No abstract

Linseed (Linum usitatissimum L.) stems, which contain bast fibres, make up a considerable part of the linseed biomass, but are considered a by‐product of no value. The feasibility of cultivating existing linseed cultivars and breeding lines for dual‐purpose use of stem and seed was studied in 1995–97 in Jokioinen, Finland. Finnish linseed cv. Helmi was compared with 10 linseed genotypes and one flax cultivar for stem yield, ratio of stem yield to seed yield, and plant stand height and density. The stem yield of cv. Helmi averaged 1317 kg dry matter ha‐1. Significantly higher stem yields were produced by breeding lines Bor 15 and Bor 18 and cvs Gold Merchant, Norlin and Martta. The cv. Helmi produced lower stem yield than seed yield while breeding lines Bor 15 and Bor 18 and cvs Gold Merchant and Martta yielded more stem than seeds. The difference in the ratio of stem yield to seed yield between them and cv. Helmi was statistically significant. The mean plant stand height was 60.3 cm and the final plant density 594 plants m‐2. No relationship was found between stem yield and height or density. Within 2 days of seed threshing, stems of early maturing Finnish genotypes dried up in the field to nearly 15 % moisture content, even in the middle of September (1996). The early maturing breeding lines Bor 15 and Bor 18, with their significantly higher stem yields relative to cv. Helmi, are recommended for dual‐purpose use.

The aims of this study were to evaluate seed shedding in spring turnip rape (Brassica rapa L.) and spring rape (B. napus L.) and to assess the effect of delayed harvesting on seed yield loss. Experiments on spring turnip rape (cv. Emma) were conducted in 1988-1990 and on spring rape (cv. Topas) in 1989-1990 in Jokioinen (60o49'N, 23o28'E). Rimmed tin boxes were used to collect seed from shattered pods. They were placed between the continuous rows before pods started to shatter. The shed seeds were collected two to three times a week. Susceptibility and timing of pod shattering varies between spring turnip rape and rape. However, before optimal harvest date spring rape does not shatter significantly more than spring turnip rape. Spring rape starts to shatter more compared with spring turnip rape after its optimal harvest date. It is also more sensitive to weather conditions than spring turnip rape. Furthermore, pod shattering after optimal harvest time differs among years. Weather conditions are discussed as one possible cause of pod shattering

Plant development and stem yield of mono‐ and dioecious fibre hemp cultivars (Cannabis sativa L.), introduced to Finland from regions of lower latitude, were studied in field experiments under long‐day growth conditions in 1995–96. Plant density, plant mortality rate, stem elongation and stem yield were determined. Plant densities at seedling stage were less than the targeted viable seeds sown m−2. Seedling densities differed significantly among cultivars, but had no significant effect on plant mortality rate in 1996. Plant mortality during the 1996 growing season averaged 34 plants m−2. Stem elongation was measured at one‐week intervals throughout the growing time. The elongation among cultivars was different and depended on the date of measurement. Rapid elongation began five to six weeks after sowing and elongation was most pronounced in July. Dioecious cultivars were significantly taller than monoecious ones in 1995 but not in 1996 when hemp stands were dense, nitrogen was deficient and an infection of Botrytis vinerea was present. Dioecious cultivars produced higher stem yields than monoecious ones. However, in 1996 the difference in yield was not statistically significant among most of the cultivars, Cultivar Uso 11 was early maturing and produced highest stem yield among monoecious cultivars; it also competed well with the higher yielding dioecious cultivars.

The relation between stand density and structure of spring rape (Brassica napus L.) was described with the aid of comprehensive measurements of structure. The structural components measured were plant height, stem diameter at root collar, site of the lowest pod on the main raceme, number of pods on the main raceme, site of the lowest branch on the main stem, number of primary branches and number of pods on the branches. The experiment was conducted at two nitrogen levels, 110 and 180 kg ha', and was replicated in 3 years, 1988, 1989 and 1990. Stand density was varied by using five different seeding rates and the number of plants m‐2 evaluated immediately prior to harvest was used to express the stand density. In the years considered, the densities varied between 16 and 520 plants m‐2. The relationship between plant density and rape plant structure was adequately described each year by a mukivariate second degree polynomial model. Varying the nitrogen application rate seemed to have no influence on this relationship. Denser plant stands produced thinner and shorter plants, the shortening occurring in the pod‐producing section of the main raceme. Further, with increasing stand density, the number of branches decreased as did the number of pods on the branches and on the main raceme. These changes in plant structure retarded at densities over 150—200 plants m‐2. This seems to be the minimum density that should be achieved in rape stands.