If you planted late soybeans, replanted or have just planted double-crop soybeans, don't be concerned if they appear a bit on the yellow tint side of green at the two trifoliate stage.
When soybeans have two sets of trifoliate leaves emerged, that is the V2 stage, explains Shaun Casteel, Purdue University Extension soybean specialist.
Examining plots of soybeans planted at different times at the Southeast Purdue Ag Center last week, he dug up some plants and demonstrated how to determine the growth stage of young soybeans. If the top edges of the leaves of the next trifoliate going to form on the plant are rolled up, like a burrito, you don't count it yet, Casteel says. If the leaves have separated and are apart, like a hard taco shell, you count it.
"The reason V2 soybeans still have a yellow cast or tint to the green color is because they are young and nodules with rhizobia bacteria that pull nitrogen out of the air aren't fully functional yet," he explains. "The nodules are forming but may not be active.
"The point to remember is that if soybeans at this stage have a yellowish cast, that's perfectly normal. There is nothing wrong, and there is nothing you need to do."
It's when that persists as the plant continues to grow and the plants don't green up that you begin to have concerns, Casteel notes. That has happened to some fields this year, he says. A combination of heavy crop residue last year, less breakdown of stalks overwinter than normal and wet soils and cool weather so far this year have some fields that have made it to V6 still not looking dark green or growing normally.
"That's not normal," he says. "If the situation is severe enough, apply 40 to 60 units of nitrogen as urea with a urease inhibitor on those fields right away. They should green up."