Effect of timing and nitrogen fertilizer application on winter oilseed rape (Brassica napus L.).: I.: Growth dynamics and seed yield

The field experiments conducted on the grey-brown podzolic soil in the four growing seasons (1998-2001) at Krzeslice Farm, central-western Poland comprised seven fertilization variants: 80(NF) + 80(CAN); 80(CAN) + 80(CAN); 80(AN) + 80(AN); 80(NF) + 50(CAN) + 30(CN); 80(CAN) + 50(CAN) +30(CN); 80(AN) + 50(AN) + 30(CN) (where NF - nitrofos NPK; CAN - calcium-ammonium nitrate; AN - ammonium nitrate; CN - calcium nitrate) and control (without N) applied in split rates at the beginning of spring regrowth (80 kg N ha(-1)), stem elongation (80 or 50) and flower buds visible stages (30). The yielding effect of tested fertilization variants was significant in comparison with the control (2.24 t ha(-1)). The highest mean seed yield (3.64 t ha(-1)) was collected from 80(AN) + 80(AN) and 80(CAN) + 80(CAN) variants. Mean values of 4 years indicate that the second N rate division (80 + 50 + 30) decreased yield, although not significantly in comparison with these two N treatments. Plants grown on these treatments have developed different patterns of growth to yield the seeds. These patterns were characterized by very high crop growth rate during flowering (above 21 g m(-2) day(-1)) and negative at maturation (down to -2.5 g m(-2) day(-1)). Plants fertilized with ammonium nitrate (80(AN) + 80(AN)) reached maximum growth rate earlier (65 days), which lasted longer (20 days) than plants fertilized with calcium-ammonium nitrate (71 days lasting 17.5 days). Plants grown on the control treatment reached the highest crop growth rate within 79 days (14.8 g m(-2) day(-1)), which lasted 15 days.