Art and Science of Soybean Maturity Ratings
Hot and dry, cold and wet, early spring, late spring, early frost, late frost … erratic weather has become the new norm. While full service ag retail, custom applicators and farmer customers bounce around scheduling like a pinball game, one of the few constants is recommended soybean maturities. The photo period-sensitive soybean is uniquely suited to flex with the weather, thanks to long refined and continually reevaluated maturity ratings. Add in the indeterminate nature of most varieties from group four and earlier maturities, and flexibility increases.
“Every soybean research station is georeferenced to where the soybeans will be planted and varieties evaluated for soil types and weather patterns in the area,” said Doug Tigges, genetics product manager, Syngenta Seeds. “Most new products are wide area tested for two years before launch. Putting a relative maturity rating on them is still a combination of art and science. We start with an estimated maturity rating based on parent lines, but it is finalized over the two years as it is compared to internal benchmarks such as a recognized standard variety.”
Tigges explained that in its first cross, a new variety population might have a half to a full maturity group range with a wide variety of plant heights. As the most desirable plant features are selected for, the maturity range narrows. It is that evaluation that involves the art. Although technology such as remote sensing and imaging may be used, it is the on-the-ground evaluation that is the final determinate. It is one reason that a Syngenta group 2.3 might not get the same exact rating from a competitive company. It is also why a group rating can change over time.
“We may say it is a relative maturity 4.1, but some years the product development team may say it looks more like a 4.3 or a 4.0,” said Tigges. “We may see a little variation over time; however, most growers likely won’t see a difference.”
RATINGS CHANGING AS PRODUCTION MOVES
A symbiotic expansion of planting and research by growers and companies is pushing soybeans farther west and farther north every year. Group zero soybeans have been supplanted by group double zero, and now triple zero, as soybeans make their way through North Dakota and into Montana and Manitoba.
“As we get into ever earlier varieties, it is even more important to have research located in the target geography,” said Steve Schnebly, senior research manager, soybeans, DuPont Pioneer. “We used to do a lot of group 00 and earlier product development research in North Dakota, and yet when those varieties went into Manitoba, they didn’t look as good.”
DuPont Pioneer, Syngenta and others are now doing research on suitable maturity corn and soybeans at company research stations in Manitoba. At one time, DuPont Pioneer’s station was largely dedicated to canola research, but it is now fully multi-crop.
“Our research into double zero and triple zero is much more eff ective there than it was before,” said Schnebly.
Moving west has its own complications with maturities. Although the group rating is largely determined by when the photo period triggers reproduction, it is also influenced by climate. A generally warming climate is expanding expected frost-free days. This has affected the move north, but may also impact other areas to a lesser degree.
“We may see a slight change in ‘fuller’ season maturity recommendations in many areas,” said Tigges. “Regardless of when you plant, the typical soybeans will mature at around the same time. However in northern growing areas, if you used to risk frost the first half of September and now it is the first of October, that allows you to plant a longer season variety or consider planting soybeans as a cash crop where you never did before.”
In the increasing elevations of the West, frost-free days and associated factors come into play. “As we increase in elevation, we go to a shorter season variety, but we are also going to a drier environment,” said Schnebly. “As breeders look ahead, they talk about diversity in germplasm. The question is how fast can we integrate germplasm in a variety while maintaining maturity.”
Expanding geography for planting soybeans and fluctuating weather complicates selection of soybean seed with the right maturity rating.
MOVING RESISTANCE TRAITS
The diversity question comes into play in more traditional maturity zones as well. Even though higher temperatures with climate change won’t influence maturities, it is having an influence on disease. As a result, breeders are working to move resistance to traditionally more southern diseases and pests from determinate, long-season, group five and six varieties north to indeterminate, group 4 and earlier varieties.
In many cases, that is easier than selecting for maturities, thanks to advances in trait marker technology. While markers can verify that soybean cyst nematodes, sudden death syndrome or iron chlorosis traits are present in the new variety, only time spent in a given location identifies the maturity.
“Developing a new variety is a combination of markers and local evaluations,” suggested Schnebly. “Marker technology and the use of tropical nurseries has shortened the variety development program to seven to eight years versus 10 to 15 in the past. Although we’ve made significant progress in identifying genes that affect maturity and other aspects of the soybean crop, the soybean industry is still in the early phase of finding markers for maturity.”
Tigges suggested that in some ways growers might still be in the discovery stage with soybeans. He noted that many will spend hours on corn hybrid selection to get a 5 percent yield advantage, yet spend minutes on soybean variety selection, bypassing opportunities for similar increases. Part of that he attributed simply to quantity. A 10-bushel increase in 200-bushel corn seems significant versus a 2-bushel increase in 50-bushel soybeans.
“The tendency is to credit the hybrid for the 10-bushel increase, but assign the soybean increase to diff erences in soil, weather or other factors,” said Tigges. “One of the messages to growers is that if you manage your soybean crop more intensively, you will produce more yield.”
Selecting which maturity or maturities to go with, like pest resistance and weed control, are all factors Tigges suggested spending more time on. Maturity selection is especially important for growers trying to manage workload at harvest.
“They may want to plant several maturities to spread out harvest, with earlier maturities to start with and then move to mid and full maturities for maximum yield potential,” he said.
MAXIMIZING MATURITY WITH WEATHER
The later the maturity, the greater the potential the soybeans will capture the benefit of mid- to late-August rains, as many fields did in the otherwise hot and dry 2012. Even in 2013, with planting in many areas extending into late June and early July, full-season varieties had time to mature.
“With soybeans, you have to think about when do you normally not get rain and will you get through that period with your variety selection,” said Tigges. “From a risk management perspective, you may want some early season soybeans in case the weather is the opposite with early or midsummer rains, but generally the later you get into August, the more likely you are to get a beneficial rain.”
Schnebly pointed out that early varieties in 2012 tended to be done pod filling when the late August rains came. Even without that, the yield advantage of full-maturity varieties for a given area are clear, he added. “For each day of maturity, you gain up to half a bushel of yield,” said Schnebly. “Selecting a 2.0 versus a 2.3 can add a bushel and a half. Pushing maturities to the max can push the reproductive period to maximum yield in a good year. Some will push it to the edge, but all it takes is an early frost to bring them back into the fold.”
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