Step 1. Determine your reference evapotranspiration (ETo)

Before planning your crop and irrigation system, you will need to review historical evapotranspiration data.

Reminder: Look at the full date sets of growing periods, not just isolated dates.

When your crop is planted, you will use real time evapotranspiration data to make daily and weekly water schedules, but for planning, we use historical data.

In both cases, ETo information is readily available from government meteorological agencies. However, for more accurate data, you may use your own weather station or evaporation pan method. The weather station method uses the Penman-Monteith equation to calculate evapotranspiration based on weather readings. If you are interested in the latter, google “Class A Evaporation Pan”, and keep in mind that you then need to use a pan coefficient to reach ETo.

An example of government evapotranspiration data (source

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