Here the 1830 compositor set the singular desire rather than the plural desires, the reading in both manuscripts. He was probably influenced by the preceding singular this was. As discussed under Mosiah 18:10, 11, such usage is quite common in the original text and will therefore be restored here in Alma 47:4.
Summary: Restore in Alma 47:4 the plural desires, giving “this was the desires of Amalickiah”; such usage is found elsewhere in the original text.