Long-Lasting Phosphorus and Calcium
Soft rock phosphate, also known as colloidal phosphate, is a clay material surface mined from the old settling basins of former hard phosphate rock mining operations in Florida. It contains about 20 percent P2O5 as well as over 25 percent lime and other trace minerals, and has 18% phosphorus and 15% calcium as well as trace elements.
Key things we want you to know
How to apply: Till it in, ideally directly under the seed or transplant, since annuals take up to 60% of their phosphate in the first weeks.
Why soft rock: It is insoluble in water, so it stays put and does not leach.
Rate: About two tons per acre together with other amendments.
It is a very fine material but can be applied with all common fertilizer spreaders. Natural phosphate stays where it is put and does not move or dissolve into the soil solution. Unlike chemically made phosphates, soft rock phosphate is insoluble in water and will not leach away, so it is long-lasting.
Suggested Application
- Place it at the root: An annual plant takes up to 60 percent of its total phosphate needs in the first few weeks of life, so soft rock phosphate used directly under the seed or transplant at planting time is the best method, especially in low-acid or high-alkaline soils. It is still beneficial in slightly acid to neutral soils.
- Work it in: It needs to be plowed under or tilled into the soil.
- Rate: About two tons per acre together with other amendments.
Information derived from www.dirtdoctor.com.