COMPARISON OF MODELS TO SIMULATE LEAF APPEARANCE IN WHEAT

Prediction on of leaf appearance in cereals is important for modelling canopy development and timing crop management practices. Four models which aim to predict leaf emergence on the basis of temperature and, i n three cases, photoperiod are compared against independent data from a wide range of sites, sowing dates and cultivars of spring and winter wheat. Three of the models behaved bery similarly and had root mean s quare errors of the order of one leaf in their prediction of leaf appe arance. The fourth model performed better in predicting differences in leaf appearance for different sowing dates than it did for latitudes. The prediction of the day of emergence of leaf number seven followed a similar response to that of leaf appearance. These results are discu ssed in terms of the hypothesised relationships between temperature, p hotoperiod and ontogeny within the models.