Corn Fertilizer Rates in Ontario
Nitrogen, phosphate and potash guidance for corn in Ontario, taken from the OMAFRA Agronomy Guide for Field Crops (Publication 811) soil-test sufficiency tables.
Typical Ontario yield goal: 175 bu/ac. Micronutrient to watch: Zn.
Nitrogen: how the rate is built
Ontario sizes corn nitrogen from three pieces: a base requirement set by soil texture, plus a yield-driven component, minus a credit for the previous crop.
N (kg/ha) = base N for your soil + (yield in t/ha × 13.6) − previous-crop credit
Base nitrogen by soil texture
| Soil texture | Base N | Base N |
|---|---|---|
| Clay / heavy clay | 53 kg/ha | 47 lb/ac |
| Clay loam | 40 kg/ha | 36 lb/ac |
| Loam | 32 kg/ha | 29 lb/ac |
| Silt loam | 20 kg/ha | 18 lb/ac |
| Silty clay loam | 36 kg/ha | 32 lb/ac |
| Silty clay | 49 kg/ha | 44 lb/ac |
| Sandy loam | 38 kg/ha | 34 lb/ac |
| Loamy sand | 46 kg/ha | 41 lb/ac |
| Sand | 52 kg/ha | 46 lb/ac |
| Sandy clay loam | 43 kg/ha | 38 lb/ac |
Previous-crop nitrogen credits
What grew last year matters. A ploughed-down legume can supply most of a corn crop's nitrogen.
| Previous crop | Credit | Credit |
|---|---|---|
| None / fallow | 0 kg/ha | 0 lb/ac |
| Grain corn | 0 kg/ha | 0 lb/ac |
| Cereals (wheat/barley/oats) | 12 kg/ha | 11 lb/ac |
| Soybeans | 30 kg/ha | 27 lb/ac |
| Dry edible beans | 30 kg/ha | 27 lb/ac |
| Red clover (plowed down) | 82 kg/ha | 73 lb/ac |
| Alfalfa / forage (½+ legume) | 110 kg/ha | 98 lb/ac |
| Alfalfa / forage (⅓–½ legume) | 55 kg/ha | 49 lb/ac |
Phosphate (P₂O₅) by soil test
Find your Olsen P value and read across.
| 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 |
Potash (K₂O) by soil test
| 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 |
Timing and placement
Apply most N in spring — pre-plant, pre-emerge, or side-dress before the corn is 30 cm (12 in.) tall. Fall N is discouraged (leaching/denitrification losses). Place starter P (and some K) in a band 5 cm beside and 5 cm below the seed; 10–15 kg/ha P₂O₅ with the seed is highly efficient. Incorporate broadcast urea to stop volatilization.
No soil test?
Without one you are guessing. As a fallback, corn removes roughly 6.6 kg P₂O₅ and 4.8 kg K₂O per tonne of grain, so replacement rates can hold soil levels steady — but replacement is not a recommendation. It cannot tell you whether you are already at 20 ppm and wasting money, or at 5 ppm and losing yield. Get a test from an accredited lab.
Cutting the fertilizer bill on corn
- Credit manure before you buy anything — see available nutrients in manure and compost.
- Credit the nitrogen carried in MAP or DAP against your N requirement.
- Stop applying phosphate and potash where the soil test says no response is expected.
- Compare products on cost per unit of nutrient, not price per tonne.
Related guides
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