"soy," 1670s; see soy. Soyaburger is attested from 1953.
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for soya
Though domesticated more than 3,000 years ago, “hardly any other food plant is as modern as the soya bean.”The Best of Brit Lit
March 4, 2009
Other food crops are wheat, barley, and the soya bean, but these not numerously so.Up To Date Business
But let us return to Soya Cape, where we have left the wreck.
It is from this point that one gets the first view of Soya Cape.
This Manchu-Mongolian plain is destined to be the source of the world's supply of soya bean.
It supplies the whole of Japan and a part of China with nitrogenous food in the form of soya bean.