Influence of source, timing and placement of nitrogen on grain yield and nitrogen removal of durum wheat under reduced- and conventional-tillage management

Effective fertilizer management is critical to maintain economic production and protect long-term environmental quality. Field studies were conducted over 4 yr at two locations in southwestern Manitoba to determine the effect of source, timing and placement of N on grain yield and N recovery of durum wheat (Triticum durum L. 'Sceptre') under reduced-tillage (RT) and conventional-tillage (CT) management. The effect of N management on durum grain yield and N recovery differed with soil type and tillage system. On the clay loam (CL) soil, lower yields with fall- as compared with spring-banded N were more frequent under RT than CT. Lower yields occurred more frequently with fall-applied as compared with spring-applied urea ammonium nitrate (UAN) than when urea or NH3 was the N source. On the drier fine sandy loam (FSL) soil, fall applications of N generally produced similar to higher grain yield than did spring applications. Differences among fertilizer sources and tillage systems were much less frequent with spring than fall applications of N. Where differences occurred, durum grain yields were higher with in-soil than surface applications of urea or UAN. In-soil applications of urea and UAN increased durum grain yield as compared with surface applications more frequently under RT than CT on the CL soil where yield potential was high, whereas increases on the FSL were as common under CT as under RT. On soils with a high yield potential, enhanced immobilisation and/or volatilisation of surface-applied N may reduce grain yield by reducing available N, particularly under RT. Selection of a suitable source-timing and placement combination to optimise crop yield may be more important under RT than CT.