Introducing PLATO, the Phosphorus Loss Assessment Tool for Ontario

rill erosion on a steeply sloped field

Jake Munroe, Soil Management Specialist (Field Crops), OMAFRA

Keeping soil covered and minimizing erosion is a key principle of soil health. Maximizing the efficiency of crop nutrient uptake and minimizing losses are the foundation of 4R Nutrient Stewardship. When combined, these principles form the basis of a new online tool from OMAFRA called PLATO (Phosphorus Loss Assessment Tool for Ontario).

PLATO is a calculator that you can use to estimate the risk of phosphorus loss on your farm. It’s part of the newly re-vamped AgriSuite and uses your specific soil, crop and nutrient application information to provide a risk rating and options to improve your score.

Whether you’re considering a new way to apply fertilizer or manure, or you’d just like to know how you compare to your neighbours, PLATO provides answers.

How does it work?

You provide your county and geotownship, along with your soil series, soil texture and a soil test phosphorus value. Next, you select a crop type, tile drainage system and spacing details, and an estimate of erosion. Erosion can be calculated quickly by providing a maximum slope and basic tillage information or estimated more accurately by using the new Water Erosion Potential Map in AgMaps.

Figure 2. Screenshot of PLATO material application page, showing application details for a Mid-August application of liquid dairy manure.

Together, this information is used to calculate a Field Characteristic Index, which represents the risk of phosphorus loss based on inherent field characteristics such as runoff, erosion and phosphorus soil test. The Field Characteristic Index for a coarse-textured, flat, moderate soil test field is likely to be lower than for a high fertility, erodible soil, such as the one pictured in Figure 1.

Figure 1. Rill erosion in a highly erodible field. Water erosion acts as a transport mechanism for phosphorus and is reflected in the Field Characteristic Index in PLATO.











A 4R example

PLATO allows you to enter fertilizer or organic amendment applications. In the example in Figure 2, I plan to apply 4,000 gal/ac of liquid dairy manure in advance of a corn crop for the following season. The manure will be applied in mid-August by tanker and incorporated within two days. With this manure application, the Application Loss Index is only 0.6 and the overall PLATO score, or Phosphorus Index, is rated as very low (Figure 3). This is an example of a very good practice – the risk of phosphorus loss in the summer is low, especially if the manure is incorporated.





Figure 3. Summary of Field Characteristic, Phosphorus Loss Index and Total Phosphorus Index values for a late summer application of liquid dairy manure.

Application practices to avoid

If, 4,000 gallons/acre was applied on January 15th, on bare soil without incorporation, the risk increases substantially (Figure 4). Phosphorus applied late in the fall or winter is at a higher risk of loss, since there’s more runoff and tile flow in the non-growing season. Manure that’s surface-applied on frozen ground is at the highest risk of running off and this practice should be avoided.

Figure 4. Summary of Field Characteristic, Phosphorus Loss Index and Total Phosphorus Index values for a winter application of liquid dairy manure.

Putting the pieces together

PLATO can help you find ways to minimize phosphorus loss from your field. You can try scenarios to adjust the timing and placement of fertilizer or manure applications, or compare how reduced tillage practices can minimize the risk of soil erosion and Phosphorous runoff.

Try it for yourself

To use PLATO, visit the updated AgriSuite site at

While you’re there, take a look at the other new calculators, including the Crop Nutrient Calculator and the Organic Amendment Calculator. They’ve been designed using Ontario data to help you develop crop nutrient recommendations and determine nutrient values for a wide range of organic amendments.

This project was funded in part through the Canadian Agricultural Partnership (the Partnership), a federal-provincial-territorial initiative.