Organic matter is what I always see recommended (Leaves, grass clippings, manure, anything along those lines). I still think that if the ratio of sand to clay were high enough it would be a good thing, what is the composition of loam?
After all, what is the best type of soil that pops in your mind: Loam... a mixture of sand, silt, and clay!
Edited to add: This may not be a scientific article but it gives some explanations of the different types of soils.
http://homeguides.sfgate.com/d...
