I have to agree with LL's comments on this. Organic gardeners are the ones
using rock powders in best ways. They should be given preference in the use
of these resources. Here in Trinidad dust from limestone crushers is used
to make concrete blocks when it could be used much more beneficially to
amend soils. There is a tremendous waste of these resources.
No system of "agriculture", even organic, is perfectly sustainable. One
cannot prevent soil erosion completely. If mulch and compost materials are
brought in from another site we are depleting that site. Mulch or compost
material grown on site will not remedy the mineral deficiencies of the soil
on the same site. Availabilty of phosphorus is very often a limiting factor
in tropical soils. The developed countries use much more than their fair
share of the world's resources.
Certainly we need to recycle phosphorus and other minerals as much as
possible, and prevent soil erosion. But I think it is harsh to criticize
the use of rock dusts by persons who are trying to practice sound
environmental practices in their crop production.