Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year- round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn ( Zea mays L.)- soybean ( Glycine max L.)- winter wheat ( Triticum aestivum L.) rotation managed under Best Management ( BM) compared with conventional practices ( CONV). The study was conducted from May 2000 to October 2004 at Elora, Ontario, Canada. Cumulative NO3 leaching loss was reduced by 51% from 133 kg N ha(-1) in CONV to 68 kg N ha(-1) in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11 - 16% to leaching in CONV and < 4% in BM. High soil derived N leaching loss in CONV, which occurred mostly ( about 80%) during November to April was attributable to 45 - 69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency ( FNUE) was higher in BM ( 61% of applied) than in CONV ( 35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV ( for corn: 2000 and 2003, wheat: 2002, soybean: 2004) or higher in BM ( soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP ( no- tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.
