EFFECTS OF INCREMENTAL N FERTILIZATION ON GRAIN YIELD AND DRY MATTER ACCUMULATION OF SIX SPRING WHEAT (Triticum aestivum L.) CULTIVARS IN SOUTHERN MANITOBA

Abstract

A 3-yr study was conducted on three Orthic Black Chernozemic soils to determine the effects of incremental N fertilization on grain yield and dry matter accumulation and distribution of six spring wheat (Triticum aestivum L.) cultivars. Urea (46–0–0) was sidebanded at seeding in 40 kg N ha−1 increments from 0 to 240 kg ha−1 in the first year and from 0 to 200 kg ha−1 in the 2 subsequent years. Nitrogen fertilization increased the grain and straw yields of all cultivars in each experiment. The predominant factor affecting the N response and harvest index of each cultivar was available moisture. At two of the three sites, 91% of the interexperiment variability in mean maximum grain yield was explained by variation in root zone moisture at seeding. Mean maximum total dry matter varied by less than 12% among cultivars, but mean maximum grain yield varied by more than 30%. Three semidwarf cultivars, HY 320, Marshall and Solar, had consistently higher grain yield and grain yield response to N than Glenlea and Katepwa, two standard height cultivars, and Len, a semidwarf. The mean maximum grain yield of HY 320 was the highest of the cultivars on test and those of Katepwa and Len the lowest. Len produced the least straw and total dry matter. The level of N fertilization at maximum grain yield varied among cultivars, sites and years. Marshall and Solar required the highest and Len the lowest N rates to achieve maximum grain yield. The year-to-year variation in rates of N fertilization needed to produce maximum grain yield on a specific soil type revealed the limitations of N fertility recommendations based on "average" amounts and temporal distribution of available moisture.Key words: Wheat (spring), N response, standard height, semidwarf, grain yield