Canola Grain Yield Response to Split Applied Nitrogen in Carrington, North Dakota.

This study was conducted in 2013 to evaluate response of canola (Brassica Napus L.) seed yield to split N fertilizer at the NDSU-Carrington Research Extension Center, ND. One-time application of N was made with uncoated urea either at planting at 0, 60, 105, 150 lbs N A^-1 (0, 67, 118, 168 kg N ha^-1), or as top-dress at 5-leaf growth stage at 90, 135, 150 Lbs A^-1 (101, 151 and 168 kg N ha^-1). Split treatments consisted of total N at 105, 150 180 lbs, applied at planting and as top-dress at the split rates of 60/45, 60/90, 105/45, 105/75 Lbs A^-1 (67/50, 67/101, 118/50, 118/84 kg ha^-1). Agrotain^TM-coated urea (ACU) was also applied as a single dose at planting at 150 Lbs A^-1, or at 5-leaf stage at 135 and 150 Lbs A^-1, and in split at 45/90 and 105/45 Lbs A^-1. The experiment was conducted as a randomized complete block design with four replicates. Leaf tissue N was assessed at 4-5 leaf stage just before fertilizer application. Results from pairwise comparisons (DMRT) showed yield differences were significant (p<0.05) between only the 105/45 lbs N split treatment (2454 Lbs A^-1 yield) and the check (1589 lbs ha^-1). Yields declined by 89 Lbs A^-1 from 90 to 135 Lbs A^-1 as single mid-season un-coated urea application. Additional decline of 8 kg ha^-1 was observed when urea N rates increased to 150 lbs N. Agrotain^TM-coated urea treatments on the other hand increased yields by 108 Lbs A^-1 with single mid-season N application of 135 lbs compared to the 150 lbs N. Mid-season drought from mid-June to August likely explains overall low significant responses. Oil was inversely related to N rates. Despite high numerical yield differences, gross margins did not justify the costs over single application rate applications.