CropGPT › How to Read Your Ontario Soil Test
How to Read Your Ontario Soil Test
Your soil test reports phosphorus and potassium in parts per million (ppm). OMAFRA Publication 811 converts those ppm values into a fertilizer rate using sufficiency tables — reproduced in full below, for every major Ontario field crop.
The two numbers that drive your rate
Ontario uses a sufficiency approach, not crop removal. The question is not "how much did the crop
take away" but "at this soil test level, will added fertilizer actually pay?" As soil-test values rise, the
recommended rate falls to zero — because there is already enough in the soil.
The economic sweet spots. Ontario research found starter fertilizer
(20–30 lb P₂O₅/ac) gave the most economic response when Olsen P was between 12 and 18 ppm.
The same held for potassium between 100 and 130 ppm.
Response ratings explained
| Rating | Meaning |
|---|
| High response | Fertilizer will almost certainly increase yield. Apply the full rate. |
| Medium response | A yield response is likely but smaller. Apply the recommended rate. |
| Low response | A response is possible but unreliable. Starter placement only. |
| Rare response | A response is unlikely. Applying is generally not economic. |
| No response | No yield benefit expected. Do not apply. |
Sufficiency tables by crop
Find your soil-test ppm in the left column and read across for the recommended rate.
Corn
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 110 kg/ha | 98 lb/ac | High response |
| 3–5 ppm | 100 kg/ha | 89 lb/ac | High response |
| 5–7 ppm | 90 kg/ha | 80 lb/ac | High response |
| 7–9 ppm | 70 kg/ha | 62 lb/ac | High response |
| 9–12 ppm | 50 kg/ha | 45 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–20 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 20–30 ppm | 20 kg/ha | 18 lb/ac | Low response |
| 30–60 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 60 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 170 kg/ha | 152 lb/ac | High response |
| 15–30 ppm | 160 kg/ha | 143 lb/ac | High response |
| 30–45 ppm | 140 kg/ha | 125 lb/ac | High response |
| 45–60 ppm | 110 kg/ha | 98 lb/ac | High response |
| 60–80 ppm | 80 kg/ha | 71 lb/ac | Medium response |
| 80–100 ppm | 50 kg/ha | 45 lb/ac | Medium response |
| 100–120 ppm | 30 kg/ha | 27 lb/ac | Medium response |
| 120–150 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 150–250 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 250 ppm | 0 kg/ha | 0 lb/ac | No response |
Soybean
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 80 kg/ha | 71 lb/ac | High response |
| 3–5 ppm | 60 kg/ha | 54 lb/ac | High response |
| 5–7 ppm | 50 kg/ha | 45 lb/ac | High response |
| 7–9 ppm | 40 kg/ha | 36 lb/ac | High response |
| 9–12 ppm | 30 kg/ha | 27 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–30 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 30–60 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 60 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 120 kg/ha | 107 lb/ac | High response |
| 15–30 ppm | 110 kg/ha | 98 lb/ac | High response |
| 30–45 ppm | 90 kg/ha | 80 lb/ac | High response |
| 45–60 ppm | 80 kg/ha | 71 lb/ac | High response |
| 60–80 ppm | 60 kg/ha | 54 lb/ac | Medium response |
| 80–100 ppm | 40 kg/ha | 36 lb/ac | Medium response |
| 100–120 ppm | 30 kg/ha | 27 lb/ac | Medium response |
| 120–150 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 150–250 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 250 ppm | 0 kg/ha | 0 lb/ac | No response |
Winter wheat
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 70 kg/ha | 62 lb/ac | High response |
| 3–5 ppm | 60 kg/ha | 54 lb/ac | High response |
| 5–7 ppm | 50 kg/ha | 45 lb/ac | High response |
| 7–9 ppm | 30 kg/ha | 27 lb/ac | High response |
| 9–12 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–20 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 20–30 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 30–40 ppm | 0 kg/ha | 0 lb/ac | Low response |
| over 40 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 50 kg/ha | 45 lb/ac | High response |
| 15–30 ppm | 40 kg/ha | 36 lb/ac | High response |
| 30–45 ppm | 30 kg/ha | 27 lb/ac | High response |
| 45–60 ppm | 20 kg/ha | 18 lb/ac | High response |
| 60–80 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 80–100 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 100–120 ppm | 20 kg/ha | 18 lb/ac | Low response |
