Shaun Casteel has fielded calls from people who claim their soybeans are at the V6 stage, with six trifoliates exposed, and are stagnant. They don't seem to be growing.
"It's unusual but is a result of several factors related to coming out of winter and the spring we've had," he says. Normally by that stage soybeans should be actively producing nitrogen through rhizobia and growing. This year some of them are just sitting there."
In normal years, soybeans green up by V4 stage and pick up a dark green color, then start growing well. This isn't a normal year.
If you have a field that has reached the V6 stage and isn't growing, Casteel, the Purdue University Extension soybean specialist, is making a rate recommendation. He is actually recommending that people with these severe-case fields apply 40 to 60 units of nitrogen right away. He prefers applying urea.
If you do, be sure to include a urease inhibitor, such as Agrotain, or you may lose a good portion of what you apply into the atmosphere.
His preference would be a mixture of half regular urea with a urease inhibitor and half slow-release nitrogen. That would lessen the chances of shocking the rhizobia. Casteel says you're likely OK if you stay in his recommended range. If you apply too much N now, say 100 units per acre, you may shock them and they may not take off.
If you apply in the recommended range, the soybeans will utilize the N to take off and start growing. The rhizobia in nodules will use the sugars the plant produces to kick-start themselves. Even though rhizobia produce N which helps the plants, they do take a certain amount of energy away from the plant. In the early stages, in a year like this, that can be important.
If your plants are growing normally the extra N isn't needed and wouldn't help, Casteel concludes.