Purcell, Larry C.; Salmeron, Montserrat; Ashlock, Lanny (2013). "Chapter 5". Arkansas Soybean Production Handbook - MP197. Little Rock, AR: University of Arkansas Cooperative Extension Service. p. 5. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2016.
Purcell, Larry C.; Salmeron, Montserrat; Ashlock, Lanny (2000). "Chapter 7". Arkansas Soybean Production Handbook - MP197. Little Rock, AR: University of Arkansas Cooperative Extension Service. pp. 2–3. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2016.
umn.edu
extension.umn.edu
Bennett, J. Michael; Rhetoric, Emeritus; Hicks, Dale R.; Naeve, Seth L.; Bennett, Nancy Bush (2014). The Minnesota Soybean Field Book(PDF). St Paul, MN: University of Minnesota Extension. p. 79. Archived from the original(PDF) on 2013-09-30. Retrieved 21 February 2016.
web.archive.org
Purcell, Larry C.; Salmeron, Montserrat; Ashlock, Lanny (2013). "Chapter 5". Arkansas Soybean Production Handbook - MP197. Little Rock, AR: University of Arkansas Cooperative Extension Service. p. 5. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2016.
Purcell, Larry C.; Salmeron, Montserrat; Ashlock, Lanny (2000). "Chapter 7". Arkansas Soybean Production Handbook - MP197. Little Rock, AR: University of Arkansas Cooperative Extension Service. pp. 2–3. Archived from the original(PDF) on 4 March 2016. Retrieved 21 February 2016.
Bennett, J. Michael; Rhetoric, Emeritus; Hicks, Dale R.; Naeve, Seth L.; Bennett, Nancy Bush (2014). The Minnesota Soybean Field Book(PDF). St Paul, MN: University of Minnesota Extension. p. 79. Archived from the original(PDF) on 2013-09-30. Retrieved 21 February 2016.