The objective of this study was to determine if differences in nonsymbiotic N 2 fixation could account for the positive N budgets in the plant‐soil system of no‐till soils as compared with balanced or negative budgets under conventional tillage conditions (stubble mulch and plow) in a winter wheat ( Triticum aestivum L.) crop‐fallow rotation. This study was conducted on a Duroc silt loam (fine silty, mixed, mesic, Pachic Haplustolls) in western Nebraska from May 1982 to September 1983. Nonsymbiotic N 2 fixation was estimated using the C 2 H 2 reduction assay on intact soil cores from plow, stubble mulch, no‐till, and native sod management practices. Nitrogen fixation potentials of no‐till soils were twofold greater than those of plowed soils and were positively correlated with higher soil‐water contents for reduced tillage. The amount of N 2 fixed during one cycle of the wheat‐fallow rotation, however, as calculated from the C 2 H 2 reduction assay, was 0.33 kg N ha −1 yr −1 , which falls far short of the positive budget of 26 kg N ha −1 yr −1 found in the no‐till soil. Lower incubation temperatures, which simulated soil temperatures of tillage systems in the field, resulted in an even lower fixation than at 25°C.
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Lamb et al. (1987) studied this question.