That's not Glenn on the ground. Like the other poster said, it might be that other dude in Tyreese's group. However, that DOES appear to be the farm where they arranged to have that sit-down meeting last episode. Merle also looks like he may have taken a bullet to the heart/chest, based on the blood stain center mass. He isn't rotting much, although it does appear he may have been dead for a bit, considering how his face looks. His blade is also out, which suggests he was fighting or preparing for a fight when he died.
We can't see who discovered him, but the fact there appears to be collateral damage of other freshly killed people makes me think that something went down at the farm and whoever is in front of Merle discovered the aftermath. If we are to take how Merle looks as evidence of a time lapse, then whoever it was who found him didn't go with Merle to the meeting farm. However, if Daryl was with Merle, Daryl probably wouldn't hesitate to make sure Merle doesn't come back as a zombie. This makes me think that either Merle tried to go off on his own and enact his own plan to kill the Gov (and died) or Merle did something to ensure that Daryl got away before Merle dies