Phosphorus can be a Limiting Nutrient in Canadian Organic Soils

Phosphorus is very important for the growth and development of the crop.

  • Stimulates early season growth
  • Promotes seed production
  • Promotes the growth of deeper and stronger roots
  • Ensures a competitive crop
  • Reduces weed, disease and insect pressure
  • Hastens plant maturity
  • Drives yield

Phosphorus is necessary early in the season, but is also required throughout the plants lifecycle. Phosphorus deficiency leads to stunted growth, purpling of leaves, inhibition of flowering and root system development.

Over fertilization with phosphorus (mono-ammonium phosphate, di-ammonium phosphate) is common. Early excessive conventional phosphorus applications can be toxic and harm the seedling leading to reduced germination and stunted early growth. Excess of phosphorus also interferes with elemental uptake of iron, manganese and zinc. Rock phosphate is safe to apply with the seed, does not burn the crop and supplies rock phosphate slowly over time, matching crop requirements. Residual phosphorus also provided extended feeding for approximately 3 years after application.

Agvise tests the soil for Olsen-Bicarbonate phosphorus in ppm. Their thresholds are as follows:

  • Very Low: 1-3 ppm
  • Low: 4-7 ppm
  • Medium: 8-11 ppm
  • High: 12-15 ppm
  • Very High: > 15 ppm

Soil sampling of 35 organic fields indicated that 43 percent of fields were low to very low in soil phosphorus in the spring.

In organic production, there are limited amendments available to supply phosphorus to the soil. Fertoz Rock phosphate is an excellent (non-saline) supply of soil phosphorus containing the highest level of total phosphate (>20%) and available phosphate (>7%) and also provides a good source of calcium.