In this 2014 trial at Kojonup-W
- Canola grain yield and gross margins were more dependent on nitrogen rates than the application timings.
- There was no effect of delayed nitrogen application on grain yield or gross margins up to 100kg N/ha.
- At 125kg N/ha, a significant yield and gross margins reduction was observed when nitrogen was applied as a three-way split (50kg within eight weeks, 50kg/ha at 12 weeks and 25kg/ha at 16 weeks after seeding) compared to when all of the nitrogen was applied within eight weeks of seeding.
|Property||Marbarrup, Kojonup - Ben Webb|
|Agzone 3 growing season rainfall (GSR)||400mm|
|Soil type||Loamy sand (4.14% organic carbon)|
|Paddock rotation||2013 - barley, 2012 - canola, 2011 - wheat|
|Sowing date||14 May|
|Seeding rate||Target density 40 plants/m2|
|Fertiliser (kg/ha)||100kg/ha of Superphos at seeding, 120kg/ha of Muriate of Potash and 400kg/ha of gypsum (17% Ca, 14% S) topdressed over whole site four weeks after seeding|
- Three cultivars: ATR Wahoo (Triazine Tolerant open-pollinated variety), Hyola 404RR (Roundup Ready hybrid variety) and Pioneer 45Y88CL (Clearfield hybrid variety) x 14 N treatments (kg N/ha) with timing spread between seeding, 8, 12 and 16 weeks after sowing (Table 1).
- Trial design: Split plot design with herbicide tolerant varieties as main plots and nitrogen rates and timings randomised within these, sown in three banks.
- Replications: Three
|No.||Total N||N splitting||N treatment name||Seeding||8WAS||12WAS||16WAS|
|2||50||Seeding and 8WAS||15N 35N||15||35||0||0|
|3||75||Seeding and 8WAS||15N 60N||15||60||0||0|
|4||100||Seeding and 8WAS||15N 85N||15||85||0||0|
|5||125||Seeding and 8WAS||15N||15||110||0||0|
|6||50||Two-way split||15N 10N 25N||15||10||25||0|
|7||75||Two-way split||15N 35N 25N||15||35||25||0|
|8||100||Two-way split||15N 35N 50N||15||35||50||0|
|9||100||Two-way split||15N 60N 25N||15||60||25||0|
|10||100||Three-way split||15N 60N 0N 25N||15||60||0||25|
|11||100||Three-way split||15N 35N 25N 25N||15||35||25||25|
|12||125||Two-way split||15N 85N 25N||15||85||25||0|
|13||125||Three-way split||15N 85N 0N 25N||15||85||0||25|
|14||125||Three-way split||15N 35N 50N 25N||15||35||50||25|
Assumptions used in gross margins
Oil bonus: +/- 1.5% per unit of oil (%) either side of 42%, with no oil ceiling.
Additional costs: Seeding, harvest, insecticides assumed to be $180/ha.
Nitrogen costs: $1/kg, application costs $8/ha per application.
RR grain: $508/t (decile 5 price).
TT costs: Seed $40/ha, herbicides $60/ha.
TT and CL grain: $523/t (decile 5 price).
Clearfield costs: Seed $60/ha, herbicides $97/ha.
The grain yield of canola increased significantly with increasing rates of applied nitrogen up to 100kg/ha and then flattened off (Figure 1). The grain yield of Hyola 404RR and ATR Wahoo were more than 150kg/ha higher than Pioneer 45Y88CL.
Delaying some of the nitrogen application after eight weeks or delaying from 12-16 weeks after seeding did not result in any yield reduction when the total rate of applied N was 100kg N/ha or less. However, a significant yield reduction of 230kg/ha was observed when 125kg N/ha was applied as a three-way split (50kg within eight weeks, 50kg/ha at 12 weeks and 25kg/ha at 16 weeks after seeding) compared to when all of the nitrogen was applied within eight weeks of seeding (Figure 2).
Grain oil concentration
Generally increasing rates of nitrogen resulted in a decrease in the oil concentration of canola, with the lowest concentration found at 125kg/ha (Figure 1). Delaying nitrogen application tended to reduce oil (Figure 3), except at 125kg/ha where the oil concentration improved with delayed application of nitrogen.
Varieties differed significantly in their oil concentration with Hyola 404RR containing 50.9%, ATR Wahoo 49.6% and Pioneer 45Y88CL 47.6% oil.
Canola gross margins began to plateau at 100kg N/ha (Figure 1). Thus application of 100kg/ha nitrogen produced higher gross margins than the nil, 50 and 75kg/ha treatments but statistically similar gross margins to 125kg/ha.
On occasions delaying nitrogen application reduced gross margins. For example, when 125kg N/ha was three-way split applied (50kg within eight weeks, 50kg/ha at 12 weeks and 25kg/ha at 16 weeks after seeding) a reduction of $138/ha was observed compared to when all of the nitrogen was applied within eight weeks of seeding (Figure 4).
On average, ATR Wahoo produced $135/ha and $38/ha higher gross margins than Pioneer 45Y88CL and Hyola 404RR, respectively.
At this site 100kg N/ha was the optimum rate for gross margins. There was significant yield and gross margin reductions when 125kg N/ha was three-way split applied (50kg within eight weeks, 50kg/ha at 12 weeks and 25kg/ha at 16 weeks after seeding) compared to when all of the nitrogen was applied within eight weeks of seeding. Up to 100kg/ha delayed application of some of the nitrogen from 8-12 or 16 weeks after seeding did not result in any significant grain yield or gross margin reductions.
This trial is one of a series conducted throughout Western Australia as part of the GRDC/DPIRD co-funded project Tactical Break Crop Agronomy in Western Australia. Thanks to Ben Webb for hosting the trial and to the Katanning RSU for trial management.