Market Farming

[Aaron Silverman <cgrowers AT pond.net>]

>    The US has about 40% of the world's supply of  mineral phosphorus and
>most of it is in Florida. So that is where rock phosphate comes from but it
>is where rock phosphate is converted to other phosphorus fertilizers as
>well.

Just a minor follow up on this point:
US supplies of rock phosphate comes from both Florida and North Carolina. 
NC phosphate is generally called hard rock phosphate, while Fla. product 
may be referred to as pebble phosphate, or even soft rock phosphate. 
These two forms have slightly different chemical formulas, and therefor 
react slightly differently in soil. They also have different Ca contents.

The following is quoted from Fertile Soil by Robert Parnes: "Colloidal 
rock phosphate is a mojor source of phosphorus in organic agriculture. 
When rock phosphate from Florida is mined, a very finely divided 
low-grade ore is removed by washing it away to a settling basin. After 
the water has evaporated, any sediment which has a phosphate content of 
20% or more is sold as an animal feed supplement, and the rest is 
marketed as colloidal phosphate for fertilizer use...Colloidal phosphate 
has about 2% available P compared to 11% for bone meal. Rock P has a 
variable amount of available P, although some is marketed with a 3% 
content." Note that colloidal P generally has 18% P value, but only 2% 
may be available in the soil water at any given time.

Aaron

Creative Growers
Aaron Silverman
88741 Torrence Rd.
Noti, Or. 97461
cgrowers AT pond.net
Quality Produce & Pastured Poultry