Timing of nitrogen in low rainfall canola, Dalwallinu 2013 trial report

Page last updated: Wednesday, 13 June 2018 - 12:12pm

In general, as long as nitrogen is applied within eight weeks of sowing, there is no yield penalty.

How canola responds to nitrogen applied later than eight weeks has not been widely researched. Similarly how new generation canola such as RoundupReady (RR) hybrids respond to nitrogen has not been widely tested, particularly in low and medium rainfall areas. This trial is one of a series of 13 timing of nitrogen experiments DPIRD conducted in 2013.

Summary (key messages)

  • Canola grain yield increased with nitrogen application up to 50kg N/ha
  • Timing of nitrogen application had no effect on grain yield
  • Canola oil decreased as nitrogen rate increased
  • Applying nitrogen late (12 weeks after sowing) reduced oil%, but only if total N applied was 50kg/ha
  • Overall gross margins were similar at all rates of applied nitrogen or timing of nitrogen application - due to the decline of oil% as nitrogen increased
  • Hyola 404RR produced higher yields, oil and gross margins than CB Telfer TT - at all rates and timings of nitrogen application

Aim

To investigate the response to changing the nitrogen rate and changing the time of application. Canola yield and oil will be measured and RR hybrids will be compared with open-pollinated TT types (OP TT).

Trial details

  • Growing season rainfall (GSR April to October) = 204mm, GSR + stored water (estimate) = 277mm, Long term average GSR 222mm. Dry June and first half of July.
  • Soil type: Yellow deep sand (0.47% organic carbon), estimated to be 45kg N/ha available in paddock from soil and plant residues
  • Paddock rotation: 2012 - whea, 2011 - wheat, 2010 - lupin
  • 34 treatments: two cultivars (CB Telfer [TT open-pollinated variety] and Hyola 404 RR [RR hybrid variety]) x 14 N treatments (kg N/ha) with timing spread between seeding, and up to 12 weeks after sowing –see Table 1;
  • Three replicates
  • Sowing date: 9 May 2013
  • Seeding rate: Target density 30 plants/m2 - CB Telfer 2.7kg/ha, Hyola 404RR 3.4kg/ha
  • Basal fertiliser: 65kg/ha BigPhos treated with Impact at sowing, 25 June 120kg/ha Muriate of Potash.
Table 1 N treatment details
No. Total N Treatment Seeding  4WAS 8WAS 12WAS
1 0 0N 0 0 0 0
2 25 0N 25N 0 25 0 0
3 25 0N 0N 25N 0 0 25 0
4 25 0N 0N 0N 25N 0 0 0 25
5 25 25N 25 0 0 0
6 50 50N 50 0 0 0
7 50 0N 50N 0 50 0 0
50 0N 0N 50N 0 0 50 0
9 50 0N 0N 0N 50N 0 0 0

50

10 50 25N 25N 25 25 0 0
11 50 25N 0N 25N 25 0 25 0
12 50 25N 0N 0N 25N 25 0 0 25
13 75 25N 25N 25N 25 25 25 0
14 100 25N 50N 25N 25 50 25 0

Assumptions used in gross margins

  • Oil bonus +/- 1.5% per unit of oil (%) either side of 42%, with no oil ceiling.
  • Additional costs such as seeding, harvest, insecticides assumed to be $100/ha.
  • Nitrogen costs $1/kg, application costs $8/ha
  • RR costs – seed $31/kg, Herbicides $28/ha, Grain worth $482/t (CBH Pool Esperance 5/11/13).
  • TT costs – seed $2/kg, Herbicides $47/ha, Grain worth $502/t (CBH Pool Esperance 5/11/13).

Results

Both CB Telfer TT and Hyola 404RR responded to nitrogen in the same way in 2013. The yield of both varieties increased in response to nitrogen application up to 50kg N/ha. Hyola 404RR produced higher yields, oil (mean 50% versus 46%) and gross margins (mean $426/ha versus $238/ha) at all rates of nitrogen.

For any given rate of applied nitrogen, the timing of the nitrogen application had no effect on grain yield. Thus 50kg N/ha could be applied either at four weeks after sowing (WAS), eight weeks after sowing, 12 weeks after sowing or in split applications with similar grain yield responses.

Although nitrogen increased the yield of canola, it had a larger negative effect on oil%. Treatments without applied nitrogen averaged 50% oil and oil percentage decreased as nitrogen was applied. The oil% dropped approximately 0.04% for every unit of nitrogen applied up to 75kg N/ha. Not only did the rate of nitrogen reduce oil%, but the timing of nitrogen also had some effect on percentage oil. Applying nitrogen late at 12WAS reduced oil%, but only where the total rate of nitrogen applied over the season was high (50kg N/ha). If the total rate of nitrogen applied over the season was 25kg N/ha then applying nitrogen at 12 weeks had the same effect on oil% as applying nitrogen earlier in the year at seeding, four weeks after sowing or eight weeks after sowing.

There was no net economic gain in applying nitrogen in 2013, since the lost value from the reduced oil% and the cost of N exceeded the value of any increased yield. Similarly when the nitrogen was applied had no overall effect on gross margins.

Table showing as N rate increases oil concentration in the seed of canola decreased at a faster rate than yield increased
Figure 1          Effect of rate of nitrogen on grain yield (l.s.d = 76 kg/ha), oil (l.s.d. = 0.3%) and gross margins (l.s.d. = $21/ha) of canola in 2013 (mean of two varieties).

Conclusion

Previous field trials have shown canola to respond to nitrogen up to eight weeks after sowing. In this trial series in 2013 we have shown in a number of instances that canola responds to nitrogen up to 12 weeks after sowing. We will repeat these trials in 2014 to ensure we are not just seeing the response to a kind spring.

At West Dalwallinu/Miling in 2013 oil decreased at a faster rate than grain yield increased in response to nitrogen. Over recent years there has been a shift to markets with no oil limit. Therefore it will become increasingly important to have a good handle of soil nitrogen, target yield and the likely response of both oil and yield of canola if farmers are to maximise returns. We recommend people actively use tools like SYN to help with their nitrogen management.

Acknowledgements

This trial (13WH13) is one of a series conducted throughout WA as part of the GRDC/DPIRD co-funded project Tactical Break Crop Agronomy in Western Australia. Thanks to the Liebe group for hosting the trial and to the Wongan Hills RSU for trial management.

Contact information

Mark Seymour
+61 (0)8 9083 1143