Not All Phosphate is Made the Same

Organic and conventional producers are seeking natural high quality sustainable solutions to their phosphorus deficiencies. Rock Phosphate is the organic input option with the highest level of total phosphate. Although it is a direct mined source; which can be certified for use in organic production – not all rock phosphate is natural and effective. When seeking rock phosphate product, verify quality parameters to guarantee the health of your soil, the environment and your crop.

Verify the phosphate content.

Higher total and available phosphorus levels require lower application rates. As a producer with a long-term vision, total phosphorus is important. Phosphorus deriving from naturally mined rock phosphate tends to stay in the soil where it is placed (rather than leached from the soil like commercial fertilizers).   With high levels of total phosphorus, you can assure steady phosphorus availability over time. Available phosphorus levels provide an indication of expected near term phosphorus availability  under typical soil conditions.

Use a fertilizer product that will work in your equipment, or consider custom application.

Rock Phosphate is excavated and pulverized. Product can then be processed further through additional crushing to create a soluble solution for fertigation. Product can be granulated for use in a seeder or fertilizer spreader.

Purchase product through a supplier that you can trust.

Transparency and traceability are important! The supplier should be willing to share information with you on the product and its origin. The product should be fully traceable back to its source.

Product purity is important.

Rock phosphate is mainly comprised of phosphate, calcium oxide and silica. Salt levels are typically low, making rock phosphate an excellent alternative to conventional fertilizer in saline soils. Minute levels of micronutrients can be present. Manganese and iron are common and can be beneficial to soils limiting in these nutrients. Because rock phosphate is typically applied at 3x the rate of conventional phosphate fertilizer, an excess in a single micronutrient can be detrimental to the soil and health of your crop. As example, iron in rock phosphate can be as high as 10%. High application rates of 2 lbs/ac Fe are recommended in severely iron deficient soil. Iron toxicity can be induced even at very low iron application rates. A product containing 15% iron, applied at 200 lbs/acre provides 20 lbs/acre of iron to the soil creating fundamental nutrient imbalance and long lasting injury to your soil and crop.

Verify the analysis of your product for impurities. Contaminants such as heavy metals can be present in the product. Organic standards in Canada and The United States vary in terms of allowable levels of heavy metals. Canadian organic producers cannot use products containing over 90 mg Cd/kg P. Cadmium, lead, arsenic, barium and mercury at high levels are toxic to soil microbes and poses a health risk to humans and wildlife.  Heavy metals tend to concentrate in tailing ponds.  Ask your rock phosphate supplier about the origin or the product; is it naturally mined or derived from tailings ponds?

References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1389745/

http://archive.lib.msu.edu/tic/tgtre/article/1999feb1a.pdf