Comparison of growth response and nitrogen uptake by canola and wheat following application of nitrogen fertilizer

Abstract

The seed yield response of canola (Brassica napus L.) and wheat (Triticum aestivum L.) to application of nitrogen (N), applied as urea (46% N), was measured in two field experiments in south Western Australia. Wheat produced significantly more seed than canola at all levels of applied N fertilizer, including the no‐N control. There was a small (<10%) wheat grain yield increase to applied N fertilizer at both sites. At each N fertilizer addition, the amount of seed produced per kg of N fertilizer applied for canola was about half that produced for wheat. Wheat reached the maximum grain yield at lower levels of applied N fertilizer than canola. Increasing the level of applied of N fertilizer significantly increased seed protein of both canola and wheat. There was no effect of N application on oil content of canola seed at Beverley, while the application of N at the Wongan Hills site resulted in a significant decrease in the oil concentration of canola seed. The relationships between the percentage protein in the canola seed and the percentage oil was given by Y (% oil concentration)=‐0.8474 ×+57.683, r2=0.74 (df=7), where x is the percentage protein and r2 is the coefficient of determination. Canola appears to be no more vigorous in vegetative growth than wheat as reflected in similar relative growth rates. Nitrogen uptake was higher for canola than wheat only at Wongan Hills and only then for the highest level of applied fertilizer N (138 kg ha‐1). Where no N fertilizer was applied at the Beverley site, the canola crop produced as much dry matter as wheat at early vegetative growth but absorbed less N than wheat at all stages of growth.