The same principle can be used in reverse to estimate a fertilizer N recommendation as follows:

Step 1: Determine crop need – based on expected yield and removal rate

Step 2: Use the estimate of soil nitrate levels

Step 3: About half of this available nitrate-N is retuned to the organic pool

Step 4: Amount mineralized from organic matter (as before in Step 2 and 3)

Step 5: N immobilized by crop residue (as before in step 6)

Step 6: Calculate N need (difference from above)

Step 7: Calculate N fertilizer need based on efficiency (usually about 50%)

Adjustments may need to be made to these estimates based upon environmental conditions that may cause greater than expected nitrogen losses. These conditions would be leaching of nitrate-N on sandy soils and denitrification when soils are saturated. Adjustments may also be required where release of N from soil organic matter may be higher or lower than average.

| Introduction | Nitrogen | Phosphorus | Potassium | Sulphur | Micronutrients | The Fertilizer Act and Quality Standards | Calculating Fertilizer Rates from Nutrient Recommendations | Fall/Spring Fertilizer Price Differences | Common Fertilizers and Their Characteristics | Fertilizer Recommendation Guidelines | Manure | Nitrogen Fixation | Soil pH and Salinity | Nutrient Management Plans | Manitoba Fertilizer Recommendation Guidelines Based on Soil Tests | Fertilizer Guidelines for Soil Tests | Developing Fertilizer Recommendations without a Soil Test | Developing a Fertilizer Recommendation Rate| Agronomically, Economically and Environmentally Sensible Target Yields |General Fertilizer Recommendations Without a Soil Test | References |

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