Tactical use of nitrogen in canola to manage risk and include break crops in northern Wimmera

Time by rate of N for canola


27 Feb 2012

Project Description

Nitrogen fertiliser is often the single biggest variable cost to canola growers in the northern Wimmera.
Throughout the drought, canola was commonly dropped from the rotation in the region as it was seen as a risky crop. To counter some of this risk, some growers changed from pre-drilling all nitrogen fertiliser to splitting or deferring all nitrogen fertiliser applications.
Current recommendations suggest deferring N to the eight leaf stage is possible so long as reasonable amounts of N are present in the soil at sowing time, with rates far more important than timing. Defering allows growers to better assess seasonal conditions and therefore yield potential before committing to N application.
Research in CW NSW in wetter seasons the 1990s showed N could be applied at flowering and still provide yield response in a good season. The wet season of 2010 created many questions from growers about how late N fertiliser could be applied to canola.
In addition to timing, the ideal rate of N is queried as well as the efficiency with which N is used when applied early or later in crop growth.
Canola seed typically contains 40 kg N per tonne of grain, and a normal nitrogen use efficiency is around 50%. Therefore, current recommendations suggest canola requires 75 to 80 kg N from all sources to produce each tonne of grain. However, more recent trials by IREC/Better Oilseeds and demonstrations by Topcrop State Focus in 2001 suggest that a figure of 60kg N would probably suffice, particularly for higher yielding crops. The exception is in waterlogged situations.
The trial was undertaken in collaboration with a Wimmera farmers group and local agribusiness organisations, with support from the Grains Research and Development Corporation Its aim is to determine the optimal timing of N fertiliser and the rates for the northern Wimmera.