While we know that fallow tillage method affects water conservation and soil erosion control, effects on soil and fertilizer N dynamics are less well known. In this paper, we summarize results from our investigations of N transformation and cycling for two experiments established in 1969 and 1970 near Sidney, NE. In this research, the effects of three fallow tillage methods (moldboard plow, sub-till, and no-till) on changes in soil properties, N dynamics, and subsequent crop growth were studied. One experiment was on land, that had been broken from sod before 1920, seeded to crested wheatgrass [Agropyron cristatum (L.) Gaertn.] in 1957, and cultivated again since 1967 with the above three fallow tillage methods. Wheat (Triticum aestivum) was grown in a wheat-fallow sequence with and without 45 kg fertilizer N ha⁻¹. The second experiment was on land that was in native mixed prairie sod until 1969, and included a comparison of the three above tillage methods in a wheat-fallow system with plots remaining in native sod. During the first 13 years of study, total soil N loss from the surface 30 cm of soil (compared to the native sod) was only about 3% for the no-till system, compared to 8 and 19% for the sub-till and plow systems, respectively. For both experiments, considerable mineralization and nitrification of organic N occurred during the fallow period, with greatest rates for plowed fallow. No-till immobilized more labeled and total N in soil organic matter and in visible and partially decomposed crop residues on and near the soil surface. However, by harvest of the second crop grown after N-labeled fertilizer N was applied, little if any of the labeled N was found in visible and partially decomposed crop residues or as soil inorganic N, suggesting that most of the fertilizer N applied was immobilized in soil organic N or was lost. Deep sampling (to 15 m) of the Native Sod plots showed that several hundred kg of NO₃–N ha⁻¹ had leached beneath the crop root zone, presumably during wet years after fallow. For plowed plots, the quantity of NO₃–N beneath the root zone approximated the loss in total soil N from the root zone, suggesting there was a little net loss of soil N by denitrification or ammonia volatilization. For no-till, quantities of NO₃–N beneath the root zone exceeded the loss of total soil N during cultivation, suggesting significant N-fixation occurred by unknown mechanisms. These results show that fallow tillage system does affect soil and fertilizer N cycling and transformations and the availability of N to crops.