Timing of nitrogen in low rainfall canola, Merredin 2014 trial report

Page last updated: Wednesday, 27 March 2019 - 10:46am

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 Roundup Ready (RR) hybrids respond to nitrogen has not been widely tested, particularly in low and medium rainfall areas.

Summary

With grain yield of less than 400kg/ha, there was no grain yield response to applied N and no economic response to applied N.
At ‘low rainfall’ N rates of 30kg/ha top-up N at 12 weeks gave a similar response to top-up N within eight weeks.

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

Table 1 Trial details
Property Merredin Research Station
Growing season rainfall (GSR, April to October) 193mm, GSR + stored water (estimate) = 255mm. Long term average (LTA, 1974on) 203mm and 240mm. Lower than LTA June and July, but above average September
Soil type Brown sandy loam (1.08% organic carbon), estimated to be 124kg N/ha available in paddock from soil and plant residues
Paddock rotation 2013 - wheat, 2012 - wheat, 2011 - wheat, 2010 - wheat
22 treatments Two cultivars (Sturt TT [TT open-pollinated variety] and Pioneer 43Y23 RR [RR hybrid variety]) x 11 N treatments (kg N/ha) with timing spread between seeding and up to 12 weeks after sowing (see Table 2)
Replicates Three
Sowing date 13 May
Seeding rate Target density 30 plants/m2 - Sturt TT 2.4kg/ha, Pioneer 43Y23 RR 1.5kg/ha,100kg/ha of Doublephos at seeding, 400kg/ha of gypsum (17% Ca, 14% S) top-dressed over whole site before sowing (kg/ha) and 120kg/ha of Muriate of Potash top-dressed over whole site 27 June
Basal fertiliser 100kg/ha of Doublephos at seeding, 400kg/ha of gypsum (17% Ca, 14% S) top-dressed over whole site before sowing (kg/ha) and 120kg/ha of Muriate of Potash top-dressed over whole site 27 June
Table 2 Treatment details
Treatment Name Seeding  8WAS 12WAS Total N 
1 Nil 0 0 0 0
2 10N seeding 10 0 0 10
3 30N in eight weeks 10 20 0 30
4 50N in eight weeks 10 40 0 50
5 70N in eight weeks 10 60  0 70
6 10N seeding and 20N 12WAS 10 0 20 30
7 10N seeding and 40N 12WAS 10 0 40 50
8 10N seeding and 60N 12WAS 10 0 60 70
9 30N in eight weeks and 10N 12WAS 10 20 10 40
10 30N in eight weeks and 20N 12WAS 10 20 20 50
11 30N in eight weeks amd 40N 12WAS 10 20 40 70

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 $126/ha.

Nitrogen costs: $1.33/kg or $1.5/L, application costs $8/ha

RR costs: seed $76/ha, herbicides $47/ha, grain worth $513t (five year decile price)

TT costs: seed $5/ha, herbicides $56/ha, grain worth $535/t

Results

Grain yield and gross margin results for this trial were extremely poor. Treatments had no significant effect on grain yield. Applying N reduced the concentration of oil of both varieties by an average of 0.08 units of oil per kg of applied N. The loss of oil with applied N combined with the cost of N resulted in a negative gross margin response to applied N.

At rates of N most commonly used in low rainfall areas of less than 30kg N/ha, it did not appear to matter when N was applied. Applying 30N within eight weeks or applying 10 at seeding and a top up at 12 weeks produced the same level of oil. At higher rates of total applied N it appeared timing of N had did alter the oil in the seed of canola. At a total rate of applied N of 50 or 70 applying 10 at seeding and then the top up at 12 weeks gave similar results to applying the top up N within eight weeks, however if the N was applied in more of a ‘split application’ with 30N within eight weeks and the top up at 12 weeks oil levels dropped. However applying 30N within eight weeks and then applying more at 12 weeks is highly unlikely to be undertaken by growers in low rainfall areas.

Sturt produced higher oil then Pioneer 43Y23 RR, but there were no differences between varieties for grain yield or gross margins. In addition there were no interactions between variety and N treatments.

Table 3 Grain yield (GY, kg/ha), oil concentration in seed (%) and gross margin (GM, $/ha) of two canola varieties in response to rates x timing of N at Merredin in 2014
- GY GY Oil Oil Oil GM GM GM
N Treatment Pioneer 43Y23 RR Sturt Pioneer 43Y23 RR Sturt Mean Pioneer 43Y23 RR Sturt Mean
Nil 193 208 42.9 43.9 43.4 -189 -154 -172
10N seeding  249 231 42.1 43.3 42.7 -180 -155 -168
30N in eight weeks  212 301 40.6 40.2 40.4 -225 -155 -190
50N in eight weeks 221 249 38.1 39.2 38.7 -254 -212 -233
70N in eight weeks  212 259 38.3 39.5 38.9 -287 -235 -261
30N in eight weeks and 10N 12WAS 197 245 38.7 39.7 39.2 -250 -198 -224
30N in eight weeks and 20N 12WAS 240 207 37.1 37.9 37.5 -247 -234 -240
30N in eight weeks and 40N 12WAS 245 197 36.0 37.7 36.8 -277 -268 -273
10N seeding and 20N 12WAS 250 188 40.7 40.1 40.4 -206 -212 -209
10N seeding and 40N 12WAS 206 250 38.1 39.8 38.9 -261 -210 -235
10N seeding and 60N 12WAS 202 216 37.8 38.9 38.3 -293 -257 -275
Mean 223 234 38.7 39.6 39.2 -248 -214 -231
- P - P - LSD P - LSD
Variety 0.765 - 0.034 - 1.2 0.19 - -
N Treatment 0.815 - <.001 - 0.7 <.001 - 75
Var.N treatment 0.243 - 0.688 - - 0.286 - -

Conclusion

With reasonably high background N levels in the paddock and low yield potential, the best option was to not apply N.

Acknowledgements

This trial (14MR18) 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 Merredin RSU for trial management. Laurie Maiolo provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.

Contact information

Mark Seymour
+61 (0)8 9083 1143
Sally Sprigg
+61 (0)8 9081 3153