Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: "I have a surplus of kittens from that last batch we made, Reddit. AMA (ask me anything, あま)."
We caught more than enough fish ice fishing, so please take some if you'd like.
From the way they live, they seem to have quite an excess of money, don't you think?
There is an abundance of apples in our orchard.