You need to make a measurement of an area so you take two clumps of dirt to seal in each side of your measuring tape, so it stays on the ground. This is the way people used to seal things back in the day, back when we didn't have fancy things like tape and glue.
You can also seal food (ふう) in dirt to make it last longer. That's how jerky came about, you know. Seal some meat underground and in a few months you'll have some tasty dried meats to chew.
By the way, this has another reading you should probably know. It’s ほう. Most sealing is done in the home (ほう), you know? So just think about eating food in your own home!
Currently there are no similar looking kanji which exist in the WaniKani learning system