02 Sep 2011

Wallup Ag Group Field Day

Photos and descriptions of treatments on September 01.

Wallup Ag Group Field Day

Images Taken September 01, 2011

Contributed by Rob Norton, IPNI

Click on the JPG file below to Enlarge


Low Rate 10 kg N
Moderate Rate 50 kg N
High Rate 100 kg N
All pre-drilled
Split half pre-drilled, half stem elongation
Split half pre-drilled, half early flowering
All Stem Elongation
All Early Flowering
The experiment is based on a water limited potential (top 60 cm water + rainfall) of a little over 2t/ha. To meet that yield potential, canola removes about 40 kg N per tonne of grain, and with an 50% nitrogen use efficiency, a 2 t/ha crop would need an N supply of 160 kg N.

The site had about 40 kg N at sowing.The soil organic matter content suggests that around 40 kg N would be mineralised during the season.

By the 4 to 6 leaf crop stage, the crop would have extracted between 50 and 70 kg N/ha (about 1 t/ha biomass with 6% N content).

At that stage the control would have been N stressed, and maybe the low N rate at sowing.

By stem elongation, crops would have around 2 t/ha, but the N content is lower around 5% - so they would have taken around 100 kg N/ha. None of the low N treatments would have been able to meet this N demand and so would be N stressed.

The application of early splits now helps the moderate rate catch up a little, while the N applied at the higher rate would have kept the crop growing without N stress.

By first flower, the better growing crop is around 4 t/ha of biomass with around 4% N, so that it has demanded 160 kg N by now. If there was no additional N supplied, this would meet a 2 t/ha yield potential. The pre-drilled moderate 50 N treatments and split 50:50 High N late split treatment probably have the growth to make the 2 t/ha.

The early split high N treatment has had by now 180 kg N supplied so – if water is not limiting – there may be another quarter tonne of grain from the extra 20 kg N.

It seems that the predrilled treatment is using the N more efficiently – a placement effect largely, but all the high N treatments – even the late top dressing – still look pretty good. The late topdress has recovered significantly – as it would have looked like the control prior to top-dressing.

Some Rules of Thumb – please treat these as guides only, the biggest variable is the efficiency of N use which is a culmination of many complex interactions between soil, plant and climate. The values below are largely taken from the PhD work of the author (Rob Norton) which was conducted in the Wimmera in the late 1980’s.

· Read your crop –even at early flowering if the lower leaves are yellow and dropping – N supply is likely to be limiting.

· Each 25 mm of rainfall has the potential to add an extra 250 kg canola per hectare. To achieve this extra yield an additional 10-20 kg N would be required.

· Each added tonne of grain yield will reduce seed oil content by around 2%

· Response

o With 50 kg N at seeding, and an extra 50 kg N will increase biomass at flowering by 50%.

o With 50 kg N at seeding, and an extra 100 kg N will increase biomass at flowering by 100%.

o With more than 120 kg N at seeding, then there will be little biomass at flowering response to extra N.

· Canola does manage to regulate its growth and yield so that harvest index does not fall under moderate to high N supply. Frost and high temperatures can cause harvest index to fall though.

· Although N is important other nutrients – especially S should be considered.

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