Recovery of 15N-labeled fertilizer by spring bread wheat at different N rates and application times

Abstract

Optimal N fertilization can improve the yield and quality of spring bread wheat in eastern Canada. This study aimed to determine the economical N rate for the production of spring bread wheat (Triticum aestivum L. 'AC Pollet') and to compare the effect of application times on the efficiency of fertilizer N use. The experiment was conducted during 2 yr on two sites of Sainte-Rosalie clay loam. The experimental treatments were arranged in a split-plot design with N rates (0, 30, 60, 90, 120, 180 kg ha−1) as the main plots and the application times of fertilizer N (15NH415NO3 applied at seeding and booting stages) as the subplots. Grain yield, grain protein concentration and straw N content of wheat were increased significantly with N application rates. The economic N rates were 90 and 120 kg ha−1 for 1993 and 1994, respectively. The recovery of 15N-labeled fertilizer (%FNR) in grain and straw was higher when applied at booting stage than at seeding in both years. In 1993, FNR varied from 37.8 to 45.7% for seeding and from 62.1 to 68.4% for booting stage treatments. The respective values were 23.1 to 30.4% and 41.3 to 50.7% in 1994. At each N rate, the proportion of N derived from fertilizer (Ndff) was higher in grain than that in straw when 15N fertilizer was applied at booting stage. The combined recovery of 15N fertilizer (% total FNR) applied at seeding and booting, as determined by the isotopic and the difference method, was in the same range, with a mean of 49.8% and 36.2% for 1993 and 1994, respectively. Soil N supplies for wheat during the growing season were 54 and 61 kg N ha−1 in 1993 and 1994, respectively. No priming effect of added fertilizer N on the mineralization of soil N was observed. Key words: Spring bread wheat, 15N-labeled fertilizer, split N application, fertilizer N recovery