Alpha acid factors

Anybody knows what influences the alpha acid of a certain hop plant? I have a Cascade hop that I planted, and it seems like it has a range of 5-7 AA. I heard the horse radish's strongness is affected by how dry the soil is. Does this apply to the hops, too?

Each variety has a range of AA% that is affected by many things. Soil, temp., nutrients, light, etc... IMO if the plant (hops) grows well and produces a good crop the AA% should be in the range of what the commercial product is. I don't think that even the commercial growers try to manipulate the AA, they just try to provide the plant with everything it needs and hope that mother nature is on board each growing year. Healthy plants with lots of sun make AA%.