Nitrogen source and placement effects on stand density, pasmo severity, seed yield, and quality of no-till flax

Abstract

Field studies were conducted at two locations in western Manitoba over three years to evaluate the impact of rate, source, and placement of nitrogen (N) fertilizer on seedling emergence, disease severity, crop yield, and seed quality of flax (Linum usitatissimum L.). Urea, urea ammonium nitrate (UAN), and ammonium nitrate (AN) fertilizers were applied at 0, 30, 60, and 90 g N ha−1, pre-plant banded or side-banded 2.5 m to the side and 2.5 m below the seed-row, using a hoe-type opener with 20 m row spacing. Differences in stand emergence occurred from year to year, depending on the moisture conditions after seeding. Nitrogen fertilizer occasionally decreased stand density when side-banded, with effects being greatest with urea and UAN. The magnitude of stand decrease was generally low, although it may have restricted seed yield with high rates of urea fertilization in some years. Nitrogen applications frequently increased leaf and stem pasmo, but the effects of fertilizer source and placement were variable. Seed yield increased with N application except at a single site where soil N levels were high. Where differences existed among sources, yield was generally lower with urea than with the other sources, possibly related to seedling damage from the urea at higher rates of application, or to physiological effects of high ammonia:nitrate ratio nutrition during early growth. Seed quality for oil production tended to decline with increasing N applications due to lower oil concentration, lower iodine number, and a decrease in the concentration of high-quality linolenic and linoleic fatty acids. However, seed protein concentration increased with increasing N concentration. While risk of seedling damage and pasmo may increase with increasing levels of N fertilizer, either side-banded or pre-plant banded N applications still resulted in increased flaxseed yield. However, increasing N rate slightly decreased quality for oil production.