The pilot reported that he lost engine power while on base leg of the landing pattern and performed an off-airport landing on a farm field. The airplane sustained substantial damage when it touched down on the field's soft dirt. The pilot's accident report did not list any mechanical malfunctions with the airplane reference the accident flight. The pilot's safety recommendation stated, "Recommend that pilot check fuel tank selection and fuel content at start of each phase of flight." The airplane's kit manufacturer's "suggested pre-landing check list" included, "Fuel boost pump on. Check fuel quantity. Select proper tank. Verify that handle engages detent. ... NOTE We recommend completing the pre-landing check list before entering the pattern so that the pilots attention can be directed outside the airplane to clear for traffic while in the pattern."