In working over soil on my plot, preparing areas for planting, I have been doing a lot of raking to remove larger stones. I've been doing this largely because they can be a bugger when it comes to digging planting holes later.
So I find myself wondering about stones in the soil. I'm thinking about small stones; ones that don't interfere much with using a trowel.
If these smaller stones serve a useful purpose, I should try not to remove them when raking (or sieving). And if they are lacking, maybe I should import some.
So - Do small stones serve a useful purpose in soil?
Possibilities:
1. Modulation of available moisture.
Stones absorb water, capillary action taking it into microscopic crevices in the crystalline structure. I suspect that water is relatively slow to move out again, so I can imagine it acting along the same lines as the gel/pellets you can buy to act as reservoirs of water, especially in the soil of pot plants.
Also, the slow absorption could help to take-up temporary excesses of water.
2. Nutrients.
As water moves in and out of some stones, some nutrients may be dissolved and transported, becoming available to plant roots. By the same token, of course, adverse chemicals could also be transported (eg. calcium could be leached from chalk stones, which would not be appreciated by calciphobes.)
3. Root anchoring and depth.
A plant's roots are likely to penetrate the soil at a certain rate per volume of penetratable soil (subject to various conditions). If the bulk volume of soil is partly composed of stones, the remaining (penetratable) soil will be less, so the rate of root penetration will be greater relative to the bulk volume. (I know: that could be clearer: sorry.) My point is: If a plant's roots grow at a certain rate, in stony soil they will be able to anchor themselves in a greater bulk volume of soil than if the soil was stoneless. Better anchoring equals better resilience against the wind. That could also result in the roots penetrating deeper, and hence possibly gaining access to moister soil at depth.
4. Bulk.
By removing stones, one would decrease the overall volume of the soil. That could require extra soil to be imported. It is also possible that disposal of the removed stones could be a minor problem.
5. Appearance.
If the stones are a contrasting colour to the soil, the ones visible on the surface could be visually distracting. For example, white stones can look wrong in/on a dark soil, especially if the plant(s) have white flowers against dark- or no foliage.
6. Other?
I am ignoring particular issues such as stony soil giving problems for the quality of some root vegetables.
And I am considering just mediterranean gardening (the issues in cold temperate climates could be different).
Well, those are my thoughts, so far.
I'd be interested in your comments, dear reader, especially if you know of any scientific papers on the subject or if you have done experiments yourselves, or have relevant first-hand experience.
