Planting Date and Cultivar Effect on Winter Rape Production1

Abstract

AbstractThe optimum planting date of six cultivars of winter rape (Brassica napusL.) was determined at Moscow, Idaho on a Palouse silt loam (fine‐silty, mixed, mesic pachic, Ultic Haploxeroll). The cultivars were seeded in early August, mid‐August, late August, and mid‐September of 1978, 1979, and 1980. Data were taken on winter survival, seed yield, oil content, nodes to fist flower, reproductive nodes, and plant height. Optimum planting dates for winter rape were early to mid‐August. Both winter survival and seed yield declined when the cultivars were established in mid‐September. A significant cultivar ✕ planting date interaction for both seed yield and winter survival occurred only in the 1978–1979 trial in which plants were exposed to a minimum temperature of −30°C. Seed yield at the late planting date of this trial was closely associated to winter survival (r = 0.93**; df = 14). Oil content, nodes to first flower, reproductive nodes and plant height were not highly sensitive to planting date. The utilization of cultivars with high levels of cold tolerance could probably improve performance of late seeded rape fields. Average seed yields of 3376, 3866, and 4682 kg ha−1were observed in the 1978 to 1979,1979 to 1980, and 1980 to 1981 trials, respectively. Average oil content of individual cultivars ranged from 406 to 490 g kg−1. Based on the results of this study it appears that cultivars of winter rape recently introduced from northern Europe have excellent potential as oilseed crops in the Pacific Northwest.