The 29-year-old scored two centuries during the tour of New Zealand earlier this year, but struggled for runs in the return meeting in May.
He returned to Somerset and showed some good form in the County Championship, but it has not been enough to convince the selectors, who have opted for Joe Root to open the batting alongside captain Alastair Cook in the four-day LV= Challenge match against Essex later this month.
Warwickshire's Boyd Rankin has also been included, despite the fact that he is yet to represent England in any format of the game.
"This match is a vital part of our preparations for the Investec Ashes after a period of limited overs cricket for a large number of the squad," said national selector Geoff Miller. "We have a very exciting two months of Test cricket coming up and it is important that we start well at Chelmsford next week. Kevin Pietersen has had no complications following his recent return to cricket after a knee injury which is pleasing and Graeme Swann is recovering well from a calf injury.
"We believe Joe Root is currently the best opening partner for Alastair Cook and he will open the batting against Essex. Joe has performed well for Yorkshire at the top of the order earlier this season and during his international career so far has proven to be very adaptable in all three formats and relished the challenge of international cricket."
England squad to face Essex on June 30
Alastair Cook, James Anderson, Jonny Bairstow, Ian Bell, Tim Bresnan, Stuart Broad, Steven Finn, Graham Onions, Kevin Pietersen, Matt Prior, Boyd Rankin, Joe Root, Graeme Swann, Jonathan Trott