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Calcimator

Variable Rate Fertilizer Calculator

Application map from soil test zones and yield goals.

Inputs

%

Results

N rate (lbs/acre)

190

P₂O₅ rate (lbs/acre)

97

K₂O rate (lbs/acre)

104

Total N credits (lbs/acre)30
OM N credit (lbs/acre)30
P₂O₅ maintenance (lbs/acre)74
P₂O₅ buildup (lbs/acre/yr)23
K₂O maintenance (lbs/acre)54
K₂O buildup (lbs/acre/yr)50
P sufficient? (1=yes)0
K sufficient? (1=yes)0
Est. cost per acre ($)$214.03
Total zone cost ($)$8,561.00
How to Use This Calculator
  1. Enter Zone Size (acres) and Yield Goal (bu/acre) for the management zone being calculated.
  2. Enter Soil Test P (ppm), Soil Test K (ppm), and Soil OM (%) from lab results.
  3. Set N Factor (lbs N/bu), P₂O₅ Removal (lbs/bu), and K₂O Removal (lbs/bu) for your crop.
  4. Enter Previous Crop N Credit and Manure N Credit if applicable to reduce synthetic N rates.
  5. Review Recommended N, P₂O₅, and K₂O rates (lbs/acre) — export these values to your precision ag controller for zone-specific application.

How the result changes with Yield goal (bu/acre)

Yield goal (bu/acre)N rate (lbs/acre)P₂O₅ rate (lbs/acre)K₂O rate (lbs/acre)
50254164
1751638797
325328143138
450465189172

What each input means

Zone size (acres)
Acreage of this management zone.
Yield goal (bu/acre)
Realistic yield target for this zone.
Soil test P (ppm)
Bray-1 or Mehlich-3 phosphorus in ppm.
Soil test K (ppm)
Exchangeable potassium in ppm.
Organic matter (%)
Soil organic matter percentage. Higher OM provides more N credit.
N factor (lbs N/bu)
Nitrogen needed per bushel of yield goal (corn = 1.0-1.2).
P₂O₅ removal (lbs/bu)
P₂O₅ removed per bushel harvested (corn = 0.37, soy = 0.80).
K₂O removal (lbs/bu)
K₂O removed per bushel harvested (corn = 0.27, soy = 1.40).
Previous crop N credit (lbs/acre)
N credit from previous legume crop (soybeans = ~40 lbs).
Manure N credit (lbs/acre)
Plant-available N from manure applied.
P sufficiency target (ppm)
Soil test P level considered sufficient (typically 20-30 ppm).
K sufficiency target (ppm)
Soil test K level considered sufficient (typically 150-200 ppm).

What each result means

N rate (lbs/acre)
Recommended nitrogen application rate for this zone.
P₂O₅ rate (lbs/acre)
Recommended phosphate rate (maintenance + buildup if needed).
K₂O rate (lbs/acre)
Recommended potash rate (maintenance + buildup if needed).
Total N credits (lbs/acre)
Sum of all nitrogen credits applied.
OM N credit (lbs/acre)
Estimated N credit from soil organic matter.
P₂O₅ maintenance (lbs/acre)
Phosphate needed to replace crop removal.
P₂O₅ buildup (lbs/acre/yr)
Annual phosphate buildup rate to reach sufficiency over 4 years.
K₂O maintenance (lbs/acre)
Potash needed to replace crop removal.
K₂O buildup (lbs/acre/yr)
Annual potash buildup rate to reach sufficiency over 4 years.
P sufficient? (1=yes)
Whether phosphorus soil test is at or above sufficiency.
K sufficient? (1=yes)
Whether potassium soil test is at or above sufficiency.
Est. cost per acre ($)
Estimated fertilizer cost per acre at current prices.
Total zone cost ($)
Total fertilizer cost for this management zone.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Zone size (acres) = 40, Yield goal (bu/acre) = 200, Soil test P (ppm) = 15, Soil test K (ppm) = 150 = 12 input(s) provided
  2. Calculate N rate
    N rate
    190 = 190
  3. Calculate P₂O₅ rate
    P₂O₅ rate = soilTestP >= pSufficiency
    97 = 97
  4. Calculate K₂O rate
    K₂O rate = soilTestK >= kSufficiency
    104 = 104
  5. Calculate Total N credits
    Total N credits = previousCropNCredit + manureNCredit + omNCredit
    30 = 30
  6. Calculate OM N credit
    OM N credit
    30 = 30

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