Growth, development and seed yield of autumn forage rape in response to sowing date and sowing rate

Minimal local data on the effects of sowing date and sowing rate on forage rape seed production in New Zealand has meant that current production practices are based on general overseas data for oilseed rape (OSR) rather than for forage rape seed. Oil seed rape is bred to produce high seed yields, whereas forage rape is bred to produce vegetative dry matter and therefore their seed production characteristics may differ. In a field experiment, we examined the effects of four sowing dates (February, March, April and May) and three sowing rates on the growth, development and seed yield of forage rape crops at Lincoln, Canterbury. Best seed yield was from March and April sowing. Delaying the sowing date beyond February increased seed yield from a mean of 2.3 t ha -1 to 3.3 t ha -1 for the March and April sowings and also increased the mean number of seed pods from 17 to 19. Delaying sowing to May caused poor emergence, because of wet and cold conditions. However, total dry matter (DM) yield decreased with delayed sowing. This was reduced from approximately 20 t DM ha -1 for the February and March sown crops to approximately 17 t DM ha -1 for the April sown crops. Sowing date had no effect on pod density or thousand seed weight (TSW). Sowing rate had no effect on all yield components except the number of pod per m 2 . This decreased from approximately 5000 for the 2 and 4 kg ha -1 sowing rate to 3700 for the 6 kg ha -1 sowing rate. Increased sowing rate resulted in reduced percentage establishment from 74% for the 2 kg ha -1 sowing rate to 51% and 65% for the 4 kg ha -1 and 6 kg ha -1 sowing rates, respectively. It is recommended that farmers sow forage rape seed crops in March to optimise seed yield. Soil conditions also encourage better emergence in March sowing. A sowing rate of 4 kg ha -1 was recommended as it ensured optimum establishment at reasonable seed costs.