Effects of seeding rate and time of nitrogen fertilizer application on winter wheat in south coastal British Columbia

A two year field experiment was carried out in Delta Municipality approximately 30 km south of Vancouver, British Columbia on a Crescent silty clay loam. The study was designed to investigate the effects of seeding rate and time of N application on intensively managed winter wheat (Triticum aestivum L.) cv. Monopol. In 1988-89, seeding rates were: 200, 250 and 300 seeds m⁻², while in 1989-90 they were 150, 300 and 450 seeds m⁻². Nitrogen treatments consisted of 0 or 225 kg N ha⁻¹ as ammonium nitrate split-applied at Zadoks growth stages (GS) 22,31 or 37 (0/0/0; 0/125/100; 25/125/75; 50/125/50 kg N ha⁻¹). The number of established plants significantly increased with increasing seeding rate in both years. Shoot counts (main stem + tillers) were not significantly influenced by seeding rate in 1988-89, but a linear relationship existed in 1989-90. Shoot mortality, however, was higher at the high seeding rate and commenced earlier in the season. Time of N application had no effect on shoot production, nevertheless, N application enhanced shoot survival. Without N, disease incidence was higher at the lower seeding rate in 1988-89, while N application increased disease incidence over the control in 1989-90. Grain yield and yield components were not significantly influenced by seeding rate in 1988-89. In 1989-90, grain yield and grains m⁻² significantly decreased with increasing seeding rate, while number of heads m⁻² and number of grains head⁻¹ were not significantly affected. In both years, thousand grain weights were maximized at the lower seeding rate with added N. Grain yield and yield components, except for number of grains head⁻¹ in 1988-89, were significantly increased with N application over the control in both years, however, time of N application had no significant effect. Dry matter yields at GS 31 in 1988-89 and GS 37 in 1989-90 linearly increased with increasing seeding rate. At the lowest seeding rate, dry matter yield increased with N3 compared with N2 at GS 37 in 1989-90. Delayed N significantly reduced dry matter yields at GS 37 in both years and at GS 69 in 1989-90. With added N, dry matter yields significantly decreased with increasing seeding rate at GS 85 and at GS 92 in 1989-90. N uptake linearly increased with increasing seeding rate at GS 31 in 1988-89. Delayed N significantly reduced N uptake at GS 31 in 1988-89 and at GS 37 in both years. Harvest index was not significantly influenced by seeding rate in 1988-89, but it decreased significantly with increasing seeding rate in 1989-90. In both years, harvest index was increased with N application and in 1988-89 it was maximized with delayed N. While grain protein was increased with N application in both years, it was maximized in 1989-90 by delaying the first N application until GS 31. N application significantly increased soil mineral N at GS 37 in 1988-89 and throughout the growth period in 1989-90. Low levels of mineral N, as calculated by the difference method, remained in the top 0-50 cm of soil at the end of each season.Land and Food Systems, Faculty ofGraduat