Struvite’s potential as an alternative phos-phorus source for organic agriculture

Summary

Outcome
Depending on the process, normally 12-22% of P present in wastewater is recovered in struvite. The P in struvite is not water-soluble but soluble in weak organic acids, such as those present in root exudates. The quality and purity of the final product depends on the production process, but contaminant levels are generally very low.
Practical recommendations
• Given the nutrient content of struvite (5% N, 28% phosphate (P2O5), 10% Magnesium (Mg)) we recommend using it to provide P together with limited amounts of N and Mg.
• We recommend the use of struvite for crops with continuous need for P. Struvite slowly dissolves in the soil over time, especially when solubilised by root exudates, such as citrate, or under acidic conditions. In contrast to rock phosphate, it becomes available to the plant over time, even in alkaline soils.
• The maximum amount to apply corresponds to the expected P removal by the crop. The recommended doses are similar to any other P fertiliser.
• Struvite can be used in all crops (arable, horticultural, forage).
• The product is formulated in granules of about 1 to 3 mm in diameter, allowing the use of normal farm machinery.
• Since struvite releases P rather slowly, application before or at sowing is recommended. Struvite must be incorporated into the soil after broadcast application. Use of struvite in rows is also possible.