Dry matter accumulation and phenological development of four brassica cultivars sown in Canterbury

Four cultivars of brassica (cv Goliath rape, Gruner kale, Kestrel kale and Green Globe turnip) were sown in the field at four dates (16 January, 3 February, 18 February and 8 March) during one cropping season. Both sowing date and cultivar bad a significant effect on maximum dry matter yield. Yields of 11,000 to 4,500 kg DM/ha were recorded for the 16 January and 8 March sowing times respectively. Yields of 8,900, 7,800, 7,400 and 4,700 kg DM/ha were achieved by Gruner kale, Kestrel kale, Goliath rape and Green Globe turnip, respectively. All treatments reached leaf yields of around 4 t DM/ha, therefore the major contributing factor to total yield differences was stem production. Base temperature for leaf appearance was calculated using a least-variable and regression coefficient method (Yang et al., 1995). Data gathered from the months January to May gave an estimate of base temperature for leaf appearance of 4 degrees C. It is suggested that the reliability of this estimate could be improved by increasing the range of temperatures experienced by these crops. Leaf appearance rate (days/leaf) decreased during the season due to lower temperatures. When expressed against thermal time (base temperature 4 degrees C) the phyllochron for all four cultivars was found to be linear. Gruner kale, Kestrel kale, Goliath rape and Green Globe turnip had a phyllochron of 65, 68, 61 and 51 degrees Cd respectively. Leaf senescence rate (days/leat) followed the same trend as leaf appearance. However, lower temperatures and aphid damage during May caused accelerated senescence. When expressed against thermal time (base temperature 4 degrees C) leaf senescence was linear. The senescence rates for Gruner, Kestrel, Goliath and Green Globe were 93, 99, 76 and 70 degrees Cd, respectively. A thermal time model was developed to predict the effect of sowing time on brassica yield (assuming a base temperature of 4 T). The model showed that these brassicas accumulate dry matter at 1,100 kg DM/ha/ 100 degrees Cd. It also showed that stem yield accumulated at a linear rate (900 kg DM/ha/ 100 degrees Cd).