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Are You Ready For This Soybean Problem?

Are You Ready For This Soybean Problem?
After a drought, high N carryover levels can reduce yields as much as 20 bushels per acre, unless you take steps to help the plants cope.

High levels of carryover nitrogen in drought areas can aggravate iron deficiency chlorosis in soybeans this year, says Ron Gelderman, South Dakota State University extension soil specialist.

Data from SDSU show soybean yield decreases of 20-22 bushels per acre with elevated carryover N levels compared to where carryover N is more typical.

Higher carryover N does two things to increase soybean IDC symptoms:

•The soybean has increased nitrate-N uptake which releases more bicarbonate ion at the root surface which can reduce iron availability and uptake by the plant.

You might see a lot more of these -- stunted soybean plants with iron deficiency chlorosis symptoms -- in fields with high levels of carryover nitrogen. Photo: Iowa State University

•The additional nitrate-N uptake by the plant increases the plant sap pH which decreases available plant iron that is transferred to plant cells.

Both processes can magnify IDC symptoms for soils prone to the condition, Gelderman says.

Symptoms can be particularly extreme when the early growing season is wetter than normal. In addition, plant stresses such as herbicide injury, salinity, disease, and nematodes can intensify IDC symptoms.

What to do?
Gelderman has this advice:

First, select an IDC tolerant variety for those fields or areas that are susceptible to IDC.

Other practices that can help include using a seed placement of an iron chelate product with most of its iron as the ortho-ortho form.

A higher seeding rate of up to 250,000 for 30-inch rows and 300,000 for narrower rows has lessened IDC symptoms.

A companion crop such as oats seeded at 1.5 bushels per acre with the soybean can help dry out the rooting area and utilize the carryover nitrate-N. Oats must be killed by the time it is 10-12 inches tall. Data from SDSU has shown an average of 6 bushel per acre increase to adding oats to these areas. Minnesota results have shown increases of 30 bushels per acre by use of an oat companion crop.

Minnesota studies also indicate that multiple management treatments such as variety, chelate, and companion crops can be combined for even greater yields than single treatments alone, Gelderman says.

Source: SDSU
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