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Calcimator

Drought Management Calculator

Plan deficit irrigation strategy using FAO yield-response model to minimize yield and revenue loss when water supply is limited.

Inputs

%

Results

Water supply ratio (%)

56.7

Yield reduction (%)

49.8

Full ET requirement (acre-in)2,400
ET deficit (%)43.3
Expected yield (bu/acre)100.3
Yield loss (bu/acre)99.7
Projected revenue ($)$55,183.00
Revenue loss ($)$54,817.00
Water cost ($)$5,600.00
Net return ($)$49,583.00
Water productivity (bu/acre-in)6.27
Water saved (acre-in)1,224
Marginal value of water ($/acre-in)$52.71
Net Return Full100,117.65
How to Use This Calculator
  1. Enter Field size (acres), Full-season crop ET (in), and Available water (acre-in).
  2. Set Yield response factor (Ky), Max yield (bu/acre), and Crop price ($/bu).
  3. Adjust Water cost ($/acre-in), System efficiency (%) as needed.
  4. Review Water supply ratio (%) and Yield reduction (%).
  5. Use Full ET requirement (acre-in) and ET deficit (%) to inform your decision.

How the result changes with Field size (acres)

Field size (acres)Water supply ratio (%)Yield reduction (%)
50111.3100
1,7513.2100
3,2501.7100
4,5001.3100

What each input means

Field size (acres)
Total irrigated field area.
Full-season crop ET (in)
Total crop evapotranspiration for the full growing season.
Available water (acre-in)
Total water allocation for the season in acre-inches.
Yield response factor (Ky)
FAO yield response factor. Corn=1.25, wheat=1.05, soybean=0.85.
Max yield (bu/acre)
Expected yield under full irrigation.
Crop price ($/bu)
Expected market price per bushel.
Water cost ($/acre-in)
Cost per acre-inch of water applied (pumping + delivery).
System efficiency (%)
Irrigation application efficiency.

What each result means

Full ET requirement (acre-in)
Total water needed for full-season ET at field scale.
Water supply ratio (%)
Percentage of full ET requirement met by available supply.
ET deficit (%)
Fraction of ET not supplied.
Yield reduction (%)
Expected yield loss from water deficit using Ky factor.
Expected yield (bu/acre)
Projected yield under deficit irrigation.
Yield loss (bu/acre)
Bushels per acre lost compared to full irrigation.
Projected revenue ($)
Total crop revenue under deficit irrigation.
Revenue loss ($)
Revenue lost compared to full irrigation.
Water cost ($)
Total cost of water applied.
Net return ($)
Revenue minus water cost under deficit irrigation.
Water productivity (bu/acre-in)
Bushels produced per acre-inch of water applied.
Water saved (acre-in)
Water saved compared to full irrigation.
Marginal value of water ($/acre-in)
Revenue gain from one additional acre-inch of water.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Field size (acres) = 100, Full-season crop ET (in) = 24, Available water (acre-in) = 1600, Yield response factor (Ky) = 1.15 = 8 input(s) provided
  2. Calculate Water supply ratio
    Water supply ratio = min(1, netWaterAvailable / max(1, fullEtRequirement))
    56.7 = 56.7
  3. Calculate Yield reduction
    Yield reduction = min(1, yieldResponseKy * deficitFraction)
    49.8 = 49.8
  4. Calculate Full ET requirement
    Full ET requirement = fullSeasonEtIn * fieldAcres
    2400 = 2400
  5. Calculate ET deficit
    ET deficit = 1 - supplyRatio
    43.3 = 43.3

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

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