Mysterious Iron Deficiency Chlorosis in Soybeans—
The Product of Many Factors
The causes of iron deficiency chlorosis (IDC) in soybeans are not fully understood. Chlorosis is the product of complex interactions among many factors, including soil chemistry, environment and soybean physiology and genetics, says retired soil nutrient specialist George Rehm of the University of Minnesota. “This complexity explains why there is no easy answer to the problem.”
Iron is actually abundant in most soils, and plants need only a small amount. But soybeans are inefficient at absorbing and using iron. When the soil contains a lot of lime, or carbonates, the iron gets tied up in non-soluble forms and becomes even less available to soybeans. High concentrations of salts and excessive moisture exacerbate the difficulty. “In general,” says Jay Goos of North Dakota State University, “the wetter the soil, the worse IDC is; the more lime in the soil, the worse it is; the more salts, the worse it is.”
The weather plays a big role, too. In many areas, iron chlorosis is a problem only in wet years. In northwestern Minnesota and eastern North Dakota, however, IDC shows up most seasons, says Crookston grower Kevin Capistran. “As soon as the soil turns wet, you’ll see some symptoms of chlorosis.”
Other factors increase IDC severity, including cold soil temperatures, soybean seedling diseases and post-emergent herbicides. Chlorosis may also be associated with higher soil nitrate levels, Rehm says. That’s one theory behind the mysterious green wheel tracks.