When Palle Pedersen came to Iowa State University seven years ago, his mission as the new ISU Extension soybean agronomist was to boost Iowa soybean yields. Farmers believed soybeans had reached a yield plateau. Corn was gaining much more yield per acre each year and making more money. For many, a bean yield in the 40-bushel range was all they were getting as a whole-farm average.
The ethanol boom was beginning, and demand for corn to make the farm-grown fuel was ready to rocket upward. Instead of rotating corn with beans, more farmers were planting a greater percentage of their acreage to corn on corn. Soybeans needed a boost.
While 40-bushel beans were the concern seven years ago, farmers complain about 50-bushel beans today. However, that’s a big improvement in yield in a short time period. Farmers have found they can produce higher bean yields, thanks to better seed genetics, improved technologies and sharpening their production practices.
Pedersen recently resigned his ISU position to take a job with Syngenta, and Jan. 31 is his last day at ISU. Looking back at the seven years, “we’ve learned there are some key things farmers can’t ignore if they want to maximize bean yield,” he says.
• With improved genetics now becoming available, bean yield potential is rising.
• But it still takes careful management to boost your farm’s bean yield average.
• Combination of management and variety selection is solution to maximize yield.
What’s holding beans back?
Through the checkoff and the Iowa Soybean Association, Pedersen has conducted several large projects since 2003 to find what it takes to raise high-yielding beans. What has been the most interesting part to work on?
“The importance of early vegetative growth,” he says. “The main problem soybeans run into is farmers manage their corn first, then focus on beans as time allows. As long as that’s the case, many will plant beans too late.”
Previously, “we never paid much attention to what’s happening prior to flowering. That’s a mistake,” he says. “I don’t believe there are any farmers in Iowa who haven’t heard me talk about the importance of planting date. And there’s a reason. Soybean planting date is our ‘soybean yield stimulus package.’ By planting early we stimulate the plant to achieve higher yield potential.”
Unfortunately, “we aren’t doing a good enough job,” he says. “Our data shows we need to be done planting soybeans anywhere in Iowa by May 15, but based on USDA planting progress data over the last five years, we often only have 50% of our acres planted by that date.”
Pedersen adds, “One of the major reasons why early planting is so important is we want to be sure the plant intercepts as much solar radiation [sunlight] as possible. There’s a close relationship between seasonal canopy photosynthesis and yield. So, by shorting our growing season by planting a variety that’s too short or planting too late, we reduce yield. That’s also why I don’t recommend planting in 30-inch rows: Canopy closure takes too long if there is some kind of stress.”
Planting early gets you an early start to capture as much light prior to flowering as possible. It helps you build the foundation for a fast-growing plant that will have less aborted flowers. Any sunlight hitting the ground is wasted and will not contribute to yield.
“Early-season stresses are extremely detrimental to soybean yields,” he says. “Weed competition is probably our biggest headache, and that’s why I’m a big believer in using a preemergence soybean herbicide in addition to glyphosate post, to reduce the risk of early-season weed competition. Weeds compete directly with beans for nutrients, moisture and light, thus reducing yield.”
5 very important steps
Pedersen cites five steps you can take to maximize yield:
1 “Variety selection is the most important management decision a farmer has to make every year,” says Pedersen. “We can do everything right [planting date, row spacing, weed management etc.], yet we lose our entire yield potential if we aren’t careful when selecting varieties.”
2 Soybean cyst nematode continues to be a big yield robber in many fields. SCN’s effect is more noticeable in dry years than wet years, but it is there. One key that has changed is more and more varieties are now available with SCN resistance. “With the improved yield stability of SCN-resistant varieties, you can choose a high-yielding SCN-resistant variety today,” he says.
3 Disease resistance is a third factor when choosing varieties. Know the disease history of fields, which diseases are most important, and select soybean varieties accordingly. Yield reduction from the common diseases is manageable. But certain diseases may be more of a problem because of field location, soil type and drainage.
“We are usually not confronted by one disease, but a complex involving several plant pathogens,” says Pedersen. “Using resistant varieties is a cheap, practical control for bean diseases in Iowa. Problem is there are no soybean varieties resistant to all diseases. The majority of farmers in Iowa need either sudden-death syndrome resistance or brown-stem rot resistance in addition to SCN. Both diseases can be managed well with variety selection.”
White mold, however, is more of an agronomic and cultural issue, with little tolerance found in the current varieties.
4 Plant early and in narrow rows. Early planting of beans is the cheapest, most efficient way to boost yield. Pedersen conducted many trials across Iowa with different varieties, different tillage systems and at more than two dozen different locations. His conclusion is the optimum time to plant soybeans is the last week of April for the southern two thirds of Iowa and first week of May for the northern third of the state, if soil conditions are suitable.
Since 2003 Pedersen and his students have done extensive research comparing wide rows (30 inch) to narrow rows (15 inch). “On average, we’ve seen a 4.5 bushel-per-acre yield advantage with 15-inch vs. 30-inch row spacing,” he says. “Narrow rows have a yield advantage because they achieve canopy closure more quickly, particularly in a stressful year, and intercept more light throughout the growing season.”
5 Weed management is now the biggest threat to profitability, he says. “Most growers are applying glyphosate-based herbicides too late for effective early-season weed control, which reduces yield. Another problem is the presence of glyphosate-resistant weeds, recently confirmed in Iowa.”
He thinks farmers understand soybean production better now, and they question what it takes to raise higher yields. They’re also planting better genetics with better disease resistance today, and more are using fungicide/insecticide seed treatments that allow them to protect against insects and diseases when planting early.
Bean yields the last two years disappointed many farmers. Iowa had 46 bushels per acre for a state average in 2008. But when you think about the flood of 2008 and all the related problems, that 46-bushel yield average may not have been too bad. In 2009 the state averaged 51.5 bushels per acre. “It was 4 or 5 degrees warmer on average in Denmark than it was in Iowa this past summer,” says Pedersen. “Iowa’s cool 2009 summer made a big difference; warmer weather would have added a lot of yield since we know seasonal photosynthesis is so important to maximize yield.”