Nitrogen fertilizer and urease inhibitor effects on canola seed quality in a one-pass seeding and fertilizing system

▶ Urea or UAN increased protein, chlorophyll and glucosinolate in canola ▶ NBPT with the fertilizer increased oil and often reduced chlorophyll and glucosinolates ▶ Excess N and seedling damage can reduce canola seed quality. Field studies were conducted over three years on a clay loam (CL) and fine sandy loam (FSL) soil on the eastern Canadian prairies to evaluate the impact of urea and urea ammonium nitrate (UAN), with or without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), placed near the seed-row in a one-pass seeding and fertilizing operation on seed protein, oil, chlorophyll and glucosinolate content of canola ( Brassica napus L.). Application of N fertilizer as a side-band application at the time of seeding increased protein concentration and decreased oil concentration. Protein and oil yield increased with low to moderate N rates, but stabilized or fell with high N rates due to reductions in yield from seedling toxicity. Both chlorophyll and glucosinolate concentrations increased with increasing N rates. Use of UAN led to higher protein, chlorophyll and glucosinolate and lower oil concentration than urea on the CL soil. Use of the urease inhibitor NBPT generally increased oil concentration on both soils and reduced the chlorophyll and glucosinolate concentration on the CL soil. Observed difference may have been due to delayed maturity and reduced stand density caused by seedling damage and high N rates. High N rates applied as a side-band of urea or UAN near the canola seed row can negatively influence both seed yield and quality in canola and the negative effects may be reduced by the use of the urease inhibitor NBPT.