Kc (Crop Coefficient) Made Easy: From Kc Tables to a Practical Watering Plan
What Is Kc (Crop Coefficient)?
The crop coefficient (Kc) is a ratio used in irrigation science: it adjusts reference evapotranspiration (ET₀) to reflect a specific crop’s water needs. In simple terms: ETc = Kc × ET₀
Here, ETc is your crop’s actual water requirement. Reference evapotranspiration (ET₀) is the water loss expected from a well-watered grass surface. Kc translates that into the needs of your crop. Kc varies through a crop’s growing season: initial, development, mid-season, and late stages, because crop structure, shading, and canopy evolve over time.
Why Kc Matters
Matching water to crop needs: Kc ensures plants get neither too little nor too much water as they grow.
Seasonal accuracy: Using stage-specific Kc values helps avoid overwatering in early or late stages and supports peak production during mid-season.
Science-backed irrigation: FAO‑56 is an internationally recognized standard for calculating crop water needs.
Typical Kc Values for Common Crops
Below is a snapshot of FAO-56–based values for some familiar crops. These serve as reliable starting points:
| Crop | Initial Stage (Kc_ini) | Mid-Season (Kc_mid) | Late Season (Kc_end) |
|---|---|---|---|
| Tomatoes | ~0.4 | ~0.9 | ~0.75 |
| Sweet Corn | ~0.2–0.4 | ~1.1 | ~1.0 |
| (Other guidelines available for peppers, beans, etc.) |
For example, for tomatoes:
Kc_ini ≈ 0.4
Kc_mid ≈ 0.9
Kc_end ≈ 0.75
These values align with typical findings in agricultural guidelines.
From Kc Tables to a Watering Plan: Here’s How the App Helps
1. Choose Your Crop & Soil Type
Irrigation Calculator Pro lets you select a crop (e.g., tomato or corn) and automatically applies the correct Kc for that stage.
2. Enter ET₀ and Recent Rainfall
Add your daily reference evapotranspiration and subtract any rainfall to account for natural moisture.
3. Calculate ETc Instantly
Using ETc = Kc × ET₀, the app computes your crop’s daily water needs accurately.
4. Get Clear Watering Guidance
The app displays:
Total volume required per irrigation
Suggested intervals based on soil water capacity
Visual schedule, history tracking, and CSV export for reporting
All with just a tap, and fully offline.
Why This Approach Works
Science with zero extra coding: FAO‑56 logic, preloaded and simplified.
Stage-specific accuracy: It matches water to crop growth stage without manual lookup.
Quick results: Saves time and removes calculation errors.
Privacy assured: No internet or tracking required; all data stays on your device.
Practical Example
You’re growing sweet corn:
Select Sweet Corn, mid-season stage (Kc_mid = 1.1).
Input ET₀ (e.g., 6 mm/day) and rainfall (e.g., 2 mm).
Let the app compute ETc and give you precise volumes and the next irrigation date, effortless and data-driven.
Final Thoughts
Understanding Kc doesn’t have to be complicated. With Irrigation Calculator Pro, you skip the tables, the math, and guesswork, getting accurate, stage-aware irrigation schedules in seconds.
References
Determination of Crop Coefficients and Water Requirement of Tomato at Werer, Middle Awash Valley of EthiopiaCeresAI: Getting started with crop coefficients for orchard irrigationAsk IFAS: Evapotranspiration-Based Irrigation for Agriculture: Crop Coefficients of Some Commercial Crops in FloridaFAO: Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56Joseph C. Henggeler: Procedure to easily Fine-Tune Crop Coefficients for Irrigation SchedulingFAO: Chapter 6 - ETc - Single crop coefficient (Kc)