Efficiency of fall-banded urea for spring wheat production in Manitoba: Influence of application date, landscape position and fertilizer additives

A 2-yr study was conducted to investigate the effects of application date, landscape position and a urease and nitrification inhibited formulation of urea on the efficiency of fall-banded N fertilizer under Manitoba conditions. To date, no studies have investigated how these factors interact to influence the efficiency of fall-banded N in western Canada. The effects of landscape position were apparent at three of the four sites, with significantly greater grain yields, straw yields and total recovery of N in the high landscape positions than in the low landscape positions. In the high landscape positions, there were no significant differences in crop response or recovered N among application dates in the fall and spring. However, in the low landscape positions, grain yields, grain yield increases and apparent recovered fertilizer N in the aboveground portion of the crop and in the soil (0–120 cm) were significantly greater for spring and late fall applications, when compared with early and mid-fall applications. At one site in the first year of the study, early fall-banded N with the urease and nitrification inhibitors produced greater increases in grain yield than early fall-banded N without the inhibitors in the low landscape positions. However, overall there was little agronomic benefit to the use of the additives, as there were few significant differences in crop yields or N uptake by the crop with the inhibitors than without, in either year or landscape position. The results demonstrate that selection of suitable timing for application of fertilizer N to optimize crop yields is much more critical for poorly drained areas within a field, or for poorly drained fields, than for better drained land. Key words: Fall-banded N, spring-banded N, landscape position, N-(n-butyl) thiophosphoric triamide (NBPT), Dicyandiamide (DCD), wheat (Triticum aestivum)