Albert Barnes Commentary 2 Chronicles 27:5

"He fought also with the king of the children of Ammon, and prevailed against them. And the children of Ammon gave him the same year a hundred talents of silver, and ten thousand measures of wheat, and ten thousand of barley. So much did the children of Ammon render unto him, in the second year also, and in the third." — 2 Chronicles 27:5 (ASV)

The Ammonites, who had submitted to Uzziah (2 Chronicles 26:8), revolted against Jotham. This revolt he firmly repressed; and, to punish it, he exacted a high rate of tribute for the three years following the termination of the war. The productivity of the Ammonite country in grain, which is indicated here, has been remarked upon as extraordinary by modern travelers.