- Determining Your Crop Coefficient (Kc) with turfRad Predict

At some point, once you’re using turfRad regularly, a different question comes up: How much water is my turf actually using? 

Because irrigation decisions don’t just depend on what the moisture was this morning, or is this evening, they depend on how fast that moisture is going to change tomorrow. This is where the Predict feature becomes useful. 

And more specifically, where you can start dialing in your effective crop coefficient (Kc) based on how your turf and soil is actually responding to the weather, not just calculated estimates. 

Why Crop Coefficientc Kc Matters in Daily Irrigation Decisions 

Crop coefficient (Kc) is what connects: 

• Weather  

• Reference Evapotranspiration (ET₀)  

• Actual moisture loss in your soil (often called ET_a [actual] or ET_c [crop])  

Most systems (and users) use generalized Kc values. For example 0.6 is a common general value for warm season grasses, and 0.8 for cool season.  

But every course is different. 

• Different grasses  
• Different rootzones  
• Different management styles
• Different micro-climates  

Which means: Your actual water use is almost never “average.” turfRad allows you to tune this using real moisture data from your course. 

Start With the Right Conditions 

Before adjusting anything, you need clean data. The goal is to isolate natural moisture loss due to evapotranspiration, without irrigation interfering. 

Look for one of the following: 

• Two consecutive days where you scanned both days  

• No irrigation between those scans  

Optional (but important): 

• If there was precipitation, make sure the forecasted precipitation matches your on-site weather station  

If rainfall data is off, your Kc adjustment will be off too. 

Use Predict to Match Measured vs. Expected 

Once you’ve identified the right timeframe, go into Predict mode. You can access this in two ways: 

• Through the Dashboard  

• By selecting a fairway or sprinkler in the overview  

See where to navigate to predict mode: dashboard overview here 

Now you’re comparing two things: 

• Measured moisture change (what actually happened)  

• Predicted moisture change (what the model expects)  

Your goal is simple: Make those two lines match. 

Adjust the Crop Coefficient (Kc) 

Inside Predict, adjust the Kc value until: 

• The predicted curve aligns with the measured data  

• The rate of moisture decline matches what you observed between scans  

You’re not trying to force a perfect fit. You’re trying to get a realistic representation of how your turf uses water. Once those lines align, you’ve effectively tuned your Kc to your course conditions. 

What This Means in Practice 

Once Kc is dialed in, Predict becomes much more powerful. 

You can now: 

• Anticipate how quickly areas will dry  

• Plan irrigation timing more accurately  

• Avoid over- or under-watering based on generic assumptions  

And most importantly: Your predicted moisture is now based on how your turf actually behaves, not how it’s supposed to behave. 

How the Kc Impacts your Moisture Predict 

By tuning your Kc value either on the global (full course) data or over a representative fairway, we are adjusting for the reality of how your course loses water compared to how the weather model forecast predicts moisture loss.  

We are able to generate one reference evapotranspiration (ET0) value for your whole golf course so we also use one Kc value to represent the overall course. In reality there may be some spatial variation to Kc, but getting the setting right on the course level will greatly improve the accuracy of the prediction model.

Key Takeaway 

Kc isn’t just a number. It’s a way of understanding how your turf system responds to weather. turfRad gives you a way to measure that directly, by comparing what should happen with what actually happens. 

And once those two align, your irrigation decisions become predictive, not reactive.