Digging holes with a Front End Loader

[rdbrumfield]

Have some more fun. Dig a deeper hole and bury them.

 

[cisco]

Not sure your intended dimensions are feasible, much less safe (cave-ins, remember?) with a FEL. Anyhow, 3 or 4 feet deep, with twice the distance on the trench length is reasonable. I've a 5' wide FEL on a Kubota 3410, and last weekend cut 9 small trenches for tree planting (latest "tree hugger" advice is to surround the planted tree - mine were mostly in 15 gallon pots from a nursery - with at least a few feet of soft earth on all sides but the bottom - I used a mix of mulch and earth I'd dug up). Anyhow, I had no major problems, in fairly firm ground, with scooping out 5' X 5' areas for the each tree (yeah, I didn't need that width, but with a 5' FEL - no choice) that were about 2 feet deep. With some modest slope to 2 sides of a trench, and 4WD, should be no big deal to dig a deeper hole - in 1 area I made a short trench (15' by about 3' deep) to plant some 2 trees, and drove my tractor down into the trench, no problem (if you have time on your hands), but had to scoop out enough earth to accomodate the width of my back tires.
Good luck. You'll do fine - but forget putting your tractor into a deep, narrow trench - at the end of the day, it's a beer that's appropriate, not another tractor to pull your tractor (or you) out of a collapsed trench.
Would a backhoe work better - you bet, but - if all you have is a FEL and time - - - -