Phosphate rock

Natural rock rich in calcium phosphate (apatite), mined and ground for direct application to the soil.

Characteristics

Analysis published by Ecoagro (Mexico) for its rock of marine sedimentary origin: phosphorus 26% (as oxide), calcium oxide 34.9%, silicon 20%, iron oxide 3.08%, zinc 95 ppm, moisture 5%.
Advantages put forward by the maker: high reactivity, gradual release of phosphorus, supply of phosphorus, calcium and silicon, no added chemicals, blends well into compost, compatible with other fertilisers.
The maker states that its product is OMRI listed and Certimex certified for organic farming.
According to FAO, phosphate rock works best in acid soils rich in organic matter with good rainfall, and the finer and more reactive the rock, the better.
Phosphorus is released as the rock dissolves in the soil: it is not soluble like manufactured phosphates.

Role in the preparation: Worked into the soil (FAO advises near sowing in very acid soils, 4–8 weeks before in less acid soils), or added to compost and bokashi.

Caution: Fine dust: wear a mask. Ask the supplier for a heavy-metal analysis (cadmium in particular), which varies with the deposit.

Sources: Ecoagro (Guamúchil, Sinaloa, México) — ficha técnica «Roca fosfórica» · FAO — Use of phosphate rocks for sustainable agriculture (Fertilizer and Plant Nutrition Bulletin 13, 2004)

Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.