The provincial ranger, Piyapong Leena, 27, was wounded by shrapnel in his stomach and leg.
The bomb was detonated as a five man patrol along railway passed near the provincial waterworks authority.
After the blast, an unknown number of men armed with AK 47 assault rifles attacked the soldiers and disengaged after a few minutes.
In an southern violence-related incident in Yala, five presumed insurgents were killed in Krongpinang district on Thursday when combined government security forces raided an area, believed to be a hideout of insurgents active there.
The two sides exchanged gunfire and five suspected insurgents were found dead.