When Should You Stop Irrigating? - Part One

For irrigators, the last pivot pass of the season is just as important as the first.

“If you stop irrigating too soon and stress the crop before the it reaches maturity, yields will be negatively impacted,” said Tim Wilson, irrigation engineering manger at Lindsay Corporation. “On the other hand, watering longer than you really need to adds unnecessary expenses and reduces profits and can leave the field wetter than desired come harvest time.”

So, how do you know when to stop irrigating? Wilson recommends looking at the soil instead of a calendar.

“There’s no hard and fast date,” Wilson said. “To calculate when and how much water to apply in the final stages of growth, growers need to monitor soil moisture and determine the crop growth stage. The University of Nebraska has some great tips for end of season irrigation at Predicting the Last Irrigation of the Season. Keep in mind, though, that these tips apply to Nebraska and should be adjusted for other locations.”

Determining when crops have fully matured and no longer need to be irrigated depends on the crop, but experts say there are a few general rules of thumb to follow.

Corn - Take a cob off the stalk, break it in half and take a close look at the kernels. If the milk layer is a third to halfway down the kernel, about three inches of water is still needed. If there is already water in the root zone, then little or no irrigation may be required.

Soybeans – Sufficient water is needed to allow full bean development and pod fill. Studies have shown that yellow pods sprinkled with brown are the best clue of physiological maturity.

Alfalfa – To maintain active growth, irrigate until growth is stopped by a hard frost. If there is no frost, then irrigation can continue. In more arid areas, it is a good idea to have some water in the root zone going into winter.

Potatoes – Research shows irrigation can be used to reduce bruising during harvest. If the soil is dry, apply a final irrigation pass before harvest.

For growers who don’t want to rely exclusively on visual inspections of their fields and complex calculations, Wilson recommends FieldNET Advisor™ – a new tool that drastically simplifies irrigation management decisions.

“FieldNET Advisor is an innovative solution that provides growers with continuously updated, science-based irrigation recommendations that are customized for each field,” Wilson said. “It takes the hassle out of irrigation and helps growers make better informed decisions about when to irrigate and how much water to apply.”

In part two of our series about when to stop irrigating, we will explain in more detail how FieldNET Advisor generates science- and data-based information that let’s growers know when it’s both agronomical and economically optimal to stop irrigating.

And for more information about FieldNET Advisor, talk to your local Zimmatic dealer or visit