The effects of two tillage practices [conventional till (CT) and no-till (NT)], five crop rotations [continuous spring wheat(CW), spring wheat-fallow (W-F), spring wheat-lentil (W-L), spring wheat-spring wheat-fallow (W-W-F), and spring wheat-pea-fallow (W-P-F)], and a Conservation Reserve Program (CRP) planting were examined on soil microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), and NH₄-N and NO₃-N contents in drylands of the Northern Great Plains. Each phase of the crop rotation (W-F, F-W, W-L, L-W, W-W-F, W-F-W, F-W-W, W-P-F, P-F-W, and F-W-P) was included in every year. The MBC, PCM, and NH₄-N contents were not influenced by treatments and averaged 1548, 210, and 5 kg ha^-1 at 0- to 20-cm, respectively. The MBN at 0- to 5-cm was greater in P-F-W (42 kg ha^-1) than in CRP, F-W, and W-W-F in CT, but was greater in F-W-W (35 kg ha^-1) than in W-F, F-W, L-W, and W-F-W in NT. At 5- to 20-cm, MBN was greater in W-F-W (137 kg ha^-1) than in other rotations, except in CW and P-F-W, in CT. Similarly, PNM at 0- to 5-cm was greater in W-P-F (13 kg ha^-1) than in other rotations, except in W-L, in CT. The NO₃-N content at 0- to 5-cm was greater in W-W-F (31 kg ha^-1) than in other rotations, except in W-F and W-P-F, in NT. At 5- to 20-cm, NO₃-N was greater in W-P-F (64 kg ha^-1) than in other rotations, except in W-L, in CT, but was greater in W-W-F (44 kg ha^-1) than in CRP, CW, and P-F-W in NT. Differences in soil and crop management practices and environmental conditions among rotations and phases of rotations altered N mineralization and availability in CT and NT in dryland soils, which could influence crop yields.