Splitting of nitrogen in medium-high rainfall canola, Esperance 2015 trial report

Summary (key messages)

In this 2015 trial;

• Economic response plateaued at 75kg N/ha – lower than grain yield (125kg N/ha).
• Nitrogen applications at 12 and 14 weeks produced similar canola responses to N applied earlier in the year – but no added benefit.
• OP TT and hybrid RR varieties had a similar response to nitrogen timing and rate.

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

• Property: DAFWA site at Esperance Downs Research Station
• Agzone 6, growing season rainfall (GSR) (May to October): 320mm, GSR + stored water (estimate): 387 mm, dry October of 17mm compared to LTA of 43mm
• Soil type: gravelly sand (1.43% organic carbon)
• Paddock rotation: cereal 2014, canola 2013, sub-clover pasture 2011 and sub-clover pasture 2010
• 28 treatments: two cultivars (ATR Wahoo [TT open-pollinated variety] and Hyola 600 RR [RR hybrid variety]) x 14 N treatments (kg N/ha) with timing spread between seeding, and up to 14 weeks after sowing (see Table 1)
• Three replicates
• Sowing date: 28 April
• Seeding rate: Target density 30 plants/m² - ATR Wahoo 2.7kg/ha, Hyola 600RR 1.9kg/ha
• Fertiliser: 400kg/ha of gypsum (17% Ca, 14% S) top-dressed over whole paddock in late March. 100kg/ha of Superphos at seeding, 200kg/ha of Muriate of Potash top-dressed over whole site 4 June, 4kg MnSO₄/ha sprayed on 29 July, and 1kg ZnSO₄ sprayed on 4 August.

Treatment detail

Seeding N applied as Urea, top-ups applied as liquid N.

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 solid and $1.53/kg for foliar, application costs $8/ha.
• RR costs – seed $61/ha, herbicides $45/ha, grain worth $498/t (decile 5 pricing).
• TT costs – seed $5/ha, herbicides $60/ha, grain worth $518/t.

Results

Conclusion

At Gibson in 2015, we observed a positive grain yield and oil yield response up to 125kg N/ha. Once we took into account the cost of N we observed positive gross margin response up to 75kg N/ha, where the rate of return for investment in N would have been appoximately $3.

For 50N and 75N split application at seeding/eight weeks produced the same yield, oil, oil yield and gross margin as split at seeding/8WAS/12WAS. For 100N and 125N split applications had similar responses.

Considering a scenario where a grower may have put on 75N within first eight weeks – and would they have observed a response to an extra 25N at 12 or 14 weeks, we observed no extra yield if you apply 25N at 12 weeks, but extra yield if applied at 14 weeks, less oil percentage if you apply 25N at 14 weeks, but no difference yield if applied at 12 weeks and no response to N applied at 12 or 14 weeks for oil yield or gross margins. It appears our late application treatments are being imposed upon too high a background of applied N and we probably need to conduct our late N treatments at lower rates of N, that is apply 50N within 8 weeks and compare extra 25N at 8, 10 12, 14 to 20 weeks.

With the exception of higher oil from Hyola 600RR, we found very little difference between varieties and no variety x N treatment interactions.

Acknowledgements

This trial (15ED22) 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 the Esperance RSU for trial management. Pam Burgess (DAFWA, Esperance) provided technical assistance to ensure all treatments and measurements occurred in a timely and accurate fashion.