EVALUATION OF N FERTILIZER RATE AND TIMING AND WHEAT CULTIVARS ON SOIL RESIDUAL NITRATES

Nitrogen (N) fertilizer management for production of bread quality wheat may increase nitrate residues in the soil. To assess soil nitrate levels associated with bread quality wheat (Triticum aestivum L.) production in Eastern Canada, an experiment was conducted for 2 years at each of two sires in Quebec. Four cultivars (Columbus, Katepwa, Max and Hege 155-85), four N levels (0, 60, 120 and 180 kg N ha(-1)) and two N timings (all at seeding time or 60 % at seeding and 40 % at anthesis) were combined in a factorial arrangement on a Bearbrook clay and a Ste-Rosalie clay. Residual soil NO3-N levels were measured in the 0-20 and 20-60 cm soil layers. The cultivars used have potential as bread wheats. Cultivar effects on soil nitrate levels existed only in the Ste-Rosalie soil, suggesting that the cultivars used were better adapted to the conditions on the Bearbrook soil. Changes in soil NO3-N levels over winter indicated that mineralization had occurred. Calculated balance-sheet values were larger than measured residual NO3-N in the autumn of each year, indicating that NO3-N was lost from the systems, possibly due to denitrification. Potential increases in, and thus potential pollution from, residual soil NO3-N existed only at the 180 kg N ha(-1) level. Overwinter changes in soil NO3-N levels were proportional to the inverse of the fall NO3-N levels. Differences between sires were large for many of the variables measured.