Nitrogen-fixing bacteria in soybean nodules increase protein, oil and yield. But they don't work as hard where soil nitrogren (N) is high. So planting soybeans on meadow is not the most efficient use of N there.
Weber, C. R.
"Soybean Nodules Work for You,"
Iowa Farm Science: Vol. 20
, Article 2.
Available at: https://lib.dr.iastate.edu/farmscience/vol20/iss11/2