About

Precise irrigation is critical for maximizing yield while conserving resources. This calculator estimates the Crop Evapotranspiration (ET_c), which represents the water loss due to evaporation from soil and transpiration from plants. The tool applies the FAO 56 standard method by combining reference evapotranspiration (ET_o) with specific Crop Coefficients (K_c). These coefficients vary significantly based on the plant's growth stage - initial, development, mid-season, or late-season. Farmers and gardeners use these figures to program irrigation schedules, preventing both water stress and root rot caused by over-watering.

Formulas

The core calculation follows the FAO Penman-Monteith equation simplification:

ET_c = ET_o × K_c

To convert the depth of water (mm) to volume (Liters) for a specific area:

Volume = ET_c × Area (m²)

Note: 1 mm on 1 m² equals 1 Liter.

Reference Data

Crop Type	K_c Initial	K_c Mid-Season	K_c End
Tomato	0.6	1.15	0.80
Potato	0.5	1.15	0.75
Maize (Corn)	0.3	1.20	0.60
Wheat	0.3	1.15	0.30
Onion (Dry)	0.7	1.05	0.75
Citrus	0.7	0.65	0.70
Lawn Grass	0.9	0.95	0.95

Frequently Asked Questions

ETo is the rate of water loss from a standard reference surface (usually grass) based on local weather conditions like temperature, humidity, wind, and solar radiation. You can usually find this value in local weather reports or agricultural bulletins.

"Initial" is planting to 10% ground cover. "Development" is 10% cover to effective full cover. "Mid-season" is flowering/fruiting. "Late" is ripening/harvest.

Many crops, when fully developed, have a leaf area index large enough to transpire more water than the reference grass surface, necessitating a coefficient greater than 1.

No. This calculates the "Gross Irrigation Requirement". You must subtract effective rainfall from this result to determine the "Net Irrigation Requirement" (how much you actually need to add).