Soggy and cool conditions have kept farmers out of the field, and the optimal planting dates for soybeans, April 25 in southern Iowa and May 1 for the northern half of the state, have come and gone. The average rainfall in the state of Iowa for April 2011 was 5 inches, or about 1.36 inches above normal. In April 2008, the second wettest April ever recorded in Iowa, the precipitation totaled 5.88 inches, or 2.55 inches above normal.
In addition to rain concerns, Iowa State University Extension climatologist Elwynn Taylor says the strong shifts between cool and warm weather will likely continue through the rest of this spring and into summer, since La Niña is the strongest it has been in 50 years.
"The National Weather Service forecasts the rest of spring to be on the cool side of average," Taylor says. "We expect equal shifts from one extreme to the next every couple of weeks, which is not favorable for crops. Yields this year are expected to be below normal due to La Niña conditions. However, we need to keep an eye on La Nina. If it fades away before June, weather prospects and crop yield potential in the U.S. Corn Belt would improve considerably."
Potential yield loss increases for beans planted after May 10
David Wright, director of contract research for the Iowa Soybean Association, says it's unlikely farmers will get soybeans planted early enough to maximize the growing season. Farmers can expect to lose 0.3 to 0.7 bushels per acre per day due to delayed planting. Yield loss may be more in fields planted after May 10. However, Wright warns against rushing the process. Don't "mud in" your soybeans just to get them planted by a certain date.
"Even though planting has been delayed, don't rush and mud it in if our current rainfall pattern continues," Wright says. "The extra couple of days waited will have benefits later on in the growing season. The biggest risk in mudding-in is sidewall compaction, which limits soybean growth and root development."
Wright explains early root development is critical to provide healthy roots and rapid vegetative growth. "Soybeans need a healthy, vigorous root system to take up water and nutrients and for later in the season when rainfall may be less abundant," he says. "It's the number of roots that matters during the critical seed-fill period because water and nutrients are taken up into the root just behind the root tip. More root tips equals greater stress tolerance and yield potential."
Soil conditions at time of planting are a key to seedling health
Mark Licht, field agronomist for ISU in west central Iowa, agrees that a major factor is considering soil conditions at the time of planting. "Farmers must be patient by not rushing in to plant in wet soil conditions," Licht says. "Waiting for suitable soil moisture and warmer temperatures will result in faster, more uniform emergence. Warmer, dryer soils also reduce the risk of soil-borne pathogens that can infect the plant, such as Pythium."
While many farmers and climatologists are comparing this spring to the spring of 2008, Wright says more farmers are using seed-applied fungicides this time, which may help reduce root infection by soil-borne pathogens. However, seed applied fungicides will not reduce the negative impact of soil compaction in the seed zone.
"2011 will be a good test of performance of fungicide seed treatments," Wright says. Licht agrees, "This year a fungicide seed treatment may be one of the more profitable inputs you can spend money on for soybean production, due to the risk of soil-borne pathogens."
Make sure you are timely with post emergence herbicide application
Wright adds, "Good weed management will continue to be critical, especially in later planted fields. Farmers should get a good preemergent herbicide applied if they can." However, if you are unable to apply a preemergent herbicide and end up relying solely on post emergence herbicide, Wright says it's important to apply that post emergence product in a timely fashion to reduce weed competition.
"Weeds are constant competitors for the water and nutrients soybeans need for fast growth and development," he says. "Iowa is predicted to plant 9.4 million acres to soybeans in 2011, with the capacity to plant a million acres a day. Farmers should consider first the best soil conditions, wait a day or two to plant if you have to, to get your crop off to a good start. Patience will pay off."