VERNALIZATION AND SEEDING DATE EFFECTS ON YIELD AND YIELD COMPONENTS OF WHITE LUPIN

Understanding the agronomic importance of planting date and cold temperatures during germination may lead to the development of better management strategies for spring-sown white lupin (Lupinus albus L.). We conducted two experiments to determine optimum planting dates for spring-sown white lupin and to determine the effect of vernalization on plant morphology, yield, and yield components. In Experiment 1, field plots were planted in 15-cm rows at five planting dates (14-d intervals) at Staples, MN, from 1985 through 1989. In Experiment II, seeds were imbibed for 48 h and cold treated (vernalized at 1-degrees-C) for 14 d, and hand planted in 76-cm rows and compared with non-vernalized controls at 4 planting dates (main plots) at Staples and Becker, MN, in 1988 and 1989. Early to mid-April plantings generally produced the highest yields. Delayed planting past this yield maximum resulted in a 53 kg ha-1 d-1 decrease in yield, averaged over 11 location-years. Vernalization reduced node number 23 to 52% and plant height 8 to 53%. Height and node number were reduced by vernalization at every planting date, and varied widely across a range of temperatures to which the seedlings were exposed. This data provides evidence that vernalization is a continuous rather than discrete response. Yield was generally reduced by vernalization, except at later planting dates when 75% of the vernalized plot's yields were equal to or greater than controls (vernalization x planting date interactions were significant in all years). Yield differences were largely determined by the number of plants which produced fertile branch inflorescences. Pod number was increased at both the mainstem and the branch reproductive sites of these morphological types, compared with plants which set only mainstem pods. Seeds per pod and seed weight were also positively correlated with yield. Sowing white lupin within a relatively narrow window of seeding dates in mid-April is important to reduce the wide variation in performance often observed with this crop.