Just a quick note, I don’t know very much about daffodils, but I do know that soil conditioning is fraught with all kinds of situation-specific issues and gypsum is one of the additives that is not appropriate for ALL types of clay soils. Here is an example of a link that addresses this issue with greater expertise than I have:
http://www.ag.ndsu.edu/pubs/plantsci/soilfert/sf1321w.htm
Debbie in Western NC