Final answer:
To find the number of days between irrigations for a corn field with a 5-foot root zone, calculate the available water, adjust for maximum allowable depletion and irrigation efficiency, and then divide the depletion threshold by the adjusted daily evapotranspiration.
Step-by-step explanation:
The question asks how many days between irrigations are needed for a field of corn with a specific set of parameters. To calculate this, we should first determine the total available water holding capacity (AWHC) for the root zone, which is the product of the AWHC per foot and the depth of the root zone. In this case, AWHC is 1.5 inches per foot for a 5-foot root zone, which gives us 7.5 inches of water available for the corn.
Next, we'll calculate the maximum allowable depletion (MAD), which is 58% of AWHC. Thus, 0.58 x 7.5 inches = 4.35 inches is the amount of water that can be depleted before irrigation is required.
The crop evapotranspiration (ETc) is 0.40 inches per day, and we need to adjust it for irrigation efficiency (IE), which is 77%. The adjusted ETc is then ETc / IE. We divide 4.35 inches by the adjusted ETc to determine the number of days between irrigations.