The shelling of German trenches and the nomansland before the actual attack was immense. First of all the shelling would have been deafening, secondly, the nomansland would have been a moon-like scenery full of craters and barbwire, not a nice meadow.
When Eddie looks out the loophole, no mans land is a clear green field. When the Winter and Beckwith do the raid, Beckwith claims there is a a ton of wire left. During the final attack, there is no wire. Also, due to the weeks of bombing it is likely that the ground would be a bit rough and muddy.