NITROGEN PARTITIONING AND CYCLING IN BARLEY-SOIL SYSTEMS UNDER CONVENTIONAL AND ZERO-TILLAGE IN CENTRAL ALBERTA

Cropping systems which conserve soil, water and nutrients are needed o n the Canadian prairies. The objectives of this study were: (1) to ass ess the effects of urea injection on N partitioning in barley-soil sys tems under conventional (CT) and zero tillage (ZT); and (2) to measure the dynamics of fertilizer and soil N over the growing season. Twelve microplots were installed in each of CT and ZT plots located on a Bla ck Chernozemic soil and were fertilized (59 kg N ha-1) with N-15 urea solution, sown to barley (Hordeum vulgare (L.) 'Empress') and destruct ively sampled at the fifth leaf, ear emergence, grain filling and ripe ning growth stages. Distribution of N-14 and N-15 in shoots, roots, mi neral N, microbial N, and soil organic N were measured. The recovery o f fertilizer N in the soil-plant system was not different between trea tments. Microbial N and non-microbial organic N accounted for > 80 % o f residual N-15 in both treatments. Nitrogen budgets showed that grain removal from CT was 76 kg ha-1 and 56 kg ha-1 in ZT. Our study sugges ts that more N-15 from injected urea was converted to organic N under ZT than CT; thus ZT systems have the potential of conserving N. Tillag e practices affect the fate of added N.