Results

Results

Observations 4 August – first topdressing
· Excellent establishment.
· Crop at eight leaf growth stage with buds visible under leaves and some plants beginning to elongate.
· Mouse damage in replicate 1 buffer and some signs of mouse grazing in the plot 16. Northeast part of replicate 1 less vigourous, possibly due to mouse grazing or denser volunteer barley population.
· Pre-drilling treatments clearly visible, with high N rates considerably more lush with darker green leaves than plots with no N pre-drilled.
· Weeds beginning to die. Volunteer barley yet to show signs of herbicide effects, and are fairly dense in northeast plots.
Observations - 1 September, four weeks after first topdressing
· Pre-drilled plots with high and moderate rates continue to look the best, although these rates which were also topdressed early appear to be catching up. The low rate appears nitrogen deficient, as do those plots without N applied.
· See http://anz.ipni.net/articles/ANZ0070-EN for images.

Effect of rate
· The addition of at the top rate enabled the presowing estimated yield to be achieved.
· Addition of nitrogen fertiliser compared with control plots increased yield by an average 35 per cent.
· Increasing rates improved yield, with highest yield of 2.12 t/ha achieved with the highest rate. The lowest rate was no different to the control.
· Oil content was inversely related to nitrogen rates. The effect of N rate on oil content was highly significant (p<0.001). However, more importantly, oil yield increased with nitrogen rate due to higher grain yields.

Table 1: Increasing nitrogen rate increased canola yield (t/ha) but reduced oil percentage (t/ha). Oil yield increased with nitrogen rates.

Rate	Mean yield	Oil % standardised to 8.5% moisture	Oil yield (t/ha)
High	2.12	41.89a	0.89
Moderate	1.85	42.82b	0.79
Low	1.50	43.68c	0.66
Control (no added N)	1.36	43.95c	0.60
LSD* (5%) when comparing high, low and medium rates	0.15	0.52
LSD when comparing rates with control	0.25	0.90

*NB: The LSD is the least significant difference. Here, when comparing two nitrogen rates, the difference between yields needs to be 0.15 t/ha or more to be significant. Otherwise, the differences may well be a chance finding.

Effect of timing
Timing alone did not affect yield or oil content (p>0.05).

Interaction timing x rate
Where yields exceeded 2.0 t/ha, they were not significantly different from each other.

For the high and moderate rates, yields were highest nitrogen topdressed at stem elongation or with a split application of nitrogen pre-drilled and topdressed at stem elongation. Pre-drilling all nitrogen produced highest yields for high nitrogen rates only.

Topdressing at early flowering alone was too late to maximise yields, although when rates were high, there was still a yield response - compared with the control.

Table 2: Nitrogen rate and rate x timing interaction affected canola yield.

Rate	Timing
	All predrilled	All topdressed stem elongation	All topdressed early flowering	50:50 split; predrilled & topdressed stem elongation	50:50 split; predrilled & topdressed early flowering	Control (no added N)	LSD (5%)
High	2.11	2.30	1.92	2.10	2.16	1.36	0.33
Moderate	1.80	2.11	1.63	2.03	1.69
Low	1.60	1.37	1.67	1.55	1.32

Low rates of nitrogen sometimes produced higher oil content, with some delayed applications increasing oil content further (Table 3). In contrast, this trend was not evident with the moderate and high rates, where delayed N often reduced oil content compared with pre-drilled N.

Table 3: Nitrogen rate and rate x timing interaction affected oil content (%).

Rate	Timing
	All predrilled	All topdressed stem elongation	All topdressed early flowering	50:50 split; predrilled & topdressed stem elongation	50:50 split; predrilled & topdressed early flowering	Control (no added N)	LSD (5%)
High	42.57	41.79	41.24	41.99	41.85	43.95	1.16
Moderate	44.05	42.52	42.10	43.06	42.36
Low	42.95	43.22	44.01	43.99	44.21

Oil content tended to follow yields inversely.

Figure 1: Yields and oil content were inversely related. Each dot represents the mean oil content and yield of each treatment, shown in Tables 2 and 3. Despite this, higher grain yields gave higher oil yields.