable soil formed and how can it be restored?

Fertile soil is formed from decomposed rock in various stages and decomposed biomass. Useful microorganisms then settle there and provide structure and necessary transformation processes; symbioses with fungi and bacteria develop.

To approach humus building holistically, it helps to understand the entire process. Every soil starts with the rock, which is mechanically crushed by water, earthquakes, and other natural forces.  Water carries the rock grit to the plains where it is transformed into humus with organic remains such as dead plant (parts) and excreta and remains of animals.

Adding only organic matter to one's field can result in deficiency. Therefore, for successful stone fertilization, it is crucial to understand which volcanic rocks one's own field consists of, which mineral elements are naturally present and which are not. Supplemental fertilization with a different type of rock can be useful here. Iron consumers such as leafy vegetables need to be fertilized differently depending on the soil, and again quite differently than oats, for which the trace element manganese is particularly essential instead of iron. In animal husbandry too, a copper or cobalt deficiency can be manifested by infertility and deficiency diseases such as Hinsch's disease – cattle on granite-bearing soils are affected, for example.

Stone dust – nutrient reservoir and carbon sink

The fertility of stone dust can be understood in a particularly catchy way by looking at the Nile mud – until the construction of the Aswan Dam, the Nile regularly overflowed its banks during the rainy season, leaving enormous quantities of the weathered stone of the Abyssinian mountains on the surrounding farmland. This phenomenon is also known from other areas; generally, areas at the foot of mountains are particularly fertile.

Systematic stone dust fertilization was discovered in Switzerland over 90 years ago and the successes still speak for itself today. 

Humus supports the uptake of trace elements by plants, but these must be present in the first instance. The weathering of rocks in the soil releases the nutrients bound in them and in the process binds CO2 firmly in the soil: a win-win situation.

What does "rock dust fertilization" look like in practical terms?

Rock dust is not a fertilizer, but a soil additive. It therefore does not fall under the fertilizer ordinance.

If you produce your own compost, stone dust can be added to stable litter or to the compost, approx. 5–7 kg per 100 kg of compost or manure. In the stables it has other innumerable advantages for animal health and improves the stable air. Otherwise, it can be added directly to the plants – in fruit, grain and corn cultivation, about 10 kg per 100 sq. m. of area has proven effective (this corresponds to about one ton per hectare per year).

The importance of trace elements for human health

In addition to carbohydrates, fats and proteins, humans depend on a daily supply of vitamins, minerals and trace elements. Not only do plants grow optimally when the necessary minerals and trace elements are abundant in the soil but human health cannot do without any of the components in the long term either.

“Trace elements” are so named because they are found in extremely low concentrations – in healthy humans as well as in healthy soil. The targeted "fertilization" is therefore particularly difficult – very quickly it can be oversaturated. This can be dangerous for the health of plants, humans and animals. A good compost is able to compensate for this because the microbes contained in it absorb an excess of trace elements, fix them, precipitate them or bind them to humus acids.

However, without danger, the soil can be improved by primary rock dust because the trace elements are still bound in it and must be released by the plants themselves; the roots release acids (citric, hydrochloric, nitric and fluoric acids) and break the solid bonds – little by little. Grus (crushed stone) of about 1-2 millimeters in size and flours of about 0.1 millimeters in diameter weather at different rates. For a direct effect, therefore, rock dust is preferable; a more long-term effect is achieved with Grus.

Do you already have experience with rock dust? What other alternatives do you know?

[This article is inspired and summarized from E. Hennig's book "Secrets of Fertile Soils"]