Though it's relatively early in the growing season, Iowa soybean farmers have already experienced a wide range of extreme weather conditions in 2011. All of these weather factors have an impact on soybean growth and could affect the yield potential.
David Wright, the Iowa Soybean Association's director of contract research, notes that this year, "In central Iowa, farmers have had too much moisture. We've also experienced multiple weeks of cool soil and air temperatures, followed by unusually hot, windy conditions. These extremes make a difference in soybean plant growth and development."
The extended forecast for Iowa continues to be for above normal precipitation and above normal high temperatures, a combination that can put additional stress on soybean plants.
Drier conditions are preferable during vegetative growth stages
In areas of soggy soils, Wright says, soybean root development is slowed by lower levels of oxygen and higher levels of carbon dioxide. "This slower root development could reduce the number of root tips, which is a primary factor in a plant's ability to uptake essential elements," he explains. "Water and nutrients are taken up just behind the root tip so the more root hairs a plant has, the greater its ability to compensate for heat and reduced soil moisture."
If conditions aren't too extreme, Wright says, it is actually preferable to have somewhat dry conditions during vegetative growth stages. "Where it is drier, soybeans will develop a more complete root system which will enable the plant to take up more water and nutrients during its reproductive phase," he adds.
Greatest yield loss when stress occurs between podset and seedfill
Research conducted in the 1980s concluded that young soybean plants are fairly resilient to stress during vegetative stages of development. The greatest yield loss comes when stress occurs between R3 (beginning podset) and R5.5 (seedfill nearly complete) growth stages.
While there's little a farmer can do midseason to compensate for weather's effects, Wright notes that understanding what goes on underground can help with future management considerations. One of the most obvious is to note wet areas in your fields, areas that may need tiling. Less obvious would be the need for fungicide and insecticide seed treatments.
In addition, farmers might consider making the transition to narrow rows and/or no-till practices. Iowa State University has documented a 4.5 bushel advantage for soybeans grown in narrow rows compared to 30 inch rows. Narrow rows develop an earlier canopy, which can help keep the vegetative tissue cool during periods of high heat.
No-till can improve soil structure and provide better soil drainage
No-till practices can also improve drainage by building soil structure so water doesn't stand on compacted ground. No-till reduces fuel, labor and equipment costs, while improving soil and water quality.
Wright says, "Using soybean management practices that can help a crop withstand Iowa's increasingly extreme weather conditions can result in a more resilient soybean production system. It's not too early to be thinking of management considerations for future crops. Pay attention to what you are seeing in your fields this summer and learn from those lessons."