| 120–150 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 150 ppm | 0 kg/ha | 0 lb/ac | Rare response |
Spring grain
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 110 kg/ha | 98 lb/ac | High response |
| 3–5 ppm | 100 kg/ha | 89 lb/ac | High response |
| 5–7 ppm | 90 kg/ha | 80 lb/ac | High response |
| 7–9 ppm | 70 kg/ha | 62 lb/ac | High response |
| 9–12 ppm | 50 kg/ha | 45 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–20 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 20–25 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 25–40 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 40 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 90 kg/ha | 80 lb/ac | High response |
| 15–30 ppm | 80 kg/ha | 71 lb/ac | High response |
| 30–45 ppm | 70 kg/ha | 62 lb/ac | High response |
| 45–60 ppm | 50 kg/ha | 45 lb/ac | High response |
| 60–80 ppm | 40 kg/ha | 36 lb/ac | High response |
| 80–100 ppm | 30 kg/ha | 27 lb/ac | Medium response |
| 100–120 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 120–150 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 150–180 ppm | 0 kg/ha | 0 lb/ac | Low response |
| over 180 ppm | 0 kg/ha | 0 lb/ac | Rare response |
Oats
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 70 kg/ha | 62 lb/ac | High response |
| 3–5 ppm | 60 kg/ha | 54 lb/ac | High response |
| 5–7 ppm | 50 kg/ha | 45 lb/ac | High response |
| 7–9 ppm | 30 kg/ha | 27 lb/ac | High response |
| 9–12 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–20 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 20–40 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 40 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 70 kg/ha | 62 lb/ac | High response |
| 15–30 ppm | 50 kg/ha | 45 lb/ac | High response |
| 30–45 ppm | 40 kg/ha | 36 lb/ac | High response |
| 45–60 ppm | 30 kg/ha | 27 lb/ac | High response |
| 60–80 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 80–100 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 100–120 ppm | 0 kg/ha | 0 lb/ac | Low response |
| over 120 ppm | 0 kg/ha | 0 lb/ac | Rare response |
Canola
Olsen phosphorus (P) → recommended P₂O₅| Soil test | P₂O₅ rate | P₂O₅ rate | Expected response |
|---|
| 0–3 ppm | 70 kg/ha | 62 lb/ac | High response |
| 3–5 ppm | 60 kg/ha | 54 lb/ac | High response |
| 5–7 ppm | 50 kg/ha | 45 lb/ac | High response |
| 7–9 ppm | 30 kg/ha | 27 lb/ac | High response |
| 9–12 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 12–15 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 15–30 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 30–60 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 60 ppm | 0 kg/ha | 0 lb/ac | No response |
Ammonium-acetate potassium (K) → recommended K₂O| Soil test | K₂O rate | K₂O rate | Expected response |
|---|
| 0–15 ppm | 70 kg/ha | 62 lb/ac | High response |
| 15–30 ppm | 50 kg/ha | 45 lb/ac | High response |
| 30–45 ppm | 40 kg/ha | 36 lb/ac | High response |
| 45–60 ppm | 30 kg/ha | 27 lb/ac | High response |
| 60–80 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 80–100 ppm | 20 kg/ha | 18 lb/ac | Medium response |
| 100–120 ppm | 0 kg/ha | 0 lb/ac | Low response |
| 120–250 ppm | 0 kg/ha | 0 lb/ac | Rare response |
| over 250 ppm | 0 kg/ha | 0 lb/ac | No response |
Common questions
What is a good phosphorus level in Ontario soil?
Ontario research shows the most economic starter response when Olsen P sits between 12 and 18 ppm. Above roughly 30 ppm, phosphate applications rarely produce a yield response; above 60 ppm no response is expected.
What is a good potassium level in Ontario soil?
Potassium between 100 and 130 ppm is the range where starter potash typically pays. Above 150 ppm a response is unlikely, and above 250 ppm no response is expected.
Why does my US soil test not match Ontario recommendations?
OMAFRA guidelines are calibrated to the Olsen (sodium bicarbonate) phosphorus extraction. Mehlich-3 and Bray-P1, used widely in the United States, return different numbers that do not map onto Ontario tables.
How deep should I sample?
A consistent 15 cm (6 inch) depth, with 15 to 20 cores per composite sample, avoiding headlands, old manure piles and fence lines.
Need the labs? See our list of OMAFRA-accredited soil testing laboratories.
Related guides
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