44.2.3. Methods to Determine IR

Try these first

1. 1.

   What is Soil Moisture Deficit?

   Hint

   Think about how much water is required compared to what is available.

2. 2.

   What is the purpose of the Crop Coefficient?

   Hint

   Consider how crops vary in water usage.

3. 3.

   What is the Soil Moisture Deficit?

   • Difference between holding capacity and moisture present
   • Total water in the soil
   • Water lost to evaporation

   Hint

   Think about the relationship of soil moisture and its capacity.

4. 4.

   True or False: The Pan Evaporation Method uses actual crop data to estimate water needs.

   • True
   • False

   Hint

   What does the method actually measure?

5. 5.

   A farmer wants to irrigate a field. The CWR is 120 mm, effective rainfall is 25 mm, groundwater contribution is 10 mm, and initial soil water is 5 mm. Calculate the irrigation requirement.

   Hint

   Identify each contributing factor carefully.

6. 6.

   During a hot season, a crop shows a Kc of 1.2 and the reference ET₀ is 6 mm/day. Calculate the crop's ET.

   Hint

   What does this Kc value indicate during hot weather?