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Orchard Irrigation:  Case Study

 

Following is an example of how to calculate water needs for a mature peach orchard just prior to fruit harvest.  The orchard is on a deep sandy loam soil with row middles planted to grass cover. 

Water use (Expenses)

  • ETr values are 2.10 inches per week (weather station data). 

  • Crop coefficient is 0.98 (Growth stage = 130, from Figure 10.3).

  • ETcrop  = ETr × Kcrop

  • ETcrop  = 2.10 inches/week × 0.98 = 2.06 inches/week

Soil storage capacity (potential bank balance)

  • The total storage capacity for readily available water over the 2 foot effective rooting depth is 1.5 inches.
  • 1.5 inches ÷ 2.06 inches per week = 0.73 weeks or 5.1 days between irrigations.

Restated, soil moisture in the root zone will go from capacity to plant stress levels in 5.1 days.
To recharge the soil profile, you will need to add 1.5 inches of water.  Assuming a microsprinkler irrigation system with an efficiency of 80%, 1.9 acre inches of water application will be required per acre for each watering.

Good irrigation management requires:

  1. An understanding of the soil-plant-water relationship.
  2. A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system.
  3. Proper timing based on oil water holding capacity, weather and its effects on crop demand, and stage of crop growth.

Each of these components requires a commitment to proper management.  Proper irrigation management will provide the most efficient use of water, and will optimize orchard yields in balance with long term orchard health and  productivity.