pick up load limits?

The 2009 Explorer Sport Trac has a payload of 1407-1437 depending on features and options. In other words call it 1400 lbs.

That's the amount of weight you can add to the empty vehicle before you hit the gross weight rating.

So if you take 1400 and subtract YOUR weight and the weight of anyone else who will be riding with you and the weight of anything else you'll have in the vehicle, that's how much dirt you can haul without going over the truck's rated weight limits.

Dirt and soil generally weigh bout 2200 lbs per cubic yard, so you can probably haul about a half yard per trip. You might be over by a few pounds but if you're not going very far and not doing 70 mph on the highway you should be fine.

tHE INDIVIDUAL MAXIMUM AXLE LOAD WEIGHTS ARE LISTED ON THE DOOR POST STICKER. LOOK FOR THE REAR AXLE GROSS WEIGHT

It is not a trash hauler.  Get a truck.

1400 pounds regardless of trim level

Have you looked at your owner's manual?  Someone went through a lot of trouble to write that.