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Nonsymbiotic Dinitrogen Fixation in No-till and Conventional Wheat-fallow Systems¹

ABSTRACT

The objective of this study was to determine if differences in nonsymbiotic N₂ 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 N₂ fixation was estimated using the C₂H₂ 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 N₂ fixed during one cycle of the wheat-fallow rotation, however, as calculated from the C₂H₂ 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.

¹ Contribution of the Dep. of Agronomy, Univ. of Nebraska-Lincoln. Published as Paper no. 8141, J. Series, Nebr. Agric. Exp. Stn., Lincoln, NE 68583. The research was conducted under Project no. 12-73.

² Former Graduate Assistant now Assistant Professor, Northwest Exp. Stn., Univ. of Minnesota, Crookston, MN 56716; Soil Scientist, USDA-ARS, Dep. of Agronomy, Univ. Nebraska-Lincoln; and Professor, Dep. of Agronomy, Colorado State Univ. Fort Collins, respectively.

Received for publication May 6, 1986.

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