Effects of sowing time and nitrogen fertiliser on canola and wheat, and nitrogen fertiliser on Indian mustard. I. Dry matter production, grain yield, and yield components

Abstract

Canola, Indian mustard, and wheat were grown under dryland conditions at Ariah Park and Cowra (canola only) in the cropping belt of New South Wales, Australia, to determine the effects of sowing time (canola and wheat) and nitrogen (N) fertiliser on the growth, grain yield, and yield components of the crops. Compared with an April sowing, the grain yield of canola at Ariah Park was reduced by 35% for a May sowing and by 67% for a July sowing. Canola yield at Cowra was reduced by 45% between early and late May sowings. Wheat yield declined by 35% between the May and July sowings at Ariah Park. Grain yields of canola and wheat at Ariah Park responded to N fertiliser in the April and May sowings, but not in the July sowing. Indian mustard had a higher yield than the comparable sowing of canola. Canola yields at Cowra were more responsive to N fertiliser than at Ariah Park, and increased from 0.5 to 2.9 t/ha with 100 kg N/ha. For each day that sowing canola was delayed at both sites after April-early May, anthesis was delayed on average by 0.52 days. For Dollarbird wheat, the delay in anthesis was 0.39 days per day sowing was delayed. Dry matter accumulation by the oilseeds was greatest during flowering, but before anthesis for wheat. Late sowing had little effect on the proportions of dry matter accumulated in a particular growth period. Irrespective of sowing time, grain yields and dry-matter harvest indices of the oilseeds were similar to values for wheat when differences in the biosynthetic costs of grain and straw production were taken into account. Late sowing usually resulted in a greater reduction in canola oil concentration than high N fertiliser rates. Canola oil concentration was reduced by 1.7 percentage points per 1°C increase in mean temperature during grain filling as a result of sowing late. It was concluded that N fertiliser could not compensate for the yield reduction in canola and wheat due to sowing late. Early sowing was essential to achieve high oil levels in canola.