Accumulation, distribution and redistribution of dry matter and mineral nutrients in fruits of canola (oilseed rape), and the effects of nitrogen fertilizer and windrowing

Field studies were made at Ariah Park and Cowra to investigate the accumulation and distribution of dry matter and 12 mineral nutrients in fruits (pods) of canola (oilseed rape), and to assess the significance of redistribution of nutrients from the pod walls to the seeds. Flowers 4-6 from the base of the primary inflorescence were tagged at anthesis, and pods which developed from these were harvested at weekly intervals until maturity. Pods reached maturity 82 days after anthesis of the parent flowers. N fertilizer increased seed yields at both sites, but had negligible effects on the dry matter per pod, pod length, 1000 seed wt, seed number per pod, seed oil concentration, and concentrations of mineral nutrients in the pod walls and seeds. Similarly, there were no differences in these parameters due to locality, with the exceptions that seed oil per cent and concentrations of S and Mn in the pod walls and IVln in seeds were higher at Cowra than at Ariah Park. Pods had attained their maximum length and fresh and dry weights by the end of the first half of their development, but seeds had accumulated only 35% of their mature dry weight at this stage. Seeds gained dry matter after dehydration of the fruit began, but the pod walls did not. Seeds had 61% of the pod's dry matter, >70% of its P, N, Zn, Fe and Mg, 30-55% of its K, S, Mn, Cu and Ca, but <20% of its Na and C1. Dry matter was redistributed from the pod walls with 20% efficiency, and nutrients with from 17% (Cu) to 88% (P) efficiency; however, there was negligible redistribution of K, S, Ca, Na, C1, Fe and Mn from the pod walls. Redistributed dry matter and nutrients from the pod walls could have provided from 11% (dry matter) to 25% (N) of the amount in mature seeds. Concentrations of N, P, Mg, Mn, Zn and Cu in the pod walls declined as they developed, whereas those of Ca and Cl increased. Concentrations of nutrients in developing seeds remained fairly static. Windrowing plants when 40% of the seeds had changed to their mature colour did not affect seed oil per cent or concentrations of nutrients, but reduced seed size and seed yields by 10%. Data from the pod study also support the current recommendation to windrow when 40-60% of seeds reach their mature colour.