Is it really necessary to sheet the clamp overnight?

You should always sheet down at night or if filling stops for any longer than 6 hours. It doesn’t take long and  will minimise air exposure and prevent rain ingress with uncovered silos. 

After sheeting, the oxygen level throughout the silo starts to fall quickly due to the continued activities of plant enzymes and aerobic microorganisms so it should all be gone in less than 30 minutes. If you do not sheet it will remain high in the outer layers. This will delay the onset of fermentation and allow aerobic activity to continue, especially near the surface, increasing losses - you may see a layer of poor quality silage when you open the clamp.  Prolonged aeration will lead to an increase in the numbers of yeasts, increasing the risk of aerobic spoilage at feedout losses.

Note: You can get an idea of how much  aerobic activity is occurring by pushing your hand into the forage the next morning – you will feel the heat.