No abstract

The production and persistence of legumes which may improve South Island high-country pasture in the Mackenzie Basin were studied. The initial soil test results confirmed toxic levels of aluminium (9 mg/kg, 0-150 mm soil depth) that has prevented the development of large areas of land traditionally grazed by merino sheep and beef cattle. A 3-year field experiment was direct-drilled in December 2012 with five rates (0, 0.5, 1, 2, and 4 t/ha) of surface applied lime and six legumes (lucerne, ‘Russell’ lupin, Caucasian clover, white clover, balansa, and Lotus pedunculatus) in three replicates. In Year 1, balansa clover and Russell lupin were the highest yielding legumes (7 t DM/ha), regardless of lime application rates. In Year 2 ‘Russell’ lupin was the highest (10.4 t DM/ha). Caucasian clover produced 4.6 t DM/ha and white clover and lucerne around 4.0 t DM/ha. Balansa clover (1.4 t DM/ha) and Lotus pedunculatus (2.5 t DM/ha) were the lowest yielding and they did not recover or persist after the initial grazing by merino sheep. These results confirmed that ‘Russell’ lupin and Caucasian clover thrived without the application of lime in this acidic soil with high Al levels.

This paper quantifies the effect of inoculation and lime on lucerne growth and nitrogen fixation over the establishment and following season. The field experiment at Ashley Dene, in Canterbury, had an initial soil pH of 5.2 and moderate exchangeable aluminium content (4.2 mg/kg). The 15N natural abundance (δ15N) method was used to quantify nitrogen fixation. The pH of the top-soil was increased to ca. 5.5 and the Al content was decreased to 2.0 and 1.3 mg/kg soil by the application of 1 and 2 t lime/ha, respectively. In Year 0 the dry matter yield increased from 3 to 4 t DM/ha with the addition of 2 t lime/ha. The nitrogen content of lucerne plants was 2.2% (w/w), and was unaffected by inoculant or lime in Year 0. Similarly, the δ15N was 0.81‰ and unaffected by inoculant or lime. In Year 1, the N percentage of inoculated lucerne plants was 4.2% (w/w) compared with 3.6% in uninoculated plants. The δ15N value was 0.81‰ in uninoculated plants compared with -0.23‰ in inoculated lucerne plants. The inoculated lucerne yielded 7.8 t DM/ha compared with 2.4 t DM/ha when uninoculated. The calculated proportion of legume N derived from atmospheric N2 (%Ndfa) estimated that 70% of the nitrogen content in the inoculated lucerne shoots was derived from nitrogen-fixation in Year 1. There was no effect of lime on lucerne DM, or δ15N values in Year 1. This suggests lucerne rhizobia tolerated moderate levels of Al in acidic soils. The application of lime and inoculant are therefore recommended for lucerne, particularly in areas where there is no history of lucerne. The available soil N was sufficient to meet crop demand in the establishing year. Lucerne was then reliant on biological nitrogen fixation for yield in Year 1 which suggests lucerne preferentially used soil available N in Year 0, before commencing N fixation. Keywords: Aluminium, lucerne, lime, Medicago sativa L., nitrogen fixation.