Soil Management

Storing Polyphosphates

Robert Mullen, Ph.D.

Robert Mullen

Robert Mullen, Ph.D.


Director of Agronomy

To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.

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John Walker
Nutrien | Engineer

Not only has the weather this spring affected farmers’ ability to get crops in the ground, it has also created situations where ag suppliers have products that did not make it to the field for application. A common question is how do I manage my storage of polyphosphates?

Briefly, polyphosphates are created by binding orthophosphates together into longer chain phosphate molecules. This allows the phosphate to stay in solution at higher concentrations of phosphorus. Temperature increases of the polyphosphate solution will cause degradation of the polyphosphate molecules into orthophosphates. This can create precipitation of solids in the solution, which will settle in the bottom of the storage container.

Table 1. Rate of conversion of polyphosphate to orthophosphate as impacted by solution temperature.

Here are a few things to remember when managing your polyphosphates in storage:

  • Store polyphosphates in lighter colored storage containers. That will help keep product temperature down compared to darker storage containers.
  • Do not agitate or circulate your polyphosphates when air/product temperatures are high. This can actually increase the temperature of the solution.
  • Monitor degradation of polyphosphates to help with management decisions.
    • Ideally, samples should be collected from the top, middle, and bottom of the container.
    • Once samples are collected refrigerate them immediately.
    • Samples should be shipped overnight to determine orthophosphate content (do not use two- or three-day shipping — that can allow the sample to get too warm). Ideally, samples should be shipped cool in an insulated container.
  • If the analysis reveals the polyphosphate concentration is approaching 60 percent (orthophosphate is approaching 40 percent), add fresh polyphosphate to the container. If the analysis reveals polyphosphate concentration is approaching 65 percent, ordering additional polyphosphate (to be added to the container) is recommended before the concentration of polyphosphate gets too low.
  • If polyphosphate concentration dips below 60 percent, solids are likely to precipitate in the solution.
  • Once precipitated, solids will not go back into solution when fresh polyphosphate is added.
  • Containers that have access points 18-24 inches off the bottom of the tank can be used to decant polyphosphate (free of solids) out of the tank.
  • Obviously, try to move the polyphosphate as soon as possible.