Plant population, yield and water use of lucerne sown in autumn at four sowing rates

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Successful establishment of lucerne requires an adequate plant population to maximise yield and maintain stand persistence. The impact of autumn sowing lucerne at four sowing rates was investigated in a split-plot experiment at Lincoln University, Canterbury from 2007-2012. Emerged seedlings represented about 50% of the seeds sown regardless of the 7-16 kg/ha sowing rate. Self-thinning occurred at a faster rate from the higher sowing rates with populations of 80 plants/m2 in all treatments by Year 6. These populations ensured annual DM yields were maximised and similar across sowing dates and rates, in all years. However, the 10 t DM/ha yield in Year 1 was below the 13 t/ha average from Years 2-5. This suggests Year 1 crops were still in an establishment phase in their first spring after autumn sowing. This is supported by the initial spring water use efficiency (WUE) in Year 1 crops of 15-20 kg DM/ ha/mm of water used. This was lower than the 30-40 kg DM/ha/mm in subsequent years, and is consistent with Year 1 crops partitioning a higher proportion of assimilate below ground during the establishment phase. These calculated WUE values were probably overestimated because they were based on NIWA assumptions of 150 mm of available water for pastures, which appears to be too low for lucerne. Keywords: alfalfa, Medicago sativa