Articles
Photothermal models to predict onion (Allium cepa L.) bulbing
Article number
1118_10
Pages
65 – 72
Language
English
Abstract
Two photothermal models of onion bulbing with different assumptions about photoperiod are compared.
In Model 1, temperature drives bulbing and is modified by photoperiod with units given in thermal time.
In Model 2 photoperiod drives bulbing and is modified by temperature, with units given in accumulated hours or photo time.
Both models assume that a minimum temperature Tb and photoperiod Pb are needed before bulbing will occur.
Time to bulbing of individual plants was measured in an experiment with three sowing dates (late winter, spring and early summer) and four planting densities (15, 30, 60 and 90 plants m-2). The models were fitted to these results by minimising RMSD trying 42 different combinations of Tb and Pb. For Model 1 the RMSD was 0.038 and 0.002 for Model 2. Fitted values of Tb were 3 and 4°C for Models 1 and 2, respectively, and Pb was 9 hours for both models.
Model 1 predicted bulbing for winter and spring crops well but Model 2 predicted well for all sowing dates.
The models were validated with data from commercial crops from three different seasons.
Model 1 provided a good fit to the data with an RMSD of 7.0 days, but for Model 2 the RMSD was only 3.6 days.
These results strongly suggest that Model 2 better reflects the underlying physiology of bulbing.
In Model 1, temperature drives bulbing and is modified by photoperiod with units given in thermal time.
In Model 2 photoperiod drives bulbing and is modified by temperature, with units given in accumulated hours or photo time.
Both models assume that a minimum temperature Tb and photoperiod Pb are needed before bulbing will occur.
Time to bulbing of individual plants was measured in an experiment with three sowing dates (late winter, spring and early summer) and four planting densities (15, 30, 60 and 90 plants m-2). The models were fitted to these results by minimising RMSD trying 42 different combinations of Tb and Pb. For Model 1 the RMSD was 0.038 and 0.002 for Model 2. Fitted values of Tb were 3 and 4°C for Models 1 and 2, respectively, and Pb was 9 hours for both models.
Model 1 predicted bulbing for winter and spring crops well but Model 2 predicted well for all sowing dates.
The models were validated with data from commercial crops from three different seasons.
Model 1 provided a good fit to the data with an RMSD of 7.0 days, but for Model 2 the RMSD was only 3.6 days.
These results strongly suggest that Model 2 better reflects the underlying physiology of bulbing.
Authors
B.P. Searle, J.B. Reid
Keywords
temperature, photoperiod, thermal time, photo time, models
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