Influence of source, timing and placement of nitrogen fertilization on seed yield and nitrogen accumulation in the seed of canola under reduced- and conventional-tillage management

Abstract

Field studies over 4 yr at two locations in southwestern Manitoba investigated the effect of N source, timing and method of placement on seed yield and N accumulation in the seed of canola (Brassica napus L. “Legend”) under reduced tillage (RT) or conventional-tillage (CT) management. The effect of N management on seed yield and N accumulation in the seed differed with soil type and tillage. Seed yields were frequently lower on the clay loam (CL) soil with fall-applied rather than spring-applied urea and urea ammonium nitrate (UAN), possibly due to losses through immobilization, denitrification and leaching. On the drier fine sandy loam soil (FSL), seed yield and N accumulation in the seed were generally similar with fall and spring N application, possibly because N supply was not as limiting as on the CL soil. Fall-applied anhydrous ammonia tended to produce higher canola seed yields than either fall-applied urea or UAN. Differences among fertilizer sources and between tillage systems were much less frequent with spring than fall N applications. However, under RT spring-banded anhydrous ammonia tended to produce higher canola seed yield than urea or UAN. Canola seed yield was lower with surface applications of N than with in-soil applications more frequently under RT than CT, presumably because surface residue under RT enhanced volatilization and immobilization losses. As differences in seed yield tended to be greater and more frequent under RT than CT, effective N management could provide a greater advantage under RT than CT. Key words: Conservation tillage, direct seeding, nitrogen fertilizer management, Brassica napus