Ontario Corn Nitrogen Calculator

The Ontario Corn Nitrogen Calculator can be accessed by clicking the icon below.

(this is the same tool previously posted on gocorn.net)

Simple Summary

  • The Ontario Corn Nitrogen Calculator provides a recommendation for the most economical rate of nitrogen (N) for a corn field.
  • This recommendation is an estimate of the most economical rate of N based on a database of over 40 years of Ontario corn N response data and is driven by factors that had a strong impact on optimum N rates in those trials, including:
    • soil texture
    • whether the field was in Eastern Ontario
    • yield potential
    • heat units
    • previous crop
  • Recommendations are adjusted for:
    • price ratio of nitrogen relative to corn price
    • deductions for starter N and manure N credits
    • sidedress application timings

The Corn Nitrogen Calculator

Ontario Corn Nitrogen recommendations are derived from the Ontario corn nitrogen database which contains over 40 years of Ontario corn nitrogen yield response data. Current recommendations were released in 2006. Nitrogen response curves in the database were fitted to quadratic-plateau models and the optimum N rate for each trial was determined. The factors in the dataset that had the greatest impact on optimum N rate were used to develop a model to estimate N requirements for individual fields (Fig. 1).

Figure 1. Screenshot of Ontario Corn Nitrogen Calculator.

N Calculator Factors

Soil Texture

Base N requirements are provided by soil texture. Based on relationships in the Ontario N database, different soil textures have different base requirements. Base requirements also vary depending if the field is in Southwestern and Central Ontario or Eastern Ontario (Table 1).

Table 1. Base rate nitrogen recommendation by soil texture

Soil TextureBase N Requirements
Southwestern and Central OntarioEastern Ontario
Clay, Heavy clay475311
Clay loam364011
Loamy sand41461719
Sandy loam34381719
Sandy clay, Sandy clay loam38431719
Silt loam182011
Silty clay loam323611
Silty clay444911

Eastern Ontario

In the Ontario N database, trials in Eastern Ontario (defined as the counties of Frontenac and Renfrew and all counties east) generally had lower optimum N rates than trials in Southwestern or Central Ontario. The reasons why are not fully understood, but lower base recommendations for Eastern Ontario are included to reflect this (Table 1).

Yield Potential

As the yield potential (e.g. average yield over the past 5 years) of a field increases, so does the estimated optimum N rate. Based on relationships in the Ontario N database, N recommendations change by 0.76 lb-N/ac per bushel (13.7 kg-N/ha per tonne) of corn yield. This adjustment is made in addition to the base amount of N calculated by the other factors.

Heat Units

The Ontario corn nitrogen database suggests that as the heat unit rating of a field increases, so does the optimum N rate. The base recommendation in the N calculator is for 2,800 CHU and recommendations are adjusted 3.7 lb-N/ac (4.1 kg-N/ha) for every 100 CHU above or below 2,800.

Previous Crop

Optimum N rate is influenced by the amount and type of residue and nitrogen credits from previous crops.

Previous crops with high amounts of residue (e.g. corn, cereals with straw returned), and especially those with high C:N ratios, can temporarily immobilize N in the microbes that proliferate to break down residue during the following corn growing season. Previous crops with low amounts of residue (e.g. soybeans or edible beans) may immobilize little N. If N is immobilized from previous crops, less is available for crop uptake and optimum fertilizer N rates are higher.

Clover cover crops and perennial forages including legumes can mineralize N as they are decomposed during the following corn growing season. These crops in particular release N in good synchrony for corn uptake the following year, which not all crops or cover crops do. This extra N results in lower optimum fertilizer N rates.

Nitrogen recommendations incorporate previous crops to account for differences in immobilization and N credits (Table 2). 

Table 2. Nitrogen adjustments for various previous crops.

Previous CropAdjustment
Grain corn00
Silage corn-12-14
Cereals (straw removed)-11-12
Cereals (straw not removed)00
Dry edible beans-27-30
Clover cover crop (plowed)-73-82
Clover cover crop (no-till)-60-67
Perennial forage – less than one-third legume00
Perennial forage – one-third to half legume-49-55
Perennial forage – over half legume-98-110


Nitrogen Fertilizer and Corn Prices

Nitrogen fertilizer and corn prices are included to adjust recommendations for the relative price ratio between the two. As N becomes more expensive relative to corn, the most economic N rates declines. Recommendations are adjusted slightly downwards.

Deductions for Starter N or Manure N

Deductions for starter N or manure N are made from the total recommendation as these count towards the total N recommendation. Manure N credits are not calculated in the N calculator but can be estimated using the organic amendment tool in AgriSuite (search internet for “OMAFRA Agrisuite”).

Sidedress Timing Credits

Sidedress timing credits are made for N applications that are delayed until traditional sidedress time (e.g. V4-V6, or knee high stage). Based on current data in the Ontario corn nitrogen database, there is no sidedress credit in Eastern Ontario. If you are in Southwestern or Central Ontario, sidedress credit depends on soil texture.

  • For “sand” soil textures (sand, loamy sand) there is no sidedress credit

(sidedress N recommendation is the same as preplant N recommendation)

  • For “sandy” soil textures (sandy clay, sandy clay loam, sandy loam) there is a 10% sidedress credit (sidedress N recommendation is 90% of preplant N recommendation)
  • For all other soil textures, there is a 20% sidedress credit (sidedress N recommendation is 80% of preplant N recommendation)

Sidedress credits are summarized in Table 3.

Table 3. Sidedress credit by soil texture in Southwestern and Central Ontario.  

Soil TextureSidedress N Recommendation Adjustment
(% of preplant N recommendation)
Sand, loamy sand100%
Sandy clay, sandy clay loam, sandy loam90%
Clay, clay loam, loam, silt loam, silty clay, silty clay loam80%