AMES, Iowa – With memories of the last fall’s difficult harvest still all too vivid for farmers, this winter has presented its own challenges. And now, according to an Iowa meteorologist, a wet spring is predicted.
“Soil moisture levels are at or above field capacity. It will not take abnormally high amounts of April precipitation to leave large portions of the Corn Belt too wet for effective planting,” says Elwynn Taylor, Iowa State University (ISU) ag meteorologist. “The El Niño weather of February brought substantial moisture in a band across the southern United States. As the weather patterns migrate north in the spring, a wet planting season is a threat.”
One of challenges facing farmers will be compaction.
“Farmers did what they had to do to get crops out last fall, but there will be ramifications,” says Iowa Soybean Association Director of Production Research David Wright. “Heavy wagons, trucks, grain carts and combines moving across wet ground all contributed to soil compaction. There are now some things farmers need to watch for in the 2010 soybean crop.”
The heavy snow accumulation is going to cause further complications this spring. If the water from melting snow isn’t able to percolate down through the soil, fields will be wet, even without excessive additional rainfall. This will put additional pressure on Iowa’s farmers to delay spring tillage to keep from further compacting the soil.
“Spring is not the time to alleviate compaction, but farmers will want to avoid creating more compaction,” says Greg Brenneman, ISU Extension ag engineering specialist . “With wetter soil, that is more of a challenge. I would advise farmers to not try to get out in the field very early. Doing so and working wet soil will create more compaction.”
In particular, farmers who didn’t get to do as much field work as they would have liked last fall may feel like their window of opportunity is short. It will be a challenge to let fields dry out.
“Soil has a natural way, through thawing and freezing, to remedy soil compaction and improve soil structure,” says Mahdi Al-Kaisi, ISU Extension agronomist. “Stable soil structure is like a building block formation that is able to hold up the weight of implements running over them, while still forming conduits for water to move through and providing natural aeration for a root to grow. Because of the stable and strong soil structure, untilled soil can tolerate the weight of machinery. Tillage breaks up that soil structure, reducing the soil’s strength to hold the weight of heavy equipment.”
While farmers think tillage will reduce soil compaction, Al-Kaisi says it will actually only make it worse. It won’t cure the deep soil compaction and, by disturbing the upper soil layer, will destroy soil’s natural structure or soil aggregates and creates another layer of compaction under heavy rain and field traffic.
“Put simply, the more wheels and machinery that move over wet soil, the more compaction will take place,” John Holmes, ISU Extension field agronomist, says. “Avoid making any more trips than absolutely necessary across a field with wet soil.
“This may be a year for farmers who work their soil to try doing less tillage than they normally would,” Holmes says. “For instance, if they didn’t get chiseling done last fall, they may forego it this spring and just do the secondary tillage just before planting to prepare the seedbed. Though it might be a challenging year to try something new, they may decide to try some no-till, especially in soybeans, where they didn’t get fall tillage done or in fields where corn didn’t get combined until spring.”
Holmes adds, “In parts of the state where farmers feel they must do something, this is a year when an implement called a rotary harrow might be useful, though in most of the state, these are not common.” Not the same as a rotary hoe, the rotary harrow has single lines of heavy teeth that poke holes in the ground without stirring it up and allows water to penetrate. It can dry out the ground and yet isn’t aggressive.
Though researchers have documented the yield benefits of early planting, agronomists emphasize it is more important the soil is ready. A few days can make a tremendous difference in the soil’s condition.
“Being patient will pay off,” Al-Kaisi says. “Farmers need to know their own soil and their fields.”
Planted in wet fields, young soybean seedlings could have problems with root development, which may, in turn lead to further problems.
“I’d encourage farmers to plant seed with excellent resistance to diseases,” Holmes says. “Since the seed will likely be going in a cold, damp soil, it would be a good idea to treat it with a fungicide.”
“There is no question that seed treatments can increase yield in fields where risk of seedling diseases are high,” says ISU Plant Pathologist X.B. Yang. “Seed treatment will not improve germination rate, but will protect against further stand loss if fields have a history of damping off and the spring is wet. If the planting season is going to be cool and wet, the value of using treated seeds increases.”
“Wet, saturated soil conditions at planting can increase the risk of damping-off caused by Pythium and Phytophthora,” says ISU Plant Pathologist Alison Robertson. “These pathogens cause similar symptoms on soybean seedlings, and lab tests are usually required to distinguish which pathogen is present. Pythium prefers cooler, saturated soils and is more of a problem in early planted beans. Phytophthora may be an issue when the soil is warmer and saturated.”
According to Robertson, soybean varieties with resistance to Phytophthora pathogen are available, but varieties with resistance to Pythium are not available. “Seed treatments can reduce risk of early season damping off from both diseases. Growers should consider a seed treatment if particular fields have a history of damping off,” Robertson says.
“As the season progresses, there may be further effects from the winter that will pose problems later in the summer,” Wright says. “For instance, we don’t yet know the impact of all the snow cover on the overwintering of the bean leaf beetle or aphids. Soybeans planted in compacted fields that have experienced problems with root development may be susceptible to problems with foliar diseases like sudden death syndrome (SDS). While SDS infection occurs shortly after germination, symptoms may not be apparent until later in the summer. Additionally, if the young seedling roots have difficulty taking up enough potassium, those soybeans could be more attractive to soybean aphids later in the summer. There may also be issues of delayed maturity.”
Time will tell on some of those issues. For now, Holmes sums up what farmers can do: “Be aware that compacted soil is wet soil. Try not to make the compaction worse. Wait until the soil is drier. Plant seed with excellent resistance to diseases. Since it will be going into cold, damp soil, treat seed with a fungicide and avoid making any more trips than absolutely necessary across a field with wet soil.”