The glider pilot reported that, while en route on a local flight, the "lift died," and he decided to return to the departure airport. He was about 3 to 4 miles from the airport when the glider experienced a "moderate to severe sink," and he decided to set up to land in a nearby field. He added that, about 200 ft above the ground, the glider encountered a strong updraft that lasted between 15 and 30 seconds, and "even with full spoilers, it was obvious [he] would not be able to land." He stowed the spoilers, pitched up slightly, and focused on another landing site. The pilot further reported that, during touchdown at the alternate landing site, he noticed there were "sprinkler pipes and wheels." He added, "it looked like [he] would still hit the sprinkler pipes," so to avoid the industrial farm sprinklers ahead, the pilot abruptly pitched the nose down and landed hard on the field. The glider sustained substantial damage to the wings, fuselage, and empennage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the glider that would have precluded normal operation.