Improvements in Soybean Iron Deficiency

2/18/2008 Kurt Lawton
There has been progress in the battle against Iron Deficiency Chlorosis (IDC) in soybeans, says George Rehm, University of Minnesota agronomist. A number of seed companies have improved varieties to the point where damage from this problem is less severe. In addition, field research in the past three growing seasons has shown that the problem is aggravated by high levels of nitrate-nitrogen in the soil and subsequently in the plant tissue. The high levels of nitrate-nitrogen apparently interfere with the metabolism of iron in the plant in the formation of the chlorophyll molecule.
Reduction in severity of IDC can be achieved by reducing the concentration of nitrate-nitrogen in the soil. This is easily accomplished by growing a competition crop with the soybean crop. Probably, the least expensive competition crop is oats.
Starting in 2006 and continuing in 2007, planting oats with soybeans and then killing the oats with Roundup has improved soybean yields in situations where IDC is a serious problem. In 2007, trials to evaluate this concept were conducted in Kandiyohi County. Without the planting of oats, the soybean yield waqs 3.6 bushels per acre. Using oats as a competition crop, the yield was 40.2 bushels per acre. That’s a substantial increase and the cost of planting oats in minimal.
There is a risk in this practice. The oats use soil moisture and, in a dry year, reduced soil moisture could have a negative impact on soybean yield. Therefore, time of Roundup application is important as shown by results from a time of Roundup application study. At another site, yield was 17 bushels per acre when there was no competition crop. When Roundup was applied when the oats reached a height of 6 inches, 12 inches, or heading, the respective yields were 14, 35, and 24 bushels per acre. The results from this site and others strongly suggest that the Roundup should be applied before the oats is taller than 12 inches.
All of this research was conducted under the leadership of Dr. John Lamb.
The seed companies will continue to improve varieties and there will be improvement in management of the competition crop. Although the problem has not been solved completely, there has been significant progress in the past three years. As a result, IDC is not now the problem that it once was.