University of Nebraska-Lincoln scientists are developing a new approach that delays soybean irrigation until early-pod formation in July, relying on stored soil moisture and early-season rainfalls while still helping produce high yields.
They've tested the approach on university plots the last two growing seasons and plan to further test it on a half dozen or so Nebraska farmers' fields this year. "We've learned a lot about how to irrigate soybeans that is quite remarkable compared to how most farmers now irrigate," says Ken Cassman, UNL agronomist.
The project builds on years of research by Cassman's colleague, soybean geneticist Jim Specht, into soybeans' drought resistance and the best methods of irrigation.
Typically, producers plant soybeans in early May and begin irrigating in June. In years with average or above-average early-season rainfall, that can result in too much water being applied to plants. In turn, that can result in taller and leafier soybean plants that can lodge later and are more susceptible to disease.
Avoiding too much early irrigation, on the other hand, encourages soybean plants to develop stronger, healthier root systems that grow deeper in search of moisture.
"You defer irrigation because there's typically enough stored moisture and enough rainfall even in dry years to create a soybean plant that can achieve high yields," Specht says.
On average, soybeans grown with deferred irrigation on university plots in 2006 yielded about 83 bushels an acre, slightly more than the 78 bushels yielded under a season-long irrigation approach. Similar results were seen in 2007.
Specht says those results are particularly impressive given the drought conditions that prevailed on East Campus plots in June and July. "We were hoping Mother Nature would challenge us, and she did," he adds.
Soybeans need about 19 inches of water from planting in early May to harvest to yield about 85 bushels. If they don't get any of that from early-season rains, producers will have to catch up with irrigation once deferred irrigation begins in early July. But if early-season rains are normal, the deferred approach could reduce the amount of irrigation water applied throughout the season.
"So many producers have asked me 'when should I water my soybeans?'" says Richard Swartz of Minden, a producer and member of the Nebraska Soybean Board. "This study should answer some of those questions."