20.8. Crop Coefficients and Reference ET (ET₀)

Try these first

1. 1.

   What does ET₀ represent?

   Hint

   Think of the ideal conditions for well-watered grass.

2. 2.

   What is a crop coefficient?

   Hint

   Remember how different crops require different water amounts.

3. 3.

   What does the crop coefficient (Kₐ) represent?

   • The evapotranspiration rate from a reference crop
   • A factor that adjusts ET₀ for specific crops
   • An average temperature value

   Hint

   Think about how each crop has its own water needs.

4. 4.

   True or False: ET₀ is only relevant for irrigated crops.

   • True
   • False

   Hint

   Consider the broader applications of ET₀ in agriculture.

5. 5.

   Given a reference ET₀ of 7 mm/day, calculate the total water need for a field of tomatoes with an average Kₐ of 0.8 over 30 days. What would be the total water application?

   Hint

   You need to multiply the Kₐ, the daily ET₀ rate, and the number of days.

6. 6.

   A mixed crop farm has 50% maize, 30% soybeans, and 20% wheat. The respective Kₐ values for these crops are 1.2, 0.7, and 0.9. What would the weighted average Kₐ be for irrigation calculations?

   Hint

   Combine each Kₐ value multiplied by its respective fraction of the total crop area.