Alfalfa stands were negatively affected by this winter’s weather. Some farmers may be converting their alfalfa fields to soybean. Does the soybean seed need to be inoculated?

While there is very little information on this topic, we believe yes. You should inoculate soybean with Rhizobia when converting an alfalfa field to soybean. Here’s why:

Soybean planting date is absolutely critical to maximize yield (in most years and environments). Over the past few years, we’ve participated in a North Central Soybean Research Program (NCSRP) funded project with the goal of identifying causes of the “soybean yield gap.” (What factors are reducing soybean yield?) Across the Midwest, planting date was the most consistent management factor that influenced soybean yield.

Several calls last week with pictures of injured and/or diseased soybean seedlings.  For most of these situations we have the following scenario:  PPO herbicides (flumioxazin, sulfentrazone, saflufenacil) included as a component of the preplant burn down, fields planted 7 days later with fungicide treated seed, followed by 1 to 2 weeks of suboptimum growing conditions (between 40 to 50oF) for 2 weeks, and greater than 2” rain.  These conditions are very conducive to both Pythium damping-off and PPO injury.