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Articles by Birte Boelt
Total Records ( 4 ) for Birte Boelt
  Lars Monrad Hansen , Louise Lorentsen and Birte Boelt
  There is an increasing demand for organically grown pulses and cereal grains in Denmark, which is expected to cause a change in the typical organic farm structure away from dairy farming and towards arable farming. Spring field beans (Vicia faba) could be a popular break crop in organic agriculture. The black bean aphid (Aphis fabae) is generally considered to be a serious pest of spring-sown field beans in northern Europe, and field studies have shown that yield losses can exceed more than 50% due to attacks from the black bean aphid.
The use of insecticides in organically grown field bean crops is not permitted, but it has been known for a long time that the black bean aphid infests different varieties of beans to a very different extent. Therefore, partial resistance to the black bean aphid is one method of stabilizing yields. Another method of cultural pest control is intercropping and a third method could be a combination of both. Six field experiments involving the three methods were carried out. There was a significant difference between the number of aphids per plant on the three investigated bean varieties, where ‘Colombo’ was the most susceptible, ‘Quattro’ was intermediate, and ‘Caspar’ the most resistant variety. ‘Colombo’ intercropping with spring wheat and spring barley reduced the numbers of aphids per plant significantly, and also the number of plants infested. The harvesting of all crops took place during the last fourteen days of August.
It can be concluded that the growing of partial host plant resistant varieties of field beans or the intercropping of field beans with spring cereals separately will reduce the infestation with black bean aphids. If both methods are used, the reduction of infestation will be even higher and consequently also the yield.
  Lise C. Deleuran and Birte Boelt
  Establishment methods have proven to be of major importance for grass-seed production. The objective of this research was to test the effect of different sowing techniques on plant establishment and the subsequent seed yield. Perennial ryegrass (Lolium perenne L.) is used as the model grass due to its large importance in Danish agriculture.
In a three-year trial six different methods of under-sowing of perennial ryegrass in a spring barley cover crop were employed. Perennial ryegrass was either sown directly at different depths within the spring barley (Hordeum vulgare L.) rows or placed 2, 6, or 12 cm from the spring barley rows. Results of dry-matter yield indicate that the best establishment of the grass occurred when placing the grass 6 or 12 cm from the cover-crop row, and this is of importance in less vigorous grasses. Overall, no seed-yield difference has been observed for perennial ryegrass when placing the grass 2, 6, or 12 cm from the cover-crop row. Placement of the ryegrass seed crop 6 cm from the cereal row showed that a significant yield increase of 34-71 kg ha-1 can be obtained compared with sowing in the cereal row.
  Lise C. Deleuran , Rene Gislum and Birte Boelt
  To gain information about how widening of the row distance influences seed yields in first-year perennial ryegrass, experiments with four row distances in three types of perennial ryegrass were conducted at the University of Aarhus, Faculty of Agricultural Sciences. Perennial ryegrass was undersown at 12-, 24-, 36-, or 48-cm row distance in a cover crop of spring barley. The seeding rate in perennial ryegrass was 6 kg seeds ha-1 regardless of row distance. Although increasing the row distance from 12 to 48 cm had a negative effect on the yield component number of reproductive tillers, the yield was not affected in the first-year seed production in three perennial ryegrass cultivars. Regardless of row distance the seed rate was 6 kg ha-1 and hence in-row plant density in autumn and spring was higher at 48 compared with 12 cm; however, in all three cultivars the highest number of reproductive tillers was recorded at 12-cm row distance. Row distance affected seed yields of only the diploid amenity cultivar 'Allegro', where a row distance of 48 cm reduced the seed yield compared with 12- and 24-cm row distance. When data from the three cultivars were merged there was a positive correlation between the seed yield and seed weight (r=0.72***), whereas the correlation between seed yield and the number of reproductive tillers was negatively correlated (r= - 0.49***). This may reflect choice of cultivars in the experiment with the tetraploid forage cultivar 'Tivoli' having the lowest number of reproductive tillers, highest seed weight, and highest seed yield, and the diploid amenity cultivar 'Allegro' having the highest number of reproductive tillers, lowest seed weight, and the lowest seed yield. When the three cultivars were merged, there was a positive and highly significant correlation between seed weight and seed yield (r=0.72***). In contrast, there was no correlation between seed weight and seed yield when data were analysed for the individual cultivars. This suggests a cultivar-dependent relationship between seed weight and seed yield and furthermore between number of reproductive tillers and seed yield.
  Rene Gislum , Lise Christina Deleuran and Birte Boelt
  Repeated canopy reflectance measurements together with partial least-squares regression (PLSR) were used to predict seed yield in perennial ryegrass (Lolium perenne L.). The measurements were performed during the spring and summer growing seasons of 2001 to 2003 in three field experiments with first year seed crops using three sowing rates and three spring nitrogen (N) application rates. PLSR models were developed for each year and showed correlation coefficients of 0.71, 0.76, and 0.92, respectively. Regression coefficients showed in these experiments that the optimum time for canopy reflectance measurements was from approximately 600 cumulative growing degree-days (CGDD) to approximately 900 CGDD. This is the period just before and at heading of the seed crop. Furthermore, regression coefficients showed that information about N and water is important. The results support the development of an additional N- and water-application model which will calculate the application rate of N and water according to expected seed yield.
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