Factors affecting growth and yield of winter oilseed rape (Brassica napus), 1985--89

Effects of agronomic factors on yield of winter oilseed rape were examined in multifactorial experiments, with a single-low (low erucic acid, high glucosinolate) cultivar (Bienvenu) in 1984/85 to 1987/88 and a double-low (low erucic acid, low glucosinolate) cultivar (Ariana) in 1986/87 to 1988/89. Establishment of September-sown plots was better than that of August-sown plots in 1984, 1987 and 1988, but not in 1985 when September was very dry. The total dry matter (DM) (kg/ha) of August-sown plots was much greater than that of September-sown plots throughout autumn and winter but by harvest the plant DM of late-sown plots was slightly greater. Combine-harvested yields of late-sown plots were greater than those of early-sown plots in 1984/85 (cv. Bienvenu) but not in 1988/89 (cv. Ariana); effects of sowing date on yields were smaller in other seasons, although late-sown plots generally had larger yields. Insecticide treatments increased combine-harvested yields in 1987/88 (cv. Bienvenu) and 1988/89 (cv. Ariana) and increased hand-harvested yields in 1984/85, by increasing the number of plants/M2. Fungicide spray treatments increased yields in all years except 1989, by increasing 1000-seed weights. Application of growth regulator sprays increased yields in 1986/87 to 1988/89; effects on cv. Ariana were associated with increased numbers of pods/plant. There were no consistent effects of spring nitrogen rates or timing on yield or yield components.