Don’t get caught out by rapid increases in crop water use in spring-early summer

Rapid crop growth combined with increases in seasonal water demand (ET_o) can increase crop water use by more than 400% in a matter of weeks. Watch your crop and weather conditions and be prepared to increase irrigation amounts to match crop water needs.

• Crop growth can be very rapidly increasing canopy cover. This can drive big increases in water use. For example, a lettuce crop can grow from established seedlings (crop factor of 0.25) to full canopy (crop factor of 0.8-1.0) very quickly.

• Evapotranspiration increases during spring, and typically peaks around mid January.  Get 7 day ET_o forecasts from IrriSAT or from apps like The Yield.

Combine crop factors and ET_o to get estimates of crop water use (ET_c):

ET_c = crop factor x ET_o

Remember to take into account crop development (crop factors) to get crop water use (ET_c), otherwise you are not getting the whole picture. See this corn factsheet for an example.