Yield, oil constituents, and protein content of evening primrose (Oenothera biennis L.) seeds depending on harvest time, harvest method and nitrogen application

Evening primrose (Oenothera biennis) is cultivated as an oil seed crop because its seeds are rich in gamma-linolenic acid (GLA), which is used as both a nutritional and a medicinal supplement. O. biennis has good potential for agricultural production, but due to its indeterminate growth, it cannot be harvested at once as seeds are formed and ripened heterogeneously. Pot experiments were conducted to verify the influence of harvest time and harvest method on evening primrose seed oil quality and quantity under different doses of nitrogen. To understand more about the seed quality and quantity of autumn and spring-sown evening primrose one experiment was begun in autumn and the next in spring. From the results of three levels of nitrogen, most measured parameters especially seed yield and the content of oil, linoleic acid and gamma-linolenic acid were strongly influenced by nitrogen in both the spring and autumn experiments. A negative effect of nitrogen on the seed oil content was observed in this experiment. At the second harvest time oil content reached its maximum level in both experiments. In most cases, no differences were found among different harvest methods. Based on these results and considering all measured parameters, it can be concluded that the moderate level of nitrogen tended to produce high seed quantity as well as quality. The parameters such as plant variety, climate conditions, soil fertility, sowing time, etc. strongly influence the time of harvest. Although different harvest methods did not significantly influence most of the measured parameters, according to previous work and the present results, desiccation of the plants before harvesting is advisable due to the acceleration of seed ripening and the synchronization of seed maturity. (c) 2008 Elsevier B.V All rights reserved.