Rockdust

Rockdust, also known as rock powders, rock minerals, soil remineralization and mineral fines, is a non-synthetic organic fertilizer usually consisting of crushed limestone but which may also be crushed basalt (a volcanic rock) containing minerals and trace elements, used in organic farming.

Background

Rockdust is added to soil to improve fertility and has been tested since 1993 at the Sustainable Ecological Earth Regeneration Centre (SEER Centre) in Straloch, near Pitlochry, in Perth and Kinross, Scotland. Further testing has been undertaken by James Cook University, Townsville, Far North Queensland.

Research

SEER's research claims that the benefits of adding Rockdust to soil include increased moisture-holding properties in the soil, improved cation exchange capacity and better soil structure and drainage. Rockdust also provides calcium, iron, magnesium, phosphorus and potassium, plus trace elements and micronutrients. By replacing these leached minerals it is claimed that soil health is increased and that this produces healthier plants.

Typical composition table of rockdust

Element	Unit
calcium	%w/w	6.44
iron	%w/w	10.5
magnesium	%w/w	6.54
sulphur	%w/w	0.21
potassium	%w/w	1.25
phosphorus	Mg/kg	3030
cobalt	Mg/kg	35
copper	Mg/kg	43
manganese	Mg/kg	790
Molybdenum	Mg/kg	<5
zinc	Mg/kg	92
silicon	%w/w	21.6

Available Silicon
Silicon is thought to be the major element effecting the strength of cell wall development. However it is the amount of available silica that has a dramatic effect on the plant strength and subsequent health. To highlight this, plants that are grown in very sandy soils, (being high in non available silica), often require a silica based fertiliser to provide available silicon.

Silicon comes in silicon multi-oxide molecules (eg SiO2, SiO4, SiO6, SiO8 etc). Each molecule shape is thought to pack in different ways to allow different levels of availability.

Phosphate fixation
Often phosphorus is locked in soils due to many years of application of traditional fertilisers. The use of micronutrient rich fertiliser enables plants to access locked phosphorus.

Paramagnetism
The elements high in available 2+ valence electrons, calcium, iron and magnesium in particular contribute to paramagnetism in soil which aid in cation exchange capacity.

pH
The calcium and magnesium in high quality has the ability to neutralise pH in soils, in effect acting as a liming agent

Spreading / applying dust in Agriculture
Rock Dust can be applied to soil either via hand application, via Broadcast spreader or fertigation. Where possible the rockdust can be worked into the ground either physically or by using water to wash in.

Rate of Application
In some soils which display poor levels of nutrients, application rates of 10 tonnes per hectare are required. In Australia, namely the Riverland, Riverina, Langhorne Creek, Barossa and Mclaren Vale regions, rates are 3 - 5 tonnes per hectare. In a garden application, this might equate to 400 grams per square metre.

Rockdust is also the limestone-based product sprayed on walls inside underground coal mines to keep coal dust levels down. This is to prevent coal dust explosions and also to prevent the incidence of black lung disease. (Disambiguation is required here)

History

Rockdusting, also known as soil remineralization was mentioned in the 19th century book Bread From Stones by chemist Julius Hensel.

In the 20th century, rockdusting was popularized by science writers John D. Hamaker, Larry Ephron, Alden Bryant, Don Weaver, Harvey Lisle, Arden Andersen and Dr. Lee Klinger.

See also

• Organic farming
• Rock flour
• Soil conditioner
• Organic fertilizer
• John D. Hamaker

External links

• Seer Centre
• BBC News report
• Scotland on Sunday report
• Remineralize The Earth