Epsilon Archive for Student Projects

Abstract

The inclusion of soybean in Swedish crop rotations would enable an increase in legume production in Sweden. Previous attempts to introduce soybean as a crop in Sweden have failed, but in recent years, new attempts have been made under experimental conditions. Soybean cultivars suitable for cultivation in Sweden belong to maturity group (MG) 000, as well as historically Swedish-bred soybean cultivars, such as Bråvalla. However, for these cultivars to fix N, compatible rhizobia such as Bradyrhizobium japonicum are needed. These are not native to Swedish soils and have to be introduced through inoculation. Inoculating seeds can have several beneficial effects on soybean traits, but this varies with the interaction between soybean cultivar, rhizobial strain- or species and environmental factors. Inoculants can have different formulations which have different properties and may affect rhizobial survival and inoculation effect. The aim of this thesis was to evaluate the effects the inoculation methods no-, liquid- or peat inoculation had on phenotypic traits and N-fixation in soybean cultivars suitable for cultivation in Swedish climate in both field- and greenhouse conditions. The peat- and liquid inoculants containing B. japonicum, as well as uninoculated control, were tested in a field trial on Gotland, Sweden, on the soybean cultivars Abaca, Gallec, Sussex, and Todeka (all MG 000), and in a greenhouse experiment in Uppsala, Sweden, on the cultivars Abaca, Gallec, Sussex and Bråvalla (historic). Inoculation of the seeds resulted in higher N content and %Ndfa in both the field trial (significant increase) and the greenhouse experiment compared to the uninoculated plants. The peat – and liquid formulations did not differ in performance in the greenhouse experiment, but the peat inoculant did overall perform better than the liquid inoculant in the field trial. This may be an effect of the protective properties of peat supporting rhizobial survival in field conditions. Inoculation of the seeds did not have a significant effect on the traits: plant height, height of the lowest node, leaf biomass, or N content in the leaves at flowering (field trial). However, inoculation significantly affected: TKW, yield, root biomass, stem biomass, root-/ stem biomass ratio, nodule weight, nodule number, and protein yield compared to uninoculated plants. The responses to the inoculants varied between the environments and between cultivars. In comparisons between the greenhouse experiment and the field trial, the traits affected by rhizobial survival (N content, nodule number and nodule weight) were enhanced in the greenhouse experiment, while traits probably limited by light intensity (TKW and yield) were superior in the field trial. The results showed that the interaction between cultivar x inoculation method had a significant effect on: root biomass, stem biomass, root-/stem biomass ratio, nodule number, nodule weight (GH), TKW, yield (GH), N content in biomass and seeds and %Ndfa in biomass and seeds. This thesis demonstrated that peat inoculation was superior over liquid inoculation in Swedish field conditions and that the MG 000 cultivar Sussex in comibination with LegumeFix had the greatest potential for generating high yield and protein yield out of the tested combinations, hence being suggested to Swedish farmers wanting to try soybean cultivation. However, further research is needed to confirm these results.