Though birdsfoot trefoil sets between 200 and 300 pounds of seed per acre in Iowa, harvested yields are commonly only 40 to 60 pounds. Use of chemical desicants followed by direct combining offers a possible solution.
Wiggans, S. C.; Metcalfe, D. S.; Thompson, H. E.; and Buchele, W. F.
"New Chemicals May Help Trefoil Seed Harvest,"
Iowa Farm Science: Vol. 10
, Article 3.
Available at: https://lib.dr.iastate.edu/farmscience/vol10/iss12/3