As with most legumes, soybeans dislike having their feet wet for very long. But some soybean strains tolerate waterlogging much better than others.
Finding and propagating these “web-footed” varieties is the quest of plant breeders in Missouri and Arkansas.
“There's a wide difference in how well soybeans tolerate flooding,” says Grover Shannon, soybean breeder at the University of Missouri (MU) Delta Center. “Half of the farmers in this region irrigate soybeans. If a farmer puts on an irrigation flood, then gets a big rain, he can lose his crop — or at least suffer a lot of damage. We want to identify those soybeans that best tolerate waterlogging.”
Shannon and Pengyin Chen, his counterpart at the University of Arkansas, have screened hundreds of varieties over the past three years to identify and select those that are most tolerant to flooding.
For most soybean producers, the problem may be too little rather than too much moisture during the growing season. Still, in a typical year across the U.S., excess soil moisture affects one out of eight crop acres.
“Yield losses due to excess soil moisture are common in the Midsouth, due to the prevalence of heavy clay soils, poor surface drainage, high rainfall amounts and cropping practices,” says Chen. “For example, soybeans are the rotation crop of choice for most rice growers in fields that are ideal for rice production but less than ideal for soybeans. If waterlogging occurs during the reproductive stage, soybean yields may be reduced by 50% or more.”
Funded by the Missouri Soybean Merchandising Council, Shannon has evaluated the 400 or so soybean lines in the Missouri variety trials, plus germplasm from China and Japan. Chen has done similar screening in Arkansas.
The screening technique is pretty straightforward: Soybean varieties are planted in zero-grade (perfectly flat) plots with levees erected to contain the flood. At about early bloom stage, plots were flooded with water to a depth of 4-5". The flood was left until evaporation and soil saturation got rid of the excess water. Some lines tolerated flooding very well; some were dead by the time the water went down. At harvesttime, Shannon and Chen measured the yields of the survivors.
“Our first goal was to identify those varieties that are most flood-tolerant and get the word out to growers,” says Shannon. “We've done that. Now we're making crosses of the more flood-tolerant varieties to develop genotypes that can be used as parental lines in private and public soybean breeding programs.”
Chen says for this stage they are doing genetic studies of selected lines that they hope will let them identify the gene or genes controlling flood tolerance.
“We're trying to give soybean growers a little time — a little insurance against flood damage,” says Shannon. “Producers can tell you which varieties will or will not take excess water. In fact, I got interested in this project after talking with farmers.”
Ideally, Shannon and Chen hope their work will result in soybean varieties that are flood-tolerant, disease-resistant and Roundup Ready — and with good yield potential.
“Low-tech, high-tech, biotech — growers will not plant a variety that doesn't yield well, regardless of whatever other traits the variety may possess,” Shannon adds.