Miss Lauren Jones1, Dr Annamaria Mills1, Professor Derrick Moot1, Dr Xiumei Yang2
1Dryland Pastures Research Group, Faculty of Agriculture and Life Science, Lincoln University, Canterbury, New Zealand, 2The New Zealand Institute for Plant & Food Research Limited, Private Bag 4704, Christchurch, New Zealand,
Biography:
Lauren has an M.Sci. in plant science from her work on tall fescue seed production and is currently studying for her PhD on lucerne responses to phosphorous and water at Lincoln University.
Abstract:
The ability to predict the time of rapid stem extension in spring can be used to assist the development of lucerne grazing management plans. Therefore, the aim of this work was to validate the APSIM_Lucerne height function generated by (Yang et al., 2021) for early spring. Two experiments in 2022 and 2023 used four winter defoliation dates (01/06, 03/07, 17/07, 01/08) to measure the time and rate of initial stem extension (height) in spring. The data were used to validate the APSIM_Lucerne height function which is based on thermal time accumulation targets modified by photoperiod. The current exponential curve in ASPIM showed a poor agreement (R2 = 0.41) because it had limited data through the winter period. This was modified using the 2022 and 2023 field data, which showed the start of stem extension occurred at a photoperiod of 11.1 h. This was consistent with the original dataset. The change in photoperiod direction was accounted for calculating a weighted mean photoperiod from the start of the regrowth rotation (in a decreasing photoperiod) up to the 11.1 h increasing photoperiod until the end of rotation. This improved (R2 = 0.80) the prediction of plant height and is recommended for implementation into the APSIM_Lucerne framework. In the field, the start of maximum stem extension occurred at an 11.1 h in both years, which suggests this is the critical photoperiod required before rapid stem extension occurs. However, this remains to be validated in other environments.