Nitrogen‐mineralization rates are needed to accurately determine N fertilization requirements to meet plant needs while minimizing environmental contamination. A spring wheat (Triticum aestivum L.)‐fallow (SW‐F) system was compared with a spring wheat‐winter wheat‐sunflower (Helianthus annuus L.) (SW‐WW‐SF) system on a Temvik‐Wilton silt loam (fine‐silty, mixed Typic and Pachic Haploborolls) at three N rates (0, 22, and 45 kg ha‐1 for SW‐F and 34, 67, and 101 kg ha‐1 for SW‐WW‐SF) under conventional, minimum, and no‐tillage. After 10 yr, soil samples were incubated to determine N‐mineralization rates. Cropping intensity, N rate, and tillage intensity interacted to affect N‐mineralization rates. Within the SW‐F system N‐mineralization rates in 0‐ to 0.05‐m depth were 8.2 ± 0.8 kg ha‐1 wk‐1 in the fallow phase vs. 5.0 ± 0.7 kg ha‐1 wk‐1 in the crop phase under conventional tillage and were 6.2 ± 0.3 kg ha‐1 wk‐1 under minimum and no‐tillage in both phases. The N‐mineralization rates were 2.3 ± 0.4 kg ha‐1 wk‐1 in 0.05‐ to 0.15‐m depth soils of the SW‐F system. In spring wheat, N‐mineralization rates in 0‐ to 0.05‐m depth soil were 9.9 ± 0.8 kg ha‐1 wk‐1 in the SW‐WW‐SF system vs. 5.6 ± 0.4 kg ha‐1 wk‐1 in the SW‐F system and in the 0.05‐ to 0.15‐m depth were 3.6 ± 0.1 kg ha‐1 wk‐1 in the SW‐WW‐SF system vs. 2.4 ± 0.2 kg ha‐1 wk‐1 in the SW‐F system Within the SW‐WW‐SF system, N‐mineralization rates in the 0‐ to 0.05‐m soil layer were 6.8 ± 0.5 kg ha‐1 wk‐1 under winter wheat vs. 9.9 ± 0.8 kg ha‐1 wk‐1 under spring wheat and 9.2 ± 0.6 kg ha‐1 wk‐1 under sunflower. In the 0.05‐ to 0.15‐m soil layer, N‐mineralization rates were 3.3 ± 1.0 kg ha‐1 wk‐1. More intensive cropping and conservation tillage increased N‐mineralization rates in this soil and may ameliorate the decline in N fertility associated with crop‐fallow systems.