The pilot reported that he was departing from a grass/turf runway, with a passenger and cargo onboard. As the airplane became airborne, it did not climb. After clearing trees at the end of the site, the airplane settled to the ground, and collided with terrain. The airplane sustained substantial damage to the wings and fuselage. In the pilot’s written statement to the NTSB, he stated he should have flown his cargo out first, and then returned for his passenger. The pilot reported no preaccident mechanical problems with the airplane.