The objectives of this study were to evaluate if zero tillage had significantly altered the distribution of certain soil properties formally developed under the shallow cultivation (conventional tillage) soil management systems used on the Canadian prairies. To this end, concentration gradients of available plant nutrients, microbial biomass and mineralizable C and N, were determined in the Ap soil horizon from four locations representing zero and conventional (shallow) tillage systems of 2-, 4-, 12- and 16-yr duration. No significant change coud be detected in total soil organic C and N between tillages systems. Concentrations of plant-available P and K were slightly increased in the surface 0- to 2-cm depth after 16 yr of zero tillage. Except for the 2-yr tillage site, concentration gradients of potential microbial biomass C and N, and potential net mineralizable C and N were significantly greater in the surface soil under zero tillage in comparison to conventional tillage. The reverse situation was observed at the lower depth. The percentage of soil organic C and N that was in the microbial biomass also reflected the above trends. Accumulation of mineral N and calculated N mineralization potentials were closely correlated to both the initial microbial biomass N and the decrease in size of the latter during mineralization. The possible relationships of tillage induced change and redistribution in potential biological activity to N availability were discussed.

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.