Seidenberger, 23, was a 12th-round pick in 2013 out of Texas Christian University. And because he was drafted in 2013, he didn't need to be added to the 40-man roster.
Seidenberger has a 4.37 ERA to show for his first 129 2/3 professional innings. He had a 4.07 ERA as a reliever last season in two stops -- Class A Advanced Brevard County and Double-A Biloxi.
He would likely pitch for Double-A San Antonio this season.
Seidenberger is the sixth left-handed pitcher Padres general manager A.J. Preller has acquired this winter. Logan Allen came from the Red Sox in the deal for Craig Kimbrel. Drew Pomeranz (A's), Jose Torres (A's), Buddy Baumann (big league free agent) and Ryan Buchter (Minor League free agent) are the others.
Pomeranz, Torres, Baumann and Buchter are on the team's 40-man roster.
Why the need for so many lefties? Consider this: The Padres allowed the most home runs to left-handed batters (98) and the most walks (304) in the big leagues a year ago.
Liriano, 24, didn't figure in the team's long-term plans as far back as last season when he wasn't added to the expanded roster in September.
Liriano is a career .277/.350/.435 hitter in parts of seven seasons with the Padres organization and reached the big leagues briefly in 2014. He had essentially been passed on the organizational depth chart by players like Hunter Renfroe, Travis Jankowski and Alex Dickerson.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.