Scheduling Irrigation with Farmwest.com

Farmwest.com can now help farmers decide when to irrigate and how much water to give their crops. How does this work?

The water requirement of any crop is directly related to 'evapo-transpiration'. Evapotranspiration or 'ET' is the total amount of water that evaporates from the soil plus the water released through the plant - called transpiration. ET can be calculated from air temperatures (and other measurements) obtained from weather stations.

Farmwest.com obtains daily weather data and 5-day weather forecasts for 42 weather stations in BC. Farmwest has a calculator that converts temperature data from the weather stations to ET values. Unfortunately, calculations that neglect wind and sunshine may over- or under- estimate ET. However, over a period of a week or more, our ET calculations are very close to the actual values. ET values are updated daily on farmwest.com. Farmwest also calculates a value for water deficit by deducting rainfall from ET.

Although ET tells you how much water can be lost, how much water is lost depends on the type and size of crop. When a crop is small, most of the ET occurs as evaporation from the soil surface. As the foliage develops, transpiration from the plant increases while evaporation from the soil surface decreases. The difference between how much water is lost from a crop compared to how much can be lost (ET) is given by a number called 'crop coefficient'. These values and other information on irrigation can be found on farmwest.com.

T. J. Nyvall, BCMAFF, Abbotsford