This is Koshien’s dirt.
If you bury seven of these marbles, you will hear the voice of heaven.
Matt’s hobby is digging dirt.
The kanji and the word are exactly the same. That means they share meanings as well.
Since this word is made up of a single kanji, it uses the kun'yomi reading. Here's a mnemonic to help you to remember it:
You look through the soil. You're trying to find something. As you dig and sift, you come across not one but two cheeses (つち). Pull them out of the ground and put them in your mouth. How do the two cheeses taste and compare?