Agriculture Reference
In-Depth Information
Black mica, also known as biotite, refers to a class of micas, rather than to
a specific chemical formula. These micas contain variable amounts of po-
tassium, usually several percent, in a form that is quite available to plants in
biologically active soils. If you need to add potassium and have ready access
to inexpensive sources of biotite, it can be an effective soil amendment. Un-
fortunately, biotite fertilizers can be hard to find. Also, at least one European
study found that one source of biotite included barium and strontium that
could be taken up by horticultural crops in sufficient concentrations to pos-
sibly be toxic to humans.
More effective and cost-effective sources of potassium include the follow-
ing: Sulfate of potash-magnesia (sul-po-mag or langbeinite) is a rich source
of potassium that also supplies sulfur and magnesium. Wood ashes are rich
in potassium and, when used cautiously (see page 92 ) , can be beneficial,
especially on acidic soils. Do not use wood ashes if the soil pH is 6.5 or above.
Potassium sulfate is a good source of rapidly available potassium, but en-
sure that your source meets organic certification standards. Some organic
certifying organizations prohibit it altogether. One form of potassium sulfate
fertilizer is created industrially using sulfuric acid and is not suitable for
organic growers. Natural potassium sulfate is mined or extracted through
evaporation of water from saline lakes.
Potassium chloride contains 60 percent potash that is rapidly available to
plants. It also contains a high amount of chloride, so it's not a good idea to
use it frequently or in large doses. The U.S. National Organic Program allows
the use of potassium chloride only if it is “derived from a mined source and
applied in a manner that minimizes chloride accumulation in the soil.” Before
applying potassium chloride, check with your organic certifying organization
to ensure you can use this material.
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