loam is soil with a fertile blend of organic and inorganic components of various sizes, which promote drainage and moisture retention. The source of the organics could be, composts or peat moss.
Loam: "Definition: [n] a rich soil consisting of a mixture of sand and clay and decaying organic materials"
Peat is "Keto tsuchi" but that is not the long moss.
Maybe you can find something here:
http://www.wafu.com/bd-192-32.htm
Another site has Sphagnum moss as "Mizu koke," which seems to be accurate as a back search on Mizu Koke comes up Bog moss.
Soil amendment really depends on what you're starting with. Some areas have very good soil, others are poor, still others are toxic, so I can't give you any guidance there. How about some neighborhood vegetable garden or garden center?
Good luck