Calculating the irrigation schedule, based upon the actual field information, is where sustainable water savings occur. In calculating the irrigation schedule the following factors are used to create the most efficient irrigation schedule possible:
Evapotranspiration
Evapotranspiration is the amount of water used by a landscape. Evapotranspiration is the water loss in the landscape due to evaporation and the water used by plants in transpiration. Evapotranspiration varies by geographic location, seasonal weather patterns, plant material, local site conditions, and soil type.
Soil
The type of soil effects the amount of water that can be stored in the soil. Sandy soils will hold less water than clay soils. The infiltration or percolation rate will vary by soil type. The infiltration or percolation rate is how fast a soil type can absorb water. This will vary based upon soil texture, structure, degree of compaction, and slope.
Plant Materials
Different plants have different water use requirements and different rooting depths. The size, age, and location of the plants all effect water usage. Location, exposure, and the active root zone depth all effect plant water usage and must be considered when creating the base irrigation schedules.
Sprinklers
The information from an audit is used to determine how long each system needs to operate to apply the correct amount of water. The more efficient the irrigation system the less time the system needs to apply water. Lower precipitation rates will result in longer run times and potentially less water runoff.
Schedule
An irrigation schedule is then developed for irrigation system. The water requirement is adjusted based upon the efficiency of the irrigation system as determined by the field test information. The soil type is used to determine how much water to apply. The soil and root depth determine how long to run. The amount of time between irrigation cycles is also determined by the soil type and rooting depth. Allowing the water to soak into the soil to the proper root zone depth without saturating the soil for long periods of time is an important feature of an irrigation audit. Most irrigation systems will never reach this level of efficiency without an irrigation audit.
The objective of a great irrigation schedule is to apply the correct amount of water necessary for the optimal growth of the plants in the field. When properly developed, this prevents over and under watering the field. When the irrigation schedule is not properly developed, shallow rooting occurs with short frequent irrigation cycles or run off occurs when water is applied faster than the soil can absorb the water.
Finally, after the schedule is developed, the irrigation zone run times are adjusted for seasonality. Additional adjustments are made throughout the season based on visual inspection to compensate for local factors.
Irrigation audits are an essential part of any water conservation program. An irrigation audit is a very sophisticated process used to create an optimized irrigation schedule. Most irrigation systems apply more water than needed to maintain a healthy field.
