San Diego adds four from El Paso affiliate
The 28-year-old Decker has 154 career homers since being drafted in the 22nd round of the 2009 draft, most of any major-league-affiliated minor leaguer in that span.
Erlin has appeared in 24 career games with the Padres, most recently last September, going 7-8 with a 4.58 ERA.
Kelly appeared in six games in the majors before having Tommy John surgery in 2013. Jackson will be making his first appearance in the majors.