Jennifer Garner's real-life pregnancy was written into the series. Her need to be on maternity leave meant that the season was cut back to 17 episodes. It also necessitated the reduction of her action scenes, hence the drafting in of Rachel Nichols as her replacement. This coincidentally gave this season a cyclical feeling with the first one, in which Sydney Bristow was guided through the treacherous waters of espionage by her handler, Michael Vaughn. In this season, Bristow is performing the same role for Rachel Gibson.
The cornfield scenes were shot much later in the schedule. At that point, Jennifer Garner was four months pregnant and really starting to show.