title: Investigations into lotus species
Creators: name: Wedderburn, Mary Elizabeth
Publisher: name: University of Glasgow
Year: 1980
Subjects: subject: Lotus species.

description: The work described here was carried out as part of an extensive study by the Botany Department of the West of Scotland Agricultural College into the suitability of legumes, especially members of the genus Lotus, for the large scale improvement of low grade pasture. This study has involved lowland (44.7 metres a.s.l.) and hill land (206 metres a.s.l.) areas of south-west Scotland. Previous experimental work had shown that Lotus uliginosus Schkur cv. Maku (syn. L. pedunculatus Cav.), a cultivar of marsh birdsfoot trefoil bred in New Zealand, had promise for hill land areas and it was this cultivar which was used for all Lotus studies in this thesis. The main aims of this study were to investigate the conditions required for the improved establishment, growth and continued persistence of L. uliginosus cv. Maku under hill pasture conditions. To this end experiments were carried out in controlled environmental chambers, a glasshouse and in lowland and upland field conditions. Where possible, comparisons were made with Trifolium repens cvs. S184 or Huia. It was anticipated that the data accumulated could lead to the formulation of guidelines for the preparation and maintenance of land and other management practices, thus allowing good establishment, growth and persistence of this cultivar, or others, leading ultimately to improvement of the pasture and its grazing potential. The indirect method of measuring N2 fixation by acetylene reduction was used in modified forms for laboratory and field studies. The exact relationship between acetylene reduction (C2H2 → C2H4) and N2 (N2 → 2NH3) was determined for the cultivar Maku under laboratory conditions and found to be 2.98 moles of C2H2 reduced to every 1 mole of N2 fixed. The most reliable results when measuring acetylene reduction by cv. Maku in the field were obtained using a sample consisting of seven soil cores (5 cm diameter by 7.5 cm depth) with plant material, placed in a 4.6 litre glass incubation jar. Growth and fixation by Lotus cv. Maku and T. repens cv. S184 were studied in a glasshouse pot experiment using a Perlite medium, with pH levels 3.5 to 5.5, three phosphate levels (0, 15 and 30 kg P/ha) and presence and absence of trace elements. The addition of phosphate had no beneficial effect on Lotus when added at pH's 4.5 and 5.5. S184 had a greater response to 30 kg P/ha than Lotus. Increasing pH benefitted both species. The addition of trace elements two days after germination increased growth and effective nodulation of clover and effective nodulation of Lotus. The development of a Rhizobium - legume symbiotic association can be a key factor in establishment and growth and is affected by combined N. Three sources of combined N (NH4NO3, NaNO3 and KNO3) at various rates (0, 30, 70, 120 and 180 mg N/pot) were applied in solution to a Perlite medium into which cv. Maku and cv. S184 were transplanted. Supplies of NH4NO3 and KNO3 at 30, 70 and 120 mg N/pot increased shoot growth of Lotus without adversely affecting fixation but only addition of KNO3 increased total plant weight of both Lotus and clover. NaNO3 did not significantly affect growth or fixation by either Lotus or clover. To investigate the effect of combined nitrogen on nodule number, effective nodule weight and nitrogen fixation measurements, two levels of KNO3 (30 or 70 mg N/pot) were applied in solution to a Perlite medium in which cv. Maku and cv. S184 plants were growing. The nitrogen treatment was given at either 0, 6, 12, 18, 24 or 30 days after transplanting. Addition of nitrogen at time of or six days after transplanting improved the growth of both species without inhibiting fixation. The effect of a conunercial compound fertiliser containing slow-release N ("Enmag") added to cvs. Maku and S184 grown in a Perlite medium was studied under growth cabinet conditions. "Enmag" increased shoot growth and length of S184 when added at 30 and 70 mg N/pot but fixation was inhibited on addition of 120 mg N/pot. Addition of "Enmag" had no significant effect on Lotus plants. Studies were set up to simulate grazing by cutting and to measure the subsequent rate of recovery by cv. Maku to the level of N2 fixation prior to cutting, in a pot experiment under glasshouse conditions. A lag phase in acetylene reduction after cutting lasted eleven days. Cutting also resulted in a gradual loss of effective nodules and a decrease in root weight. (Abstract shortened by ProQuest.).