"soy," 1670s; see soy. Soyaburger is attested from 1953.
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.”
Other food crops are wheat, barley, and the soya bean, but these not numerously so.Up To Date Business|Various
We cannot complete this part of the food industry without giving special consideration to the Tea and Soya industries.The International Development of China|Sun Yat-sen
The women, all the way to Soya Cape, the most northern point of Yezo, have given up tattooing a long moustache and their arms.