Not all soil is created equal, so if your soybeans are turning yellow it might be time to start thinking about iron deficiency chlorosis.
Speaking at a recent field day near Carman, Marla Rieckman told producers that wet, poorly drained land is often the culprit.
“One of the main causes of iron deficiency chlorosis is actually the presence of high carbonate levels or high-pH alkaline soil,” said Rieckman, a landscape stewardship specialist with Manitoba Agriculture, Food and Rural Development. “These are soils that are typically poorly drained… carbonates in the soil move with water, but they move slowly with water, they don’t move as fast as salts do with water.”
The problem is that iron is not particularly soluble in alkaline soil — wet soil with carbonate.
Under normal circumstances soybean plants have the ability to actually change pH levels around their roots, but only to a certain degree.
“The plant will acidify the area around the root and then that iron that it comes in contact with becomes soluble and the plant can take it up,” she explained. “However, a soil that has a high presence of carbonates at the surface, will start to interfere with the plant’s ability to change the pH in the area around the roots, so the plant is going ahead and it is attempting to acidify the area around the roots and then these carbonates come in and they basically buffer against that change, keeping the pH higher, so the plant can’t actually get that iron.”
It’s not unusual to see the deficiency in the Red River Valley.
But carbonate isn’t the only cause of iron deficiency chlorosis; salinity can also trigger it, as can some plant injuries due to herbicide drift.
“The only way you’ll know if it’s one or the other is really by testing the soil,” Rieckman said.
Easy to diagnose
The good news is that iron deficiency chlorosis doesn’t usually last all season. As soil dries out, the plants are again able to take up iron.
Its yellow signature also makes it easy to spot and diagnose.
“The beautiful thing is that iron deficiency chlorosis shows up in the fields, it’s yellow and you can see it visually,” Rieckman said. “So take a picture and you can go back and see that problem come back year after year after year, because that problem is always inherently there, whether it’s a poor drainage problem with high pH and high carbonate presence or if it’s a salt problem.”
While there are rescue treatments available, they are too expensive to be viable for soybean growers. Primarily, they are used on strawberries, which can also experience iron deficiency chlorosis but have a different rate of return.
Rieckman said iron deficiency does cause yield loss, but exactly how much is hard to determine because it depends on how long iron deficiency chlorosis lasts and how severe it is.
“Observe, test, and if you know you have a risk, then you can select a variety that has the best tolerance,” she said. “That’s always the first step. It doesn’t mean you’ll have no symptoms that come up, but it means that you’ve got something that’s been shown to have tolerance.”
Other studies have shown planting rows farther apart, with higher plant populations can help offset the effects of high carbonate levels.
“We don’t know why that works exactly, but it might be that the plants work together as plant populations in rows increase — so, higher population works together to acidify the soil and remove more moisture,” she said.