Yellow Soybeans and Nitrogen Fixation

Several questions have arisen over the last few days related to the "yellow" or "N deficient" appearance of many soybean fields across Wisconsin (Image 1). This symptomology is typical given the cool environmental conditions and slow growth that has plagued much of our soybean crop. In soybean, active N-fixtion does not begin until the V2-V3 (2 to 3 open trifoliates) growth stages. Even if you were to properly dig a soybean plant, identify and split a nodule, the red apperarance does not necessarily mean that fixation has fully begun (Image 2). Given our rainfall pattern over the last 24 hours and projected temperatures these yellow beans will likley recover in the next 3-5 days if not sooner.

Image 1. Yellow soybean crop.

Image 2. Soybean nodulation.