Why do we irrigate soybeans? If your answer is to increase plant size, then full watering throughout the growing season is a good idea. But if your answer is to improve yields and increase your bottom line, then how you water soybeans requires a little more management.

WHEN TO WATER: At a field day near Orchard recently, Chuck Burr, UNL Extension water and cropping specialist, told producers that holding off on full irrigation until R3 appears to boost yields.

There is a price to overwatering soybeans, said Chuck Burr, University of Nebraska Extension water and cropping specialist. At a recent Soybean Management Field Days presentation near Orchard, Burr said that excessive watering on soybeans increases production costs, can cause erosion and environmental degradation, and doesn’t necessarily translate into increased yields. “There are additional fuel costs to watering during the vegetative growth period,” Burr said. “There could also be extra harvest losses with soybean plants that are too tall because of overwatering. Soybeans can be stressed during the vegetative growth period with minimal to no impact on grain yield,” Burr said. “Just don’t stress them when they are filling pods.”

He backed up the recommendations with UNL irrigation studies on soybeans. Research conducted at four Nebraska locations showed that on silt loam soils with a full soil water profile at planting, delaying irrigation until R1 or R3, at flowering or the beginning of pod elongation, provided equal or better yields than when irrigation treatments were begun during the vegetative stages.

Burr told producers that for 2015’s irrigation trials, there was very little additional soybean yield from irrigation treatments that were considered full irrigation or limited at 75% of full irrigation, compared to the rain-fed trials. The only treatment that had a positive impact on yield was the 50% irrigation treatment early in the growing season and full irrigation late in the season. This treatment had the highest water use efficiency, adding an extra 1.8 bushels per inch of irrigation water.

“On soybeans, it is best to monitor soil water status and to dry the profile down somewhat during the vegetative growth stages, so you have room for rain,” Burr said. “Delay watering early, and watering later in the season gave us the best yields.”

There are several irrigation management apps and online simulation models available through UNL to help manage soybean irrigation, including CornSoyWater and CropWater.

Visit cropwatch.unl.edu for more information. You can also get more details by contacting Burr at [email protected].