Fruit & Vege Garden, page-1155

Indeed clay will not drain but clay soil are more fertile, due to higher cation-exchange capacity. If you have clay you need to gypsum to break it up.

So the key is to have a balance of sand clay and silt, after adding plenty of manure to my sandy soil I did get a good amount of silt but without clay to hold it after a year or so the sand to silt ratio went back to sand. Adding clay has improved my soil big time