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Nitrogen Transformations under Zero and Shallow Tillage¹

ABSTRACT

A field study was conducted with the objective of determining if differences occur in soil N transformations between zero and conventional tillage systems. Tillage comparisons of 2, 4, 12, and 16 yr duration were studied at four locations on Chernozemic soils in Western Canada. Determination of mineral N levels and immobilization of ¹⁵N-urea fertilizer indicated that only slight, periodic, transient differences occurred between tillage systems. The degree of N mineralization-immobilization turnover, which was associated with the incorporation of crop residues and level of labile organic matter in the surface soil, was not markedly affected by tillage differences. Over the growing season, fertilizer N entering the nonmicrobial biomass organic N pool increased relative to the microbial biomass pool, suggesting that in both systems N was entering more stabilized forms of organic N over time. These results would suggest that the differences in tillage system did not cause marked changes in the soil N cycle.

¹ Contribution from the Dep. of Soil Science, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0. S.I.P. no. R392.

² Research Scientist, Agriculture Canada, Charlottetown, Prince Edward Island; and Professor, Dep. of Soil Science, Univ. of Saskatchewan.

Received for publication January 26, 1984. Accepted for publication April 2, 1984.