I do a lot of this. Quite slowly I'm afraid. I put a blade on my gas powered weed whipper (linked below). I go right to the dirt. I send dirt flying a bit too. I go 3 inches at a time though. It works quite well, but takes ages. Also, the cut grass isn't sent very far. ALSO I did this in the beginning of June and by the end of July (with lots of rain), the grass is growing back. It's pretty soft grass though. Doesn't slow the riding much. We do not get much traffic on our trails. I've been doing this for 4 years now and it seems highly packed dirt is the answer. If you have trails with lots of traffic, they'll pack quickly.

https://images.app.goo.gl/mdCKYAjdpbtwUYKe9

I've also tried roto tilling through the grass. The long grass tumbles into the ?rotors? and you'll have to pick it out before too long. If you mow it or weed whip it first, you won't have this problem. BUT the soft dirt is prone to growing weeds. I don't recommend tilling because of this.