Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn

•SOC was lost over the study through the 0–120cm profile regardless of N fertilizer or tillage treatments.•Fertilization increased surface SOC stocks and reduced SOC loss in the 7.5–15 and 15–30cm depths.•Strip till completely reversed no-till surface SOC gain after the initial 5 years of NT